Networking A - Z

[Danno]

1 - 9

802 Standards

A family of standards developed by the US-based IEEE (Institute of Electrical and Electronic Engineers), an international organisation that develops standards for electronic and electrical technologies. The organisation uses a series of numbers, like the Dewey Decimal system in libraries, to differentiate between the various technology families. The 802 subgroup (of the IEEE) develops standards for local and wide area networks, otherwise known as LANs and WANs.

There are essentially three sections of interest for the wireless user:

802.11
covers standards for wireless local area networks (WLANs) e.g. office environments.
802.15
covers standards for wireless personal area networks (WPANs), typical range 10m.
802.16
covers standards for wireless metropolitan area networks (WMANs), otherwise known as Wi-Max, for typical ranges of up to 30 miles or 50km.


802.11 Standard

The following are the main 802.11 standards which specify an over-the-air interface between a wireless client and a base station or between two wireless clients:

* 802.11 - 1 or 2 Mbps transmission in the 2.4 GHz band. Now obsolete
* 802.11a - up to 54 Mbps in the 5GHz band
* 802.11b - up to 11 Mbps in the 2.4GHz band

802.11c - operation of bridge connections (moved to 802.1)

* 802.11d - worldwide compliance with regulations for use of wireless signal spectrum
* 802.11e - Quality of Service (QoS) support
* 802.11f - protocol for communication between access points to support roaming clients
* 802.11g - up to 54 Mbps in the 2.4GHz band
* 802.11h - enhanced version of 802.11a to support European regulatory requirements
* 802.11i - security improvements for the 802.11 family
* 802.11j - enhancements to 5 GHz signalling to support Japan regulatory requirements
* 802.11k - WLAN system management
* 802.11l - not used to avoid confusion with 802.11i
* 802.11m - maintenance of 802.11 family documentation
* 802.11n - 100+ Mbps standard for both 2.4 and 5GHz bands, expected 2005


10Base-T

An IEEE standard (802.3) for operating 10 Mbps Ethernet networks over Category 3, 4, or 5 twisted-pair cabling and a wiring hub, referred to as a 10Base-T hub.


100BASE-FX

The IEEE specification for 100 Mbps Fast Ethernet over fibre-optic cable.


100BASE-TX

The IEEE specification for 100 Mbps Fast Ethernet over Category 5 twisted-pair cable.


1000BASE-SX

The IEEE specification for 1000 Mbps Gigabit Ethernet over fibre-optic cable.


1000BASE-T

The IEEE specification for 1000 Mbps Gigabit Ethernet over Category 5 twisted-pair cable.


10 Gigabit Ethernet

A high-speed network standard that will use high-capacity cabling to provide data transfer rates up to 10,024 Mbps.

[Danno]

A

ABR (Area Border Router)

A router located on the border of one or more OSPF areas that connects those areas to the backbone network. ABRs are considered members of both the OSPF backbone and the attached areas. They therefore maintain routing tables describing both the backbone topology and the topology of the other areas.


ACK (Acknowledge)

When one computer sends a block of data to another over a network, the second computer sends an acknowledgment code back to indicate that the transfer was successful. If errors are detected in the transmission, the second computer sends a negative acknowledgment (NAK).


ACL (Access Control List)

A set of data that informs a computer's operating system which permissions, or access rights, that each user or group has to a specific system object, such as a directory or file. Each object has a unique security attribute that identifies which users have access to it, and the ACL is a list of each object and user access privileges such as read, write or execute.


ADSL (Asymmetric Digital Subscriber Line)

A form of DSL service that provides greater bandwidth (typically 1.5 to 9 Mbps) for downstream (from ISP to user) traffic at the expense of lesser upstream (from user to ISP) bandwidth (typically 16 to 640 Kbps). ADSL takes advantage of the typical pattern of network access on the Web by home users who frequently download large amounts of Web site data but upload relatively small amounts of data. In other respects, ADSL possesses all of the characteristics of DSL, including an "always on" combination of voice and data services, availability limited by physical distance, and high speed access compared to analogue modems.


AES (Advanced Encryption Standard)

A symmetric 128-bit block data encryption technique used in WLANs.


AP (Access Point)

A hardware device or a PC's software that acts as a communication hub for users of a wireless device to connect to a wired LAN.

There are various types of access points, also referred to as base stations, used in both wireless and wired networks. These include bridges, hubs, switches, routers and gateways. The differences between them are not always precise, because certain capabilities associated with one can also be added to another. For example, a router can do bridging, and a hub may also be a switch. But they are all involved in making sure data is transferred from one location to another.


A bridge connects devices that all use the same kind of protocol.
A router can connect networks that use differing protocols. It also reads the addresses included in the packets and routes them to the appropriate computer station, working with any other routers in the network to choose the best path to send the packets on.
A wireless hub or access point adds a few capabilities such as roaming and provides a network connection to a variety of clients, but it does not allocate bandwidth.
A switch is a hub that has extra intelligence. It can read the address of a packet and send it to the appropriate computer station.
A wireless gateway is an access point that provides additional capabilities such as NAT routing, DHCP, firewalls, security, etc.


API (Application Program Interface)

A set of routines, protocols, and tools for building software applications. A good API makes it easier to develop a program by providing all the building blocks.


ARP (Address Resolution Protocol)

An Internet Protocol that dynamically maps Internet addresses to corresponding physical (hardware) addresses on a LAN (Local Area Network). It is a low-level protocol (at layer 2 in the OSI model) usually implemented in the device drivers of network operating systems. ARP is most commonly seen on Ethernet networks, but ARP has also been implemented for ATM (See Below), Token Ring, and other physical networks. Ethernet network adapters are produced with a physical address embedded in the hardware called the MAC address.


ATM (Asynchronous Transfer Mode)

A high-speed networking standard designed to support both voice and data communications. It is normally utilised by Internet service providers on their private long-distance networks. ATM operates at the data link layer (Layer 2 in the OSI (Open Systems Interconnection) model) over either fibre or twisted-pair cable. ATM differs from more common data link technologies like Ethernet in several ways. For example, ATM utilises no routing. Hardware devices known as ATM switches establish point-to-point connections between endpoints and data flows directly from source to destination.


AUP (Appropriate or Authorised Use Policy)

Many public network services have an AUP. The AUP is a formal or informal document that defines the intended uses of the network, unacceptable uses, and the consequences for non-compliance. One often encounters an AUP when registering for a Web-based service or when working on a corporate intranet.

A good AUP will include provisions for network etiquette, limits on the use of network resources if any, and clear indications of the level of privacy a member on the network should expect. The best AUPs incorporate "what if" scenarios that illustrate the usefulness of the policy in real-world terms.


Access Control List (ACL)

See ACL


Access Point (AP)

See AP


Adapter (Also known as: NIC, LAN card)

A network adapter interfaces a computer to a network. The term adapter was popularised originally by Ethernet add-in cards for PCs but now network adapters refer in a broader sense to include PCMCIA (Laptop connector) devices and analogous wireless devices

Some network adapters are software packages that simulate the functions of a network card. These so-called virtual adapters are especially common in VPNs (Virtual Private Network).


Address Resolution Protocol (ARP)

See ARP


Ad-Hoc mode

A client setting that provides independent peer-to-peer connectivity in a wireless LAN. An alternative set-up is one where PCs communicate with each other through an AP. Also see Access point and Infrastructure mode.


Advanced Network Device Layer/Software

Term for the Device Driver level.


Advanced Encryption Standard (AES)

See AES


Aging

When an entry for a node is added to the lookup table of a switch, it is given a timestamp. Each time a packet is received from a node, the timestamp is updated. The switch has a user-configurable timer that erases the entry after a certain length of time with no activity from that node.


Antenna - Directional

The transmitted and received radio waves are concentrated in a particular direction so that the radio signal behind and to the sides of the antenna is reduced. The antenna direction is specified by the angle of the coverage pattern called the beam width.


Antenna-Omni-directional

Transmits and receives radio waves in all directions. The coverage area is approximately circular with the antenna at the centre.


Application Program Interface (API)

See API


Area Border Router (ABR)

See ABR


Association

The process of determining the viability of the wireless connection and establishing a wireless network's root and designated access points. A mobile unit associates with its wireless network as soon as it is powered on or moves into range.


Asymmetric Network

In a Symmetric computer network (e.g.SDSL), all devices can transmit and receive data at equal rates. Asymmetric networks (e.g. ADSL), on the other hand, support disproportionately more bandwidth in one direction than the other.

Besides DSL (Digital Subscriber Line) networking, the terms "symmetry" and "asymmetry" also apply to network design in more general ways. A symmetric network design affords all devices equal access to resources, whereas asymmetric networks segregate access to resources unequally. For example, "pure" P2P (Peer to Peer) networks that do not rely on centralised servers are symmetric, while other P2P networks are asymmetric.

In network security, both symmetric and asymmetric forms of encryption exist. Symmetric encryption systems share the same encryption keys between both ends of network communication. Asymmetric encryption systems use different encryption keys (such as public and private) on each communication endpoint.


Asymmetric Digital Subscriber Line (ADSL)

See ADSL


Asynchronous Transfer Mode (ATM)

See ATM


Authorised or Appropriate Use Policy (AUP)

See AUP


Autosensing (Also known as: Autonegotiation)

Network adapters that support both traditional and Fast Ethernet (10/100 adapters) choose the speed at which they run through a procedure called autosensing. Autosensing involves probing the capability of the network using low-level signalling techniques to select compatible Ethernet speeds. Autosensing was developed to make the migration from traditional Ethernet to Fast Ethernet products easier. Many hubs and switches are capable of autosensing on a port-by-port basis as some computers on a network may be communicating at 10 Mbps and others at 100 Mbps.


Auto Uplink

A feature that allows twisted-pair ports to sense if a normal (MDI-X) or uplink (MDI) connection is necessary and make the right link. It adjusts for straight-through or crossover cables in LANs.

[Danno]

B

BGP (Border Gateway Protocol)

A protocol for exchanging routing information between gateway host (each with its own router) in a network of autonomous systems. BGP is often the protocol used between gateway hosts on the Internet. The routing table contains a list of known routers, the addresses they can reach, and a cost metric associated with the path to each router so that the best available route is chosen. Hosts using BGP communicate using TCP and send updated router table information only when one host has detected a change. Only the affected part of the routing table is sent.


BPDU (Bridge Protocol Data Unit)

The IEEE 802.1D MAC Bridge Management protocol that is the standard implementation of STP. It uses the STP algorithm to ensure that physical loops in the network topology do not result in logical looping of network traffic. Using one bridge configured as root for reference, the BPDU switches one of two bridges forming a network loop into standby mode, so that only one side of a potential loop passes traffic. By examining frequent 802.1d configuration updates, a bridge in the standby mode can switch automatically into the forward mode if the other bridge forming the loop fails.


bps (bits per second)

A measure of data transmission speed over communication lines based on the number of bits that can be sent or received per second. It is often confused with bytes per second (Bps). While "bits" is a measure of transmission speed, "bytes" is a measure of storage capability. 8 bits make a byte, so if a wireless network is operating at a bandwidth of 11 megabits per second (11 Mbps or 11 Mbits/sec), it is sending data at 1.375 megabytes per second (1.375 Mbps).


Bps (Bytes per second)

Note the uppercase 'B' as opposed to bps. Also written as bytes/sec and bytes/s. Also see bps.


BSS (Basic Service Set)

When one AP is connected to wired network and a set of wireless stations it is referred to as a BSS. An Extended Service Set (ESS) is a set of two or more BSSs that form a single subnetwork.


Backbone

The part of the communications network intended to and designed to carry the bulk of traffic, it provides connectivity between subnetworks in an enterprise-wide network.


Backbone Router

Routers designed to be used to construct backbone networks using leased lines.


Backup

The process of copying computer or other networking device files to a second medium, normally disk or tape, as a precaution in case the primary medium fails. Ideally the backup medium should be kept in a different location from that of the primary.


Bandwidth

The amount of transmission capacity that is available on a network at any point in time. Available bandwidth depends on several variables such as the rate of data transmission speed between networked devices, network overhead, number of users, and the type of device used to connect PCs to a network. It is similar to a pipeline in that capacity is determined by size: the more bandwidth a network provides, the more data can flow through it. In wireless networks, standard 802.11b provides a bandwidth of 11 Mbps whereas 802.11a and 802.11g provide a bandwidth of 54 Mbps.


Basic Service Set (BSS)

See BSS


Beacon

A system packet broadcast by the AP to keep the network synchronised. A beacon includes the ESSID, the AP address, the Broadcast destination addresses, a time stamp, a DTIM (Delivery Traffic Indicator Maps) and the TIM (Traffic Indicator Message).


Beta Firmware

Firmware which has undergone first, or alpha, testing and has then been released, usually to a selected user group, for the second, or beta, series of tests. The purpose of the beta test is to carry out testing in the real world with users who will use it in a different way to those in the development team.


Bit

The smallest unit of data transfer on a computer network. Bits represent the two binary values "on" or "off." Bits are often stored on computers as the digital numbers '1' and '0', but in networking, bits can also be "encoded" by electrical signals and pulses of light. In computer networking, some network protocols send and receive data in the form of bit sequences which are called bit-oriented protocols, an example being PPP.


BitTorrent

A leading P2P network system for the download of movies, software, music and other large files over the Internet.


Bits per second (bps)

See bps


Bluetooth Wireless Technology

A technology specification for linking portable computers, PDAs and mobile phones for short-range wireless transmission of voice and data featuring a dynamic topology called a Piconet or PAN. Bluetooth is a frequency-hopping technology in the 2.4 GHz frequency spectrum, with a range of 30 feet (9m) and up to 11Mbps raw data throughput, but more generally 1Mbps. Compared to Wi-Fi, Bluetooth networking is much slower, a bit more limited in range, and supports many fewer devices.


Bootstrap Protocol (BootP)

An Internet protocol that enables a diskless workstation to discover its own IP address, the IP address of a BootP server on the network and a file to be loaded into memory to boot the machine. This enables the workstation to boot without requiring a hard or floppy disk drive.


Border Gateway Protocol (BGP)

See BGP


Bridge

A network device that connects one LAN to another LAN that uses the same protocol (for example, wireless, Ethernet or token ring). Wireless bridges are commonly used to link buildings in campuses. Bridges operate at the data link layer (Layer 2) of the OSI model. Bridges inspect incoming traffic and decide whether to forward or discard it. Bridges serve a similar function as switches, that also operate at Layer 2. Traditional bridges support one network boundary, whereas switches usually offer four or more hardware ports. Switches are sometimes called "multi-port bridges" for this reason.


Bridge Protocol Data Unit (BPDU)

See BPDU


Bridging versus Routing

Bridging is the process of passing packets to another network segment without regard to the network operating system. Bridged packets are passed to the data link layer of the OSI model, as opposed to routed packets, which are delivered to the network layer. In an environment where diverse network operating systems exist, a bridge can move data between the networks, but cannot deliver packets all the way up through the network. However routing can deliver packets to discreet addresses in the network.


Broadband

Any type of transmission technique that carries several data channels over a common wire. DSL service, for example, combines separate voice and data channels over a single telephone line. In DSL, voice fills the low end of the frequency spectrum and data fills the high end.

In home networking, "broadband" usually refers to high-speed Internet access using this transmission technique. Both DSL and cable modem are common broadband Internet technologies. So-called broadband routers and broadband modems are network devices that support both DSL and cable.


Broadband Router

A router which combines the features of a traditional network switch, a firewall, and a DHCP server. Broadband routers are designed for convenience in setting up home networks, particularly for homes with high-speed cable modem or DSL Internet service. Broadband routers support file sharing, Internet connection sharing, and home LAN gaming.


Broadcast

A packet sent to all devices on a network.



Broadcast storm

Multiple simultaneous broadcasts that typically absorb all the available network bandwidth and can cause a network to fail. Broadcast storms can be due to faulty network devices or network loops.


Buffer

A temporary memory that holds data until a device is ready to accept it.


Byte

A byte is a sequence of bits and in all modern network protocols, a byte contains eight bits. In computer networking, some network protocols send and receive data in the form of byte sequences. These are called byte-oriented protocols e.g. TCP/IP and the order in which bytes are sequenced is called the network byte order. The maximum size of a single unit of transmission for these protocols, the MTU, is also measured in bytes.


Bytes per second (Bps)

See Bps

[Danno]

C

CA (Certificate Authority)

An organisation that provides certificates and provides a mechanism for verifying their authenticity. It is a method whereby the computer would have a pre-assigned certificate, such as Verisign or Thawte, that is necessary for the IPSec-based authentication algorithm to use for generating keys to exchange between the two VPN devices. It is generally recognised as a more secure method of authentication.


CAM (Continuously Aware Mode)

Mode in which the adapter is instructed to continually check for network activity.


CAT5 (Category 5)

CAT5 is an Ethernet cable standard defined by the Electronic Industries Association and Telecommunications Industry Association of the USA (commonly known as EIA/TIA). CAT5 is the fifth generation of twisted pair Ethernet cabling supporting Fast (100 Mbps) Ethernet and comparable alternatives such as ATM. As with all other types of twisted pair EIA/TIA cabling, CAT5 cable runs are limited to a maximum recommended run rate of 100m (328 feet).

Although CAT5 cable usually contains four pairs of copper wire, Fast Ethernet communications only utilises two pairs. CAT5 enhanced cable (CAT5e), supports short-run Gigabit Ethernet (1000 Mbps) networking by utilising all four wire pairs and is backward-compatible with ordinary CAT5.


CAT6

CAT6 cable is similar to CAT5, supporting not only Gigabit (1000 Mbps) Ethernet but also communications at more than twice the speed of CAT5e. However it is more expensive.


CDMA (Code Division Multiple Access) and TDMA (Time Division Multiple Access)

The standards for wireless communications on WANs in North America.


CIDR (Classless Inter-Domain Routing, Classless Internet Domain Routing)

This is an efficient method for specifying IP addresses to Internet routers. CIDR was developed to cope with the surge in demand for IPv4 Internet addresses in the 1990s.


CoS (Class of Service)

See QoS


CSMA-CA (Carrier Sense Multiple Action - Collision Avoidance

The principle medium access method employed by IEEE 802.11 WLANs. It is a "listen before talk" method of minimising, but not eliminating, collisions caused by simultaneous transmission by multiple radios. IEEE 802.11 states collision avoidance method rather than collision detection must be used, because the standard employs half duplex radios which are capable of transmission and reception but not both simultaneously.

Unlike conventional wired Ethernet nodes, a WLAN station cannot detect a collision while transmitting. If a collision occurs, the transmitting station will not receive an ACKnowledge packet from the intended receive station. For this reason, ACK packets have a higher priority than all other network traffic. After completion of a data transmission, the receive station will begin transmission of the ACK packet before any other node can begin transmitting a new data packet. All other stations must wait a longer pseudo randomised period of time before transmitting. If an ACK packet is not received, the transmitting station will wait for a subsequent opportunity to retry transmission.


CSMA-CD (Carrier Sense Multiple Action - Collision Detection)

A method of managing traffic and reducing noise on an Ethernet network. A network device transmits data after detecting that a channel is available. However, if two devices transmit data simultaneously, the sending devices detect a collision and retransmit after a random time delay.


Cable Modem

This connects a home computer (or network of home computers) to a residential cable TV/Internet service. Cable modems are normally supplied by the cable / Internet service provider and can supply a 10 Mbps Ethernet connection for the home LAN, although cable modem service rarely if ever performs at those speeds.


Card and Socket Services

Software that works with the host computer operating system, enabling the WLAN adapter to interface with host computer configuration and power management functions.


Carrier Sense Multiple Action - Collision Avoidance (CSMA-CA)

See CSMA-CA


Carrier Sense Multiple Action - Collision Detection (CSMA-CD)

See CSMA-CD


Certificate

An attachment to an electronic message used for security purposes. The most common use of a digital certificate is to verify that a user sending a message is who he or she claims to be, and to provide the receiver with the means to encode a reply. An individual wishing to send an encrypted message applies for a digital certificate from a CA which then issues an encrypted digital certificate containing the applicant's public key and a variety of other identification information.


Certificate Authority (CA)

See CA


Channel

In wireless networks, radio carrier frequencies and appropriate bandwidths are assigned depending on the use to which the network is put, such a radio frequency being called a radio channel. Multiple channels are normally available within frequency bands to avoid interference.


Circuit switching

The process of setting up and keeping a circuit open between two or more users so that users have exclusive and full use of the circuit until the connection is released. The process involved in making a telephone call is an example of this.


Class of Service (CoS)

See QoS


Classless Inter-Domain Routing or Classless Internet Domain Routing (CIDR)

See CIDR


Client or Client devices

Any computer connected to a network that requests services (files, print capability) from another member of the network. Clients are end users. Wi-Fi client devices include PC Cards that slide into laptop computers, mini-PCI modules embedded in laptop computers and mobile computing devices, as well as USB and PCI/ISA bus Wi-Fi radios. Client devices usually communicate with hub devices like access points and gateways.


Cluster

A number of different implementations of shared computing resources. Typically, a cluster integrates the resources of two or more computing devices (that could otherwise function separately) together for some common purpose.


Collision

A term used to describe two colliding packets in an Ethernet network. Collisions are a part of normal Ethernet operation, but a sudden prolonged increase in the number of collisions can indicate a problem with a device, particularly if it is not accompanied by a general increase in traffic.


Collision avoidance

A network node characteristic for proactively detecting that it can transmit a signal without risking a collision, thereby ensuring a more reliable connection.


Continuously Aware Mode (CAM)

See CAM


Crossover cable

A special cable used for networking two computers without the use of a hub. Crossover cables may also be required for connecting a cable or DSL modem to a wireless gateway or access point. Instead of the signals transferring in parallel paths from one set of plugs to another, the signals "crossover." If an eight-wire cable was being used, for instance, the signal would start on pin one at one end of the cable and end up on pin eight at the other end. They "cross-over" from one side to the other.


Carrier Sense Multiple Action - Collision Avoidance (CSMA-CA)

See CSMA-CA


Carrier Sense Multiple Action - Collision Detection (CSMA-CD)

See CSMA-CD

[Danno]

D

DAPI (Device Application Programming Interface)

The software interface that facilitates communication of both data and control information between the Application Layer and HAPI, with support from System Support.


DAS (Distributed Antenna System)

A group of antennas networked together to provide radio coverage within a building such as a shopping centre. A DAS can provide WLAN, mobile coverage or both and is used as an alternative to Picocells.


DDNS (Dynamic Domain Name System or Server)

A service that maps Internet domain names to IP addresses but, unlike DNS that only works with static IP addresses, DDNS works with dynamic IP addresses, such as those assigned by an ISP or other DHCP server. DDNS is popular with home networkers, who typically receive dynamic, frequently-changing IP addresses from their service provider.


DES (Digital or Data Encryption Standard) and TripleDES (3DES)

A form of encryption used for data communications where both the sender and receiver must know the same secret key, which can be used to encrypt and decrypt the message, or to generate and verify a message authentication code. NETGEAR DES encryption uses a 56-bit key. 3DES, or "triple DES" on the other hand, is a variation on DES that uses a 168-bit key to provide more secure data transmission than DES. TripleDES is considered to be virtually unbreakable by security experts. It also requires a great deal more processing power, resulting in increased latency and decreased throughput unless hardware acceleration is provided.


DFS (Distributed File System)

A Microsoft technology that allows multiple servers and shared directories on a network to appear as a single network drive.


DHCP (Dynamic Host Configuration Protocol)

A protocol that assigns unique IP addresses to devices, then releases and renews these addresses as devices leave and re-join the network thus allowing a computer to join an IP-based network without having a pre-configured IP address. ISPs usually use DHCP to allow customers to join the Internet with minimum effort. Likewise, home network equipment like broadband routers offers DHCP support for added convenience in joining home computers to the LAN.

DHCP environments require a DHCP server set up with the appropriate configuration parameters for the given network. Key DHCP parameters include the range or "pool" of available IP addresses, the correct subnet masks, plus gateway and name server addresses. Devices running DHCP client software can then automatically retrieve these settings from DHCP servers as needed. Using DHCP on a network means system administrators do not need to configure these parameters individually for each client device.


DNS (Domain Name System or Server)

A program that translates URLs to IP addresses by accessing a database maintained on a collection of Internet servers. The program works behind the scenes to facilitate surfing the Web with alpha versus numeric addresses. A DNS server converts a name like mywebsite.com to a series of numbers like 107.22.55.26. Every website has its own specific IP address on the Internet.


DoS (Denial of Service)

A form of attacking computer systems over a network, DoS is normally a malicious attempt to render a networked system unusable, though often without permanently damaging it.

Denial of service relies on methods that exploit the weaknesses of network technology. For example, one common form of DoS is Ping of Death. Ping of Death attacks work by generating and sending certain kinds of network messages that are technically unsupported but known to cause problems for systems that receive them. Some DoS attacks like Ping of Death may crash or "hang" computers, others may simply fill or "flood" a network with useless data traffic, rendering systems incapable of acting on genuine requests.


DRAM (Dynamic Random Access Memory)

A type of inexpensive memory chip that requires power to store information. If the chip loses power, the information stored within will be lost.


DS (Direct Sequence)

DS generates a redundant bit pattern for each bit of data to be transmitted. Commonly referred to as a "chip" or "chipping code", this bit pattern numbers 10 chips to one per bit of information. This type of transmission enables high-speed transmission at 11 Mbps for applications such as wireless Internet access, video streaming, and large file transfers. Compared with frequency hopping, direct sequence has higher throughput, wider range and is upgradeable in the 2.4GHz band.


DSL (Digital Subscriber Line)

This provides high-speed networking over ordinary phone lines using digital modem technology. It integrates voice and data functionality and is "always on" unlike a normal telephone line which is only "on" when a call is made. The technology theoretically supports data rates of 8,448 Kbps (8.448 Mbps), although typical rates vary from 1,544 Kbps to 512 Kbps and sometimes as low as 90 Kbps.

DSL services target home and small business customers. However, the service only works over a limited physical distance and remains unavailable in many residential areas. The term "xDSL" generally refers to the complete family of related DSL technologies (ADSL, SDSL, VDSL etc) rather than any one specific implementation.


DVMRP (Distance-Vector Multicast Routing Protocol

A routing protocol used between routers in an intranet. This hop-based protocol describes a method of building multicast trees from the multicast source to all the receivers of the tree.


Data packet (also known as Packet)

A data packet is one unit of binary data capable of being routed through a computer network. To improve communication performance and reliability, each message sent between two network devices is often subdivided into packets by the underlying hardware and software.

Depending on the protocol(s) they need to support, packets are constructed in some standard packet format. Packet formats generally include a header, the body containing the message data (also known as the payload), and sometimes a footer (also known as the trailer). The packet header lists the destination of the packet (in IP packets, the destination IP address) and often indicates the length of the message data. The packet footer contains data that signifies the end of the packet, such as a special sequence of bits known as a magic number. Both the packet header and footer may contain error-checking information.
The receiving device is responsible for re-assembling individual packets into the original message, by stripping off the headers and footers and concatenating packets in the correct sequence.


Data Encryption Standard (DES)

See DES


Debug

The process of testing software or firmware in order to find errors or inconsistencies, then eliminating them.


Decryption

A mathematical operation that transforms data from "clear text" to "cipher text," which cannot be interpreted. Usually the mathematical operation requires that an alphanumeric key be supplied along with the clear text. The key and clear text are processed by the encryption operation, which leads to data scrambling that makes it secure. Decryption is the opposite of encryption being the mathematical operation that transforms cipher text to clear text. The same device, host computer or front-end processor, usually performs both encryption and decryption.


Denial of Service (DoS)

See DoS


Device Application Programming Interface (DAPI)

See DAPI


Dial up

A networking technology that provides PCs and other network devices access to a LAN or WAN via standard telephone lines. When the popularity of the Internet exploded in the 1990s, dial up was the most common form of Internet access due mainly to its low cost to setup. However, the performance of dial up networking is relatively poor due to the limitations of traditional modem technology usually offering less than 56 Kbps bandwidth. Many home users are currently replacing their dial up services with faster broadband technologies like DSL.


Diffserv (Differentiated Services)

A protocol for specifying and controlling network traffic by class so that certain types of traffic get precedence - for example, voice traffic, which requires a relatively uninterrupted flow of data, might get precedence over other kinds of traffic. Differentiated Services is the most advanced method for managing traffic in terms of what is called Class of Service (CoS).


Digital or Data Encryption Standard (DES) and TripleDES (3DES)

See DES


Digital Subscriber Line (DSL)

See DSL



Direct Sequence (DS)

See DS


Distance-Vector Multicast Routing Protocol (DVMRP)

See DVMRP


Distributed Antenna System (DAS)

See DAS


Distributed File System (DFS)

See DFS


Diversity: antenna

A type of antenna system that uses two antennas to maximise reception, improve transmission quality and reduce interference.


Domain Name

A descriptive name for an address or group of addresses on the Internet. Domain names are usually of the form of a registered entity name plus one of a number of predefined top level suffixes such as .com, .edu, .uk, etc. For example, in the address mail.NETGEAR.com, mail is a server name and NETGEAR.com is the domain.


Domain Name System or Server (DNS)

See DNS


Download

This involves the receipt of a file copied from a remote network location. Often, a person downloads files to their personal computer from a remote server computer. In Microsoft email networks, for example, people download their email from an Exchange server to their Outlook client. An upload involves sending a copy of a file to a remote network location. For example, Web publishers upload files to their Web server.

Sending files across a computer network does not necessarily constitute an upload or a download. The terms are more commonly used in client/server networking than in peer-to-peer networking.


Downstream

From the user's perspective, upstream network traffic flows away from the local computer toward the remote destination. Conversely, downstream traffic flows to the user's computer. Traffic on most networks flows in both upstream and downstream directions simultaneously, and often when data flows in one direction, network protocols often send control instructions (generally invisible to the user) in the opposite direction.

One way to generate upstream traffic is to upload files to a server or send an email message. Conversely, downloading files and receiving email generate downstream traffic. Typical Internet users create much more downstream than upstream traffic.


Driver

Software or firmware that controls a device. Every device, such as a printer, disk drive, or keyboard, must have a driver which acts as a translator between the device and programs that use the device, accepting generic commands from a program and then translating them into special commands for the device.


Dynamic Domain Name System or Server (DDNS)

See DDNS


Dynamic Host Configuration Protocol (DHCP)

See DHCP


Dynamic IP Addressing

See Static IP Addressing


Dynamic IP and Static IP Addressing

A Static IP address is an IP address that is "permanently" assigned to users when they first sign up for an Internet Service. Dynamically allocated IP addresses are assigned temporarily when a connection is made to the Internet and have a pre-determined time limit.


Dynamic Random Access Memory (DRAM)

See DRAM



Dynamic Routing

The ability of a router to forward data packets via a different route based on the current network conditions. For example, it can take account of traffic overload and faults and is thus much more flexible than static routing, which uses a fixed forwarding path.

[Danno]

E

EAP (Extensible Authentication Protocol)

A general protocol for authentication that supports multiple authentication methods. EAP, an extension to PPP, supports such authentication methods as token cards, Kerberos, one-time passwords, certificates, public key authentication and smart cards. In wireless communications using EAP, a user requests connection to a WLAN through an AP, which then requests the identity of the user and transmits that identity to an authentication server such as RADIUS. The server asks the AP for proof of identity, which the AP gets from the user and then sends back to the server to complete the authentication. EAP is defined by RFC 2284.


EAP-TTLS (Extensible Authentication Protocol Tunnelled Transport Layer Security)

See TTLS


EEPROM (Electronically Erasable Programmable Read Only Memory)

Also known as Flash, a re-programmable memory chip that does not require power to retain the information stored within, as opposed to DRAM. They are used to store configuration and boot-up information for systems such as routers and switches.


ESP (Encapsulating Security Payload)

ESP provides authentication, integrity, and confidentiality, which protect against data tampering and, most importantly, provide message content protection. It provides all encryption services in IPSec.

ESP has an option to perform authentication, called ESP authentication, which provides authentication and integrity for the payload and not for the IP header. The ESP header is inserted into the packet between the IP header and any subsequent packet contents. However, because ESP encrypts the data, the payload is changed. ESP does not encrypt the ESP header, nor does it encrypt the ESP authentication.


ESSID (Extended Short Set Identifier)

More commonly referred to as SSID, this is the identifying name of an 802.11 wireless network. When the correct ESSID is specified in a client setup it ensures that a connection is made to the required wireless network rather than another network in range. The ESSID can be called by different terms, such as Network Name, Preferred Network, SSID or Wireless LAN Service Area.

A 32-character unique identifier attached to the header of packets sent over a WLAN acts as a password when a device tries to connect or transmit over the WLAN. The ESSID differentiates one WLAN from another, so all access points and all devices attempting to connect to a specific WLAN must use the same ESSID.


EVDO (Evolution Data Only)

A high-speed network protocol used for wireless Internet data communications. EVDO supports up to 2.4 Mbps bandwidth using a set of radio frequency channels. The EVDO protocol supports asymmetric communications, allocating a majority of this bandwidth to downloads. Some CDMA mobile phones support EVDO. These phones are offered in several countries including the Sprint and Verizon networks in the USA. Additionally, various PCMCIA adapters and external modem hardware exists to enable laptops and handheld devices for EVDO.


Electronically Erasable Programmable Read Only Memory (EEPROM)

See EEPROM


Email

Short for 'electronic mail', this is a method of composing, sending, and receiving messages over computer networks. Most email systems today use the Internet, and email is one of the most popular uses of the Internet.


Encapsulating Security Payload (ESP)

See ESP


Encryption

See Decryption


Encryption Key

An alphanumeric series that enables data to be encrypted and then decrypted so it can be safely shared among members of a network. WEP uses an encryption key that automatically encrypts outgoing wireless data. On the receiving side, the same encryption key enables the computer to automatically decrypt the information so it can be read.


Endstation

A computer, printer, or server that is connected to a network.


Enhanced Data Encryption through TKIP

See TKIP


Enterprise-level User Authentication via 802.1x and EAP

WEP has almost no user authentication mechanism. To strengthen user authentication, Wi-Fi Protected Access implements 802.1x and the Extensible Authentication Protocol (EAP). Together, these implementations provide a framework for strong user authentication. This framework utilises a central authentication server, such as RADIUS, to authenticate each user on the network before they join it, and also employs "mutual authentication" so that the wireless user doesn't accidentally join a rogue network that might steal its network credentials.


Ethernet

International physical and data link layer technology for LANs. Basic 10BaseT networks offer a bandwidth of about 10 Mbps, Fast Ethernet about 100 Mbps and Gigabit Ethernet about 1000 Mbps. The run length of individual Ethernet cables is limited to roughly 100 meters, but Ethernet can be bridged to easily network entire schools or office buildings. Higher level network protocols like Internet Protocol (IP) use Ethernet as their transmission medium. Data travels over Ethernet inside protocol units called frames.


Evolution Data Only (EVDO)

See EVDO


Extended Range (XR)

See XR


Extended Service Set (ESS)

See BSS


Extended Short Set Identifier (ESSID)

See ESSID


Extranet

A computer network that allows controlled access from the outside for specific business or educational purposes. Extranets are extensions to, or segments of, private intranet networks that have been built in many corporations for information sharing and ecommerce. Most extranets use the Internet as the entry point for outsiders, a firewall configuration to limit access, and a secure protocol for authenticating users.


Extensible Authentication Protocol (EAP)

See EAP

[Danno]

F

FHSS (Frequency Hopping Spread Spectrum)

A radio transmission technology which uses a narrowband carrier that changes frequency in a pattern known to both transmitter and receiver. Because the signal "hops," it is highly secure, provides great coverage, is less susceptible to interference and has robust throughput. There are 79 channels in a 2.4GHz ISM band, each channel occupying 1MHz of bandwidth. A minimum hop rate of 2.5 hops per channel per second is required in the United States. Frequency hopping technology is recognised as superior to direct sequence in terms of echo resistance, interference immunity, cost and ease-of-installation. To date, there has also been a greater selection of WLAN products from which to choose.


FQDN (Fully qualified domain name)

This consists of a host and domain name, including a top-level domain. For example, http://www.netgear.com is a fully qualified domain name: 'www' is the host, 'netgear' is the second-level domain, and '.com' is the top level domain.


FQHN (Fully qualified host name)

Either the FQDN of a host, or the numeric IP address of a host.


FTP (File Transfer Protocol)

FTP allows you to transfer files between computers on the Internet. Technically, FTP is a simple network protocol based on IP, but many also use the term "FTP" to refer to this type of file sharing service. The FTP service is based on client/server architecture where an FTP client program initiates a connection to a remote computer running FTP server software, then after the connection is established, the client can choose to send and/or receive copies of files, singly or in groups. To connect to an FTP server, a client generally requires a username and password as set by the administrator of the server.


Fast Ethernet

Fast Ethernet supports a maximum data rate of 100 Mbps. It is so named because original Ethernet technology supported only 10 Mbps. Fast Ethernet began to be widely deployed in the mid-1990s as the need for greater LAN performance became critical to universities and businesses.

A key element of Fast Ethernet's success was its ability to coexist with existing network installations. Today, many network adapters support both traditional and Fast Ethernet. These so-called "10/100" adapters can usually sense the speed of the line automatically and adjust accordingly. Just as Fast Ethernet improved on traditional Ethernet, Gigabit Ethernet improves on Fast Ethernet, offering rates up to 1000 Mbps instead of 100 Mbps.


Fault isolation

A technique for identifying and alerting administrators about connections (such as those associated with switch ports) that are experiencing congestion or failure, or exceeding an administrator-defined threshold.


Filtering

The process of screening a packet for certain characteristics, such as source address, destination address, or protocol. Filtering is used to determine whether traffic is to be forwarded, and can also prevent unauthorised access to a network or network devices.


Firewall

A system that secures a network and prevents access by unauthorised users. Firewalls can be software, hardware or a combination of both. Firewalls can prevent unrestricted access into a network, as well as restrict data from flowing out of a network.

Perhaps the most common form of network firewall is a proxy server. Proxy servers act as an intermediary between intranet and Internet computers by receiving and selectively blocking data packets at the network boundary. These network firewalls also provide an extra measure of safety by hiding internal LAN addresses from the outside Internet. In a proxy server firewall environment, network requests from multiple clients appear to the outsider as all coming from the same proxy server address.


Firmware

In a home computer network, firmware is embedded software inside a router. It implements a portion of the network protocols, security mechanisms and administrative capabilities of the hardware device. Both wired routers and wireless routers contain firmware which exists in read-only memory chips contained inside the router. Firmware does not get erased when a router is powered off nor can it be altered externally by hackers.

Firmware is designed to be freely upgraded by homeowners later as enhancements become available. Updating a router's firmware can increase its performance, security and/or reliability depending on the nature of the enhancements provided. Firmware upgrades generally need to be done infrequently, however.


Flash

See EEPROM


Flood

A type of DoS attack that sends large amounts of ICMP packets to a device in order to attempt to crash the TCP/IP stack on the device and cause it to stop responding to TCP/IP requests.


Flow control

A congestion control mechanism. Congestion is caused by devices sending traffic to already overloaded ports on a switch. Flow control prevents packet loss and temporarily inhibits devices from generating more traffic until the period of congestion ends.


Forwarding

The process of sending a packet toward its destination using a networking device.


Frequency Hopping Spread Spectrum(FHSS)

See FHSS


FTP (File Transfer Protocol)

See FTP


Full-duplex

A system that allows packets to be transmitted and received at the same time and, in effect, doubles the potential throughput of a link.


Fully qualified domain name (FQDN)

See FQDN


Fully qualified host name (FQHN)

See FQHN

[Danno]

G

Gbps, Kbps / kbps, Mbps (Also Known As: Kb/sec, Kb/s, Mb/sec, Mb/s, Gb/sec, Gb/s)

One kilobit per second (Kbps) equals 1000 bits per second (bps). Kbps is also written as "kbps". Likewise, one megabit per second (Mbps) equals one million bps and one Gigabit equals one billion bps.

Network performance is best measured in bps, but sometimes numbers are given in bytes per second (Bps). Then, one KBps equals one kilobyte per second, one MBps equals one megabyte per second, and GBps equals one gigabyte per second.


GBIC (Gigabit Interface Converter)

A device used to convert electrical signals into optical signals and vice versa.


GBIC Module

A transceiver that converts serial electric signals to serial optical signals and vice versa. For networking, GBIC has come to mean a standards-based module that will provide a Gigabit Ethernet port when inserted into a GBIC slot. GBIC's provide a variety of interfaces including 1000Base-T, 1000Base-SX and 1000Base-LX. A GBIC module allows users the option of using either optical or copper connections. GBICs also are hot-swappable, which adds to the ease of upgrading electro-optical communication networks.


Gain, dBd

Antenna gain, expressed in decibels referenced to a half wave dipole.


Gain, dBi

Antenna gain, expressed in decibels referenced to a theoretical isotropic radiator.


Gain, dBic

Antenna gain, expressed in decibels referenced to a theoretical isotropic radiator that is circularly polarised.


GHz (Gigahertz)

The international unit for frequency is the Hertz (Hz), which is equivalent to the older unit of cycles per second. One Gigahertz (GHz) is one billion Hertz. Microwave ovens typically operate at a frequency of 2.45 GHz. Similarly Kilohertz (KHz) and Megahertz (MHz).


GUI (Graphical User Interface)

A user interface that represents commands, files, and windows as icons that users can access and manipulate using a mouse or other pointing device.


Gateway

In the wireless world, a gateway is an access point with additional software capabilities such as providing NAT and DHCP. Gateways may also provide VPN support, roaming, firewalls, various levels of security, etc.

A network gateway is an internetworking system, a system that joins two networks together. A network gateway can be implemented completely in software, completely in hardware, or as a combination of the two. Depending on their implementation, network gateways can operate at any level of the OSI model from application protocols to low-level signalling. Because a network gateway by definition appears at the edge of a network, related functionality like firewalls tends to be installed on the network gateway.


Gigabit Ethernet (1000 Mbps Ethernet)

An extension to the family of Ethernet computer networking and communication standards. The Gigabit Ethernet standard supports a theoretical maximum data rate of 1000 Mbps on ordinary twisted pair copper cable, specifically the CAT5e and CAT6 cabling standards.


Gigabit Interface Converter (GBIC)

See GBIC


Gigabyte (GB)

A kilobyte equals 1024 (or 210) bytes. Likewise, a megabyte (MB) equals 1024 KB or 220 bytes and a gigabyte (GB) equals 1024 MB or 230 bytes.

The meaning of the words kilobyte, megabyte, and gigabyte change when they are used in the context of network data rates. Then, a rate of one kilobyte per second (KBps) equals 1000 (not 1024) bytes per second, one megabyte per second (MBps) equals one million (106, not 220) bytes per second and one gigabyte per second (GBps) equals one billion (109, not 230) bytes per second. To avoid some of this confusion, networkers typically measure data rates in bits per second (bps) rather than bytes per second (Bps) and use the terms kilobyte, megabyte, and gigabyte only when referring to disk space.


Graphical User Interface (GUI)

See GUI

[Danno]

H

HAPI (Hardware Abstraction Programming Interface)

The module that contains the NP specific software that interacts with the hardware.


HTML (Hypertext Markup Language)

A markup language based on, but simpler than, SGML used to annotate hypertext documents for publication on the World Wide Web.


HTTP (Hypertext Transport Protocol)

An application layer network protocol built on top of TCP, allowing Web browsers and Web servers to communicate and transfer HTML documents.


HTTPS (Secure Hyper Text Transport Protocol or HTTP over SSL)

A variant of HTTP that encrypts messages for security. When logging on to secure Web sites, the URL starts with HTTPS rather than HTTP, the 'S' indicating a secure connection.


Hz (hertz)

The international unit for measuring frequency, equivalent to the older unit of cycles per second. One megahertz (MHz) is one million hertz. One gigahertz (GHz) is one billion hertz. Wireless 802.11b LANs operate at 2.4 GHz.


Half-duplex

A system that allows packets to be transmitted and received, but not simultaneously, as opposed to full-duplex.


Hardware Abstraction Programming Interface (HAPI)

See HAPI


Hertz (Hz)

See Hz


Hop Count

The number of routers that a data packet passes through on its way to its destination. In computer networking, a hop represents one portion of the path between source and destination. When communicating over the Internet, for example, data passes through a number of intermediate devices (like routers) rather than flowing directly over a single wire. Each such device causes data to "hop" between one point-to-point network connection and another.

In networking, the hop count represents the total number of devices a packet passes through. Generally speaking, the more hops a packet traverses to reach its destination, the greater the transmission delay incurred.

Network utilities like Ping can be used to determine the hop count to a specific destination. Ping generates packets that include a field reserved for the hop count. Each time a capable device receives these packets, that device modifies the packet, incrementing the hop count by one. In addition, the device compares the hop count against a predetermined limit and discards the packet if its hop count is too high. This prevents packets from endlessly bouncing around the network due to routing errors. Both routers and bridges are capable of managing hop counts, but other types of intermediate devices, like hubs, are not.


Hot Spot (also referred to as Public Access Location)

Any location where Wi-Fi network access (usually Internet access) is made publicly available. Hotspots can be found in airports, hotels, coffee shops, and other places where business people tend to congregate and are considered a valuable productivity tool for business travellers and other frequent users of network services.

Technically speaking, hotspots consist of one or several WAPs installed inside buildings and/or adjoining outdoor areas. These WAPs are typically networked to printers and/or a shared high-speed Internet connection. Some hotspots require special application software to be installed on the Wi-Fi client, primarily for billing and security purposes, but others require no configuration other than knowledge of the network name (SSID).


Hot-swappable

The ability to add devices to and remove them from a computer while it is running with the operating system automatically recognising the change.



Hub

A multiport device used to connect PCs to a network via Ethernet cabling or via Wi-Fi. Wired hubs can have numerous ports and can transmit data at speeds ranging from 10 Mbps to multigigabyte speeds per second. A hub transmits packets it receives to all the connected ports. A small wired hub may only connect 4 computers whereas a large hub can connect 48 or more and wireless hubs hundreds.

Most hubs manufactured today support the Ethernet standard. Non-Ethernet hubs (Token Ring, for example) also exist, but Ethernet is always used in home networking. Technically speaking, hubs operate as Layer 2 devices in the OSI model.


HyperText Markup Language (HTML)

See HTML


HyperText Transport Protocol (HTTP)

See HTTP

[Danno]

I

IANA (Internet Assigned Numbers Authority)

One of the primary governing bodies for Internet networking, IANA oversees three key aspects of the Internet:

* top-level domains (the trailing portion of Web domain names such as .com and .org)
* IP address allocation
* Port number assignments


ICMP (Internet Control Message Protocol)

A network protocol useful in IP network management and administration, ICMP is a required element of IP implementations. It is a control protocol, meaning that it does not carry application data, but rather information about the status of the network itself. ICMP can be used to report:

* errors in the underlying communications of network applications
* availability of remote hosts
* network congestion
* identification of intermediate "hops" between a given source and destination


ICS (Internet Connection Sharing)

Allows a local network of Windows computers to share a single Internet connection. The feature has been included as part of all Windows releases from 98 on, but it is not available as a separate installable program. It incorporates a DHCP server that allows clients to obtain their local addresses automatically rather than needing to be set manually.


ID (Intrusion detection)

A type of security management system for computers and networks. An ID system gathers and analyses information from various areas within a computer or a network to identify possible security breaches, which include both intrusions (attacks from outside the organisation) and misuse (attacks from within the organisation).


IEEE (Institute of Electrical and Electronics Engineers)

A U.S. membership organisation (http://www.ieee.org) that includes engineers, scientists and students in electronics and allied fields. It has more than 300,000 members and is involved with setting standards for computers and communications.


IEEE 802.11 (Also see 802)

One of a set of LAN specifications from the IEEE which defines the standard for wireless LANs encompassing three incompatible (non-interoperable) technologies: Frequency Hopping Spread Spectrum (FHSS), Direct Sequence Spread Spectrum (DSSS) and Infrared.


IETF (Internet Engineering Task Force)

An organisation responsible for providing engineering solutions for TCP/IP networks. In the network management area, this group is responsible for the development of the SNMP protocol.


IGMP (Internet Group Multicast Protocol)

The standard for IP Multicasting on the Internet, IGMP is used to establish host memberships in particular multicast groups on a single network. Multicasts are utilised to send traffic, such as online video training, to multiple users simultaneously, without flooding the traffic to users that do not want it, thereby saving network bandwidth. With support for IGMP snooping, the switch intelligently transmits the multicast stream to only those interfaces that request the stream. This saves precious bandwidth and ensures efficiency in the rest of the network.


IKE (Internet Key Exchange)

A negotiation and key exchange protocol specified by the IETF. An IKE security association automatically negotiates encryption and authentication keys. With IKE, an initial exchange authenticates the VPN session and automatically negotiates keys that will be used to pass IP traffic.


IMS (IP Multimedia Subsystem)

A unified architecture based on IETF Internet protocols that can support a range of IP-based services for both packet and circuit switched networks employing a range of different wireless and fixed access mechanisms. Because IMS is technology independent, it supports IP to IP sessions over fixed line, 802.11, 802.15 and all mobile technologies. IMS is a standardised reference architecture that consists of session control, connection control and an applications services framework along with subscriber and services data.


IP (Internet Protocol)

The method, or protocol, by which data is sent from one computer to another over the Internet. Data travels in the form of packets, each packet including both a header (that specifies source, destination, and other information about the data) and the message data itself. IP specifies the format and addressing scheme for each packet.


IPv4

An outdated version of the IP protocol using a 32-bit addressing scheme, represented by four 8-bit (0-255) numbers such as 123.3.12.255. It is still widely used but, because of it's limitations as regards number of possible IP addresses, security etc. it is being replaced by IPv6.


IPv6

A replacement for IPv4, IPv6 is backward compatible with and is designed to fix the shortcomings of IPv4, such as data security and maximum number of user addresses. It increases the address space from 32 to 128 bits, providing for an unlimited number of networks and systems. It also supports quality of service (QoS) parameters for real-time audio and video.


IP address

A 32-bit number that identifies each sender or receiver of information that is sent across the Internet. An IP address has two parts: an identifier of a particular network on the Internet and an identifier of the particular device (which can be a server or a workstation) within that network.


IPConfig

A Windows 2000/XP utility program that displays the IP address for a networked device.


IP Multimedia Subsystem (IMS)

See IMS


IP multicast

Sending data from one source to specific multiple destinations on the Internet. For large amounts of data, IP Multicast is more efficient than normal Internet transmissions, because the server can send a message to many recipients simultaneously. Unlike traditional Internet traffic that requires separate connections for each source-destination pair, IP multicasting allows many recipients to share the same source. This means that just one set of packets is transmitted for all the destinations.


IPSec Protocol (Internet Protocol Security)

A robust VPN standard that covers authentication and encryption of data traffic over the Internet. VPN technology employing IPSec will encrypt all outgoing data and decrypt all incoming data so that a public network can be used, like the internet, as transportation media. The algorithms IPSec uses produce a unique and unforgeable identifier for each packet, which is a data equivalent of a fingerprint. This fingerprint allows the device to determine if a packet has been tampered with. Furthermore, packets that are not authenticated are discarded and not delivered to the intended receiver.


IP telephony

A technology that converts analogue voice into digital data packets to support telephony over IP networks. So-called "Voice over IP" (VoIP) solutions today support IP telephony. The deployment of Internet telephony allows both voice and data to share the same networks thus allowing the telecommunications industry to move away from the need to have numerous different networks.


IP Video Surveillance

IP-based video surveillance offers cost-efficient and future-proof solutions for security, industrial and remote monitoring applications. Connecting directly to the network, IP cameras can distribute high-quality, digital video streams over any IP network, being local or the Internet, using wired or wireless connections.


ISDN (Integrated Services Digital Network)

A network technology that supports transfer of simultaneous voice and data traffic. Similar to DSL in this respect, an ISDN Internet service works over ordinary telephone lines. ISDN Internet service generally supports data rates of 128 Kbps and emerged as an alternative to traditional dial-up networking during the 1990s. The much higher speeds supported by DSL technologies have diminished the importance of ISDN.


ISO (International Standards Organisation) Network Model

A data network model developed by the ISO, called Open Systems Interconnection (OSI), that consists of seven different levels, or layers. Each layer uses and builds on the services provided by those below it. By standardising these layers, and the interfaces between them, different portions of a given protocol can be modified or changed as technologies advance or systems requirements are altered. The seven layers are:

Layer 1 - Physical
Layer 2 - Data Link
Layer 3 - Network
Layer 4 - Transport
Layer 5 - Session
Layer 6 - Presentation
Layer 7 - Application

The upper layers represent software that implements network services like encryption and connection management, the lower layers implement more basic, hardware-oriented functions like routing, addressing, and flow control. The IEEE 802.11 Standard encompasses the physical layer and the lower portion of the data link layer.


ISP

A company that supplies Internet connectivity to home and business customers. ISPs support one or more forms of Internet access, ranging from traditional modem dial-up through DSL and cable modem broadband service to dedicated wideband connections. In addition to basic connectivity, many ISPs also offer related Internet services like email, Web hosting and access to software tools.


Inbound / Outbound Rules

Many devices, such as routers, are configurable in respect of how they handle both incoming and outgoing traffic. Configuration of such devices allows rules to be set as to how different types of traffic are handled or distributed. Rules can also be set as to how traffic to or from specific IP addresses is handled.


Infrastructure Mode

A client setting providing connectivity to an AP. As compared to Ad-Hoc mode, whereby PCs communicate directly with each other, clients set in Infrastructure Mode all pass data through a central AP. The AP not only mediates wireless network traffic in the immediate neighbourhood, but also provides communication with the wired network.


Institute of Electrical and Electronics Engineers (IEEE)

See IEEE


International Standards Organisation (ISO)

See ISO


Internet

The term refers to the global network of public computers running IP. The Internet supports the public WWW and many special-purpose client/server software systems. Internet technology also supports many private corporate intranets and private home LANs.

The term "Internet" was originally coined in the 1970s. At that time, only the very meagre beginnings of a public global network were in place. Throughout the 1970s, 1980s, and 1990s, a number of smaller national networks like ARPANET, BITNET, CSNET, and NSFNET evolved, merged, or dissolved, then finally joined with non-US networks to form the global Internet.


Internet Assigned Numbers Authority (IANA)

See IANA


Internet Connection Sharing (ICS)

See ICS


Internet Control Message Protocol (ICMP)

See ICMP


Internet Engineering Task Force (IETF)

See IETF


Internet Group Management Protocol (IGMP)

See IGMP


Internet Key Exchange (IKE)

See IKE


Internet Phone

An Internet phone can be a small phone or a multimedia PC with a microphone, speaker, and modem. It has the ability to convert the output from a standard phone to IP.


Internet Protocol (IP)

See IP


Internet Protocol (IP) address

See IP address


Interoperability

The ability of hardware and software from different suppliers to operate together in a network.


Intranet

The generic term for a collection of private computer networks within an organisation based on the technology of the Internet. Intranets are communication tools designed to enable easy information sharing within workgroups. Besides email and groupware applications, an intranet generally incorporates internal Web sites, documents, and/or databases to disseminate information.


Intrusion detection (ID)

See ID


Internet Protocol Security (IPSec)

See IPSec


Integrated Services Digital Network (ISDN)

See ISDN


International Standards Organisation (ISO) Network Model

See ISO Network Model

[Danno]

J

[Danno]

K

Kbps (Kilobit per second)

See Gbps, Kbps / kbps, Mbps


Kerberos

A widely deployed security protocol that was developed at the Massachusetts Institute of Technology (MIT) to authenticate users and clients in a wired network environment and to securely distribute encryption keys.


Kilobyte (KB)

See Gigabyte

[Danno]

L

LAN (Local Area Network)

A LAN supplies networking capability to a group of computers in close proximity to each other such as in an office building, a school, or a home. It comprises endstations (such as PCs, printers, servers) and network devices (hubs and switches) plus the means of linking these in wired or wireless form. A LAN is useful for sharing resources like files, printers, games or other applications. A LAN in turn often connects to other LANs, and to the Internet or other WAN.


LDAP (Lightweight Directory Access Protocol)

A set of protocols for accessing network directories. Network directories are specialised databases that store information about devices, applications, people and other aspects of a computer network. LDAP is based on the standards contained within the X.500 standard, but is significantly simpler. Unlike X.500, LDAP supports TCP/IP, which is necessary for any type of Internet access.


LEAP (Lightweight Extensible Authentication Protocol)

An early version of EAP which has since been replaced.


Layer

A protocol that interacts with other protocols as part of an overall transmission system.


Learning

The bridge examines the Layer 2 source addresses of every frame on the attached networks (called listening) and then maintains a table, or cache, of which MAC addresses are attached to each of its ports.


Lightweight Directory Access Protocol (LDAP)

See LDAP


Lightweight Extensible Authentication Protocol (LEAP)

See LEAP


Link Aggregation (Trunking)

Link Aggregation provides the ability to logically group a number of physical interfaces together to form a single interface. This important feature helps circumvent possible network bottlenecks by aggregating bandwidth for crucial network connections. In addition to adding throughput, link aggregation also provides a form of redundancy by ensuring that even if one link fails, network traffic will still be forwarded over the remaining links in the aggregation group.


Link State

In routing protocols, the declared information about the available interfaces and available neighbours of a router or network. The protocol's topological database is formed from the collected link-state declarations.


Linux

An open and free computer operating system based on Unix.


Load balancing

The ability to distribute traffic across various ports of a device, such as a switch, to provide efficient, optimised traffic throughout the network.


Local Area Network (LAN)

See LAN


Logs

Records of network or individual device activities. These activities can include things such as access records and errors.


Loop

An event that occurs when two network devices are connected by more than one path, thereby causing packets to repeatedly cycle around the network and not reach their destination.


Loopback

A type of diagnostic test in which the transmitted signal is returned to the sending device after passing through all or part of a communications link or network. It is used mainly to help to identify a faulty device or network link.

[Danno]

M

MAC (Media Access Control)

A protocol specified by the IEEE for determining which devices have access to a network. Every wireless 802.11 device has its own specific MAC address hard-coded into it. This unique identifier can be used to provide security for wireless networks. When a network uses a MAC table, only the 802.11 radios that have had their MAC addresses added to that network's MAC table will be able to get onto the network. MAC works at the lower sublayer of the data link layer (Layer 2) of the OSI model.


MAC address

The hardware or physical address assigned to devices in a network as part of the MAC protocol.


MAN (Metropolitan Area Network)

A term used to describe a network larger than a LAN but smaller than a WAN, usually in urban areas.


Mbps

See Gbps, Kbps / kbps, Mbps


MDI/MDIX (Media Dependant Interface-Crossover)

In cable wiring, the concept of transmit and receive are from the perspective of the PC, which is wired as a MDI. In MDI wiring, a PC transmits on pins 1 and 2. At the hub, switch, router, or access point, the perspective is reversed, and the hub receives on pins 1 and 2. This wiring is referred to as MDI-X.


MIB (Management Information Base)

When SNMP devices send SNMP messages to the management console (the device managing SNMP messages), it stores information in the MIB.


MIMO (Multiple Input Multiple Output)

A technique using multiple antennas which makes use of the Multipath phenomenon to create virtual channels thus improving speed and coverage of an AP.


MPLS (Multi-Protocol Label Switching)

An initiative that integrates Layer 2 information about network links (bandwidth, latency and utilisation) into Layer 3 (IP) within a particular autonomous system in order to simplify and improve IP-packet exchange. MPLS gives network operators a great deal of flexibility to divert and route traffic around link failures, congestion, and bottlenecks. From a QoS standpoint, ISPs are better able to manage different kinds of data streams based on priority and service plan. For instance, those who subscribe to a premium service plan, or those who receive a lot of streaming media or high-bandwidth content can see minimal latency and packet loss. When packets enter into a MPLS-based network, Label Edge Routers (LERs) give them a label (identifier). These labels not only contain information based on the routing table entry (i.e., destination, bandwidth, delay, and other metrics), but also refer to the IP header field (source IP address), Layer 4 socket number information, and differentiated service. Once this classification is complete and mapped, different packets are assigned to corresponding Labelled Switch Paths (LSPs), where Label Switch Routers (LSRs) place outgoing labels on the packets. With these LSPs, network operators can divert and route traffic based on data-stream type and Internet-access customer.


MTBF (Mean Time between Failures)

The typical time a device will function before failing, calculated using known failure rates of components that are used in a system.


MT-RJ connector

A type of fibre-optic cable plug that is similar in shape and concept to a standard telephone plug, enabling duplex fibre-optic cables to be plugged into compatible devices as easily as plugging in a telephone cable.


MTU

The MTU is a limit, expressed in bytes, on the size of data sent over a network. It is the maximum size of a single unit (e.g., an Ethernet frame) of digital communications.


Management Information Base (MIB)

See MIB


Mean Time Between Failure (MTBF)

See MTBF


Media Access Control (MAC)

See MAC


Megabyte (MB)

See Gigabyte


Megahertz (MHz)

The unit of frequency used to measure the clock speed of a computer. One megahertz represents one million cycles per second.


Mesh Networks

Also called mesh topology, mesh is a network topology in which devices are connected with many redundant interconnections between network nodes. In a full mesh topology every node has a direct connection to every other node in the network. Mesh networks may be wired or wireless. In a wireless mesh example, each of the spheres below represents a mesh router. Corporate servers and printers may be shared by attaching to each mesh router. For wireless access to the mesh, an access point must be attached to any one of the mesh routers.


Metropolitan Area Network (MAN)

See MAN


Mobile Unit Mode

In this mode, the WLAN adapter connects to an AP or another WLAN installed system, allowing the device to roam freely between AP cells in the network. Mobile units appear as network nodes to other devices.


Modem

An acronym for "Modulator Demodulator". Traditionally, a modem converts data between the analogue form used on telephone lines and the digital form used in computers for the purpose of computer-to-computer communication. Standard modems can transmit data at a maximum rate of 56,000 bits per second (bps) or 56kbps. However, inherent limitations of the phone system translate to modem speeds of 33.6kbps or lower in practice.

More recently, modems for cable and DSL service have come to be known as digital modems and those used for traditional dial-up networking as analogue modems. The terminology is somewhat misleading as modems all involve analogue signalling. Nonetheless, broadband cable and DSL modems achieve dramatically higher network speeds than traditional modems.


Multicast

See IP Multicast


Multicasting

To transmit a message to specific recipients across a network. A simple example of multicasting is sending an e-mail message to a mailing list. Note that multicasting refers to sending a message to a select group whereas broadcasting refers to sending a message to everyone connected to a network.


Multicast OSPF

With a MOSPF specification, an IP Multicast packet is routed based both on the packet's source and its multicast destination (commonly referred to as source/destination routing). As it is routed, the multicast packet follows a shortest path to each multicast destination.


Multimode devices

A term which, in this context, refers to wireless products which are able to operate in a number of different technical environments such as WLAN and mobile technologies like GSM.


Multipath Fading

A type of fading caused by signals taking different paths from the transmitter to the receiver and, consequently, interfering with each other.


MIMO (Multiple Input Multiple Output)

See MIMO


Multiplexing

A function within a layer that interleaves the information from multiple connections into one connection.


Multi-Protocol Label Switching (MPLS)

See MPLS

[Danno]

N

NAK (Negative Acknowledgement)

See ACK


NAS (Network Attached Storage)

A system allowing files to be stored and retrieved across a computer network having a dedicated "server" which authenticates clients and manages file operations in much the same manner as traditional file servers, through well-established network protocols like NFS and CIFS/SMB. NAS systems attempt to reduce the cost associated with traditional file servers and tend to be easier to manage than a file server. Not to be confused with the related term SAN, NAS devices are just one type of entity that can exist on a SAN.


NAT (Network Address Translation)

A network capability that enables a houseful of computers to dynamically share a single incoming IP address supplied by an Internet Service Provider (ISP) from a dial-up, cable or xDSL connection. NAT takes the single incoming IP address and creates new IP addresses for each client computer on the network. NAT is used in the router to prevent hacking into the local area network (LAN).


NIC (Network Interface Card)

A type of PC adapter card e.g. a PCI or PCMCIA card, that either works without wires (Wi-Fi) or attaches to a network cable to provide two-way communication between the computer and network devices such as a hub or switch.


NTP (Network Time Protocol)

An Internet standard protocol, built on top of TCP/IP that assures accurate synchronisation (to the millisecond) of computer clock times in a network of computers. NTP is designed to be highly fault-tolerant and scalable.


Nagle algorithm

Named after its inventor John Nagle, this was designed to reduce LAN and other network congestion by making TCP applications run more efficiently. It works by aggregating data on the sending side of TCP applications accumulating sequences of small messages into larger TCP packets before data reaches the network, thereby preventing the generation of unnecessarily large numbers of small packets.


NetBIOS (Network Basic Input Output System)

An API for sharing services and information on LANs. It provides for communication between stations of a network where each station is given an alphanumeric name, 16 characters in length.


Netmask

Combined with the IP address, the IP Subnet Mask allows a device to know which other addresses are local to it and which must be reached through a gateway or router. It is a number that explains which part of an IP address comprises the network address and which part is the host address on that network.


NetWare

An operating system developed by Novell, Inc that was one of the first software products built for the networking of PCs. NetWare emphasises file and print serving capabilities and the predominant use of NetWare is as a LAN server.


Network

Two or more computers or other devices, such as printers, that are linked in order to communicate with each other.


Network Address Translation (NAT)

See NAT


Network Attached Storage (NAS)

See NAS


Network name

During the installation process for most wireless networks it is necessary to enter the network name or SSID.


Network Interface Card (NIC)

See NIC


Network Time Protocol (NTP)

See NTP


Node

On an IP network, a node is any device such as a switch or a router with an IP address.

[Danno]

O

OBSAI (Open Base Station Architecture Initiative)

An organisation of base station and component manufacturers creating specifications for modular wireless base station architecture. The latest specifications include WiMax as well as mobile.


OFDM (Orthogonal Frequency Division Multiplexing)

A modulation technique for transmitting large amounts of digital data over radio, OFDM works by splitting the radio signal into multiple smaller sub-signals which are then transmitted simultaneously at different frequencies. It is used in 802.11a, 802.16 and WiMax.


OSAPI (Operating System Application Programming Interface)

A module within the System Support software that provides a set of interfaces to the Operating System support functions.


OSI (Open Systems Interconnection)

See ISO


OSPF (Open Shortest Path First)

A link-state (algorithm used by the router to determine the current topology of a network), Interior Gateway (distributes routing information between routers belonging to a single Autonomous System) routing protocol. This protocol's algorithm determines the shortest path from its router to all the other routers in the network. This protocol has replaced RIP on the Internet.


Open Base Station Architecture Initiative (OBSAI)

See OBSAI


Open Shortest Path First (OSPF)

See OSPF


Open Systems Interconnection (OSI)

See OSI


Operating System Application Programming Interface (OSAPI)

See OSAPI


Orthogonal Frequency Division Multiplexing (OFDM)

See OFDM

[Danno]

P

PAL (Public Access Location)

See Hotspot


PAN (Personal Area Network) also called Piconet

A network of devices connected in an ad hoc fashion using Bluetooth technology which is formed when at least two devices, such as a portable PC and a mobile phone, connect. A PAN can support up to eight devices and one device acts as the master while the others act as slaves for the duration of the connection.


PASV

An alternative mode for establishing FTP connections, PASV mode is designed for FTP clients behind firewalls. PASV mode works by allowing FTP clients to initiate sending of both control and data messages. Ordinarily, only FTP servers initiate the data requests. Because many client firewalls reject incoming messages like these FTP requests, PASV mode makes FTP "firewall-friendly."


PC card

See PCMCIA


PCI adapter

A high-performance I/O computer bus used internally on most computers. Other bus types include ISA and AGP. PCIs and other computer buses enable the addition of internal cards that provide services and features not supported by the motherboard or other connectors.


PCMCIA (Personal Computer Memory Card International Association)

A removable card that fits into a PCMCIA standard slot primarily in PCs, portable computers, PDAs and laptops. The slot can be used for Wi-Fi cards, memory cards, modems, NICs, hard drives, etc.


PDA (Personal Digital Assistant)

A handheld computer or electronic personal organiser.


PDU (Protocol Data Unit)

A packet of data passed across a network. The term implies a specific layer of the OSI model and a specific protocol.


PHY

The lowest, PHYsical, layer within the OSI Network Model. It deals primarily with transmission of the raw bit stream over the transport medium. In the case of wireless LANs, the transport medium is free space. The PHY defines parameters such as data rates, modulation method, signalling parameters, transmitter/receiver synchronisation, etc.


PKI (Public Key Infrastructure)

A system of digital certificates, Certificate Authorities, and other registration authorities that verify and authenticate the validity of each party involved in an Internet transaction.


PMP (Point-to-multipoint)

A term used mainly in wireless networks where there is a central endpoint (base station) and peripheral endpoints (remote stations) in which data originating from the central endpoint is received by all other endpoints but data originating from the peripheral endpoints is received only by the central endpoint.


POE (Power over Ethernet)

The ability to provide power to wired networked devices over the LAN cabling without needing a separate power supply system.


POP (Post Office Protocol)

The standard protocol for receiving e-mail. POP3 is the most recent version of the client/server protocol in which e-mail is received and held for you by your Internet server.


PPP (Point-to-Point Protocol)

Provides a standard means of encapsulating data packets sent over a single-channel WAN link. It is the standard WAN encapsulation protocol for the interoperability of bridges and routers. PPP is also supported in workstations, allowing direct dial-up access from a personal computer to a corporate LAN or ISP.


PPPoE (Point to Point Protocol over Ethernet)

Combines the Ethernet and PPP standards specifically for use with modems capable of broadband connectivity. PPPoE itself is documented in RFC 2516. When used with DSL, PPPoE can require additional software that establishes a network session via dial-up. Some DSL routers include built-in PPPoE support to eliminate the need for software.


PSK (Pre shared key)

Passwords or encryption keys that are manually entered (typed or entered via floppy, CD-ROM or smart card) into computers and devices at both ends of a data exchange before the exchange occurs unlike 'server-based keys' in which one computer generates a key and sends it to the other during the authentication session.


PTP (Peer-to-peer network)

A wireless or wired computer network that has no server or central hub or router. All the networked PCs are equally able to act as a network server or client, and each client computer can talk to all the other wireless computers without having to go through an access point or hub. However, since there is no central base station to monitor traffic or provide Internet access, the various signals can collide with each other, reducing overall performance.


Packet

See Data Packet


Passphrase

A passphrase is similar to the familiar password but is generally longer, thus offering greater security. In Wi-Fi home networking, the passphrase may be used to generate static WEP keys.


Peer-to-peer network (PTP)

See PTP and Ad-Hoc


Personal Area Network (PAN)

See PAN


Personal Digital Assistant (PDA)

See PDA


Picocell

A wireless base station of very small cell size providing, typically, less than 200m coverage. These are used mainly to provide in-building coverage and might be used with DASs.


Piconet

See PAN


Ping

A troubleshooting TCP/IP application that sends out a test message to a network device to measure the response time.


Plug and Play

A computer system feature that provides for automatic configuration of add-ons and peripheral devices such as wireless PC Cards, printers, scanners and multimedia devices.


Point-to-multipoint (PMP)

See PMP


Point-to-Point Protocol (PPP)

See PPP


Point to Point Protocol over Ethernet (PPPoE)

See PPPoE


Policy

See Security and Policy Enforcement


Port forwarding or Tunnelling

A device such as a broadband router creates a firewall between a LAN and the internet. A 'tunnel' can be created through a firewall so that computers on the Internet can communicate with one of the computers on the LAN on a single port. As Internet traffic is therefore 'forwarded' from the router port to the LAN connection port on the LAN computer, this is called port forwarding.


Port Number

This represents an endpoint or "channel" for network communications. Port numbers allow different applications on the same computer to utilise network resources without interfering with each other.

NB: The term port also refers to several other aspects of network technology. A port can refer to a physical connection point for peripheral devices such as serial, parallel, and USB ports. The term port also refers to certain Ethernet connection points, such as those on a hub, switch, or router.


Port Scan

A check performed on a computer's ports by sending a message to each port in succession, either on all or a selected number, to see which are open and the level of activity taking place. Such a scan is part of managing a network but can also be performed by a potential hacker who will look for open ports which can be probed for weaknesses.


Portal

A type of web site which acts as a doorway to multiple features and other web sites. The term originated with large, well-known Internet search engine sites that expanded their features to include email, news, stock quotes, and an array of other functionality.


Port Mirroring

Also known as a roving analysis port, this is a method of monitoring network traffic that forwards a copy of each incoming and outgoing packet from one port of a network switch to another port where the packet can be studied. A network administrator uses port mirroring as a diagnostic tool or debugging feature, especially when fending off an attack. It enables the administrator to keep close track of switch performance and alter it if necessary.


Port Monitoring

The ability to monitor the traffic passing through a port on a device to analyse network characteristics and perform troubleshooting.


Port speed

The speed that a port on a device uses to communicate with another device or the network.


Port Triggering

When data flows out on a trigger port, the router opens up the ports specified as incoming ports which act just like ports that have been forwarded while the trigger port is in use. When the trigger port stops sending data, the router waits a short time and then turns off the incoming port forwarding. Port triggering is effectively port forwarding with an on/off switch for the ports that have been forward.


Port Trunking

The ability to combine multiple ports on a device to create a single, high-bandwidth connection.


Post Office Protocol (POP)

See POP


Power over Ethernet (POE)

See POE


Pre shared key (PSK)

see PSK


Protocol

A "language" of rules and conventions for communication between network devices, a protocol includes formatting rules that specify how data is packaged into messages. It also may include conventions like message acknowledgement or data compression to support reliable and/or high-performance network communication.

Many protocols exist in computer networking ranging from the high level to the low level. The Internet Protocol family includes IP and all higher-level network protocols built on top of it, such as TCP, UDP, HTTP, and FTP.


Protocol Data Unit (PDU)

See PDU


Proxy server

See Firewall


Public Key Infrastructure (PKI)

See PKI


Public Access Location (PAL)

See Hotspot

[Danno]

Q

QoS (Quality of Service)

Quality of service is vital to ensure proper flow control and bandwidth management in a network. The capability to differentiate between time sensitive applications such as VoIP and other network data transmissions is critical. If network equipment has the ability to utilise IEEE 802.1p bits at Layer 2, DiffServ at Layer 3, and ACL lists at Layer 4, then it provides the most flexible means of delivering QoS to applications.


Quality of Service (QoS)

See QoS

[Danno]

R

RADIUS (Remote Authentication Dial-in User Service)

An Internet-standard protocol (defined in RFC 2058) that carries a remote user's authentication and configuration information between a network access server and the company's designated authentication server.


RADSL (Rate Adaptive Digital Subscriber Line)

An implementation of ADSL that automatically adjusts the connection speed to adjust for the quality of the telephone line. This feature allows RADSL service to function over longer distances than does ordinary ADSL. In RADSL, the broadband modem is configured at startup to test the phone line and adjust the data rate and typically operates at a lower date rate than standard ADSL.


RF (Radio Frequency)

A portion of the electromagnetic spectrum above the audible range and below the infra-red end of the visible light range. Generally considered to be the 30Khz to 300GHz range, these frequencies are used for all broadcast radio and television, radio communications of all kinds, microwave, mobile and satellite.


RIP (Routing Information Protocol)

The routing protocol used by the routed process on Berkeley-derived UNIX systems. Many networks use RIP as it works well for small, isolated, and topologically simple networks. RIPng (Routing Information Protocol, new generation) is the latest version.


RJ-45

Standard connectors used in Ethernet networks. Even though they look very similar to standard RJ-11 telephone connectors, RJ-45 connectors can have up to eight wires, whereas telephone connectors have only four.


RMON (Remote monitoring)

A network management protocol that is used to gather network information at a single workstation. Whereas SNMP gathers network data from a single type of MIB, RMON defines nine additional MIBs that provide a much richer set of data about network usage. For RMON to work, network devices, such as hubs and switches, must be designed to support it.


RSVP (Resource Reservation Setup Protocol)

An Internet protocol developed to enable the Internet to support specified QoS. Using RSVP, an application reserves resources along a route from source to destination. RSVP-enabled routers then schedule and prioritise packets to meet the prioritisation assigned by QoS. The purpose of RSVP is to enhance the Internet to support transmission of real-time data such as VoIP.


RTOS (Real-Time Operating System)

A component of the OSAPI module that abstracts operating systems with which other systems can interface.


Rx

Common short form used in wireless/radio to mean receive or reception of a wireless signal. See also Tx.


Radio Frequency (RF)

See RF


Range

The distance away from an AP that a wireless network can satisfactorily operate. Most Wi-Fi systems will provide a range of 30m (100ft) or more but, depending on the environment and the type of antenna used, can have a range of up to mile.


Rate Adaptive Digital Subscriber Line (RADSL)

See RADSL


Real-Time Operating System (RTOS)

See RTOS


Remote Access

Connecting a remote computing device via communications lines such as ordinary phone lines, WANs or wireless networks to access distant network applications and information, usually the home LAN. Using special software and possibly hardware, a remote computer then acts as if it is connected directly to the LAN.


Remote Authentication Dial-in User Service (RADIUS)

See RADIUS


Remote LAN Access

See Remote Access


Remote Management

The ability to control one computer from another over a network or using remote access. Suitable software must be installed on both machines which then allows control of an unattended PC from a remote location or, for example, providing instruction and technical support to remote users.


Remote monitoring (RMON)

See RMON


Repeater

With physical media like Ethernet or Wi-Fi, data transmissions can only span a limited distance before the quality of the signal degrades. Repeaters regenerate incoming electrical, wireless or optical signals thus extending the distance over which data can travel in a network.

Active hubs, also known as multiport repeaters, are repeaters but passive hubs are not. In Wi-Fi, APs function as repeaters only when operating in "repeater mode. Higher-level devices in the OSI model like switches and routers generally do not incorporate the functions of a repeater. All repeaters are technically OSI physical layer devices.


Reset

This can take two forms.

A Hard or Cold reset refers to the shutdown and restart of a device by means of hardware. This is typically done by pushing a sequence of buttons, a reset button or simply switching off and on, usually only after it has become impossible to do a soft reset. The device will go through the full boot-up sequence.

A Soft reset is similar to hitting the Ctrl+Alt+Del keys of a PC where the computer will do a limited reboot. In this case, only some of the initial start-up routines are performed, in particular missing the memory check.


Residential gateway

A wired or wireless router that includes some type of WAN capability like a Cable or DSL modem, and connects multiple PCs, peripherals on a home network thereby enabling all PCs on the network to share a single Internet connection. Most Wi-Fi residential gateways provide DHCP and NAT as well.


Resource Reservation Setup Protocol (RSVP)

See RSVP


Roaming

In networks built around multiple access points it is possible to move seamlessly from one AP coverage area to another with your laptop or desktop with no loss in connectivity.


Rogue Access Point

A term used to describe an unauthorised access point that is connected on the main home or corporate network or operating in a stand-alone mode (in a car park or in a neighbour's building). Rogue APs, by definition, are not under the management of network administrators and do not conform to network security policies and may present a severe security risk. Ideally, it is best to have some type of WLAN system that does not allow rogue access points to easily be added to an existing WLAN.


Router

A physical device that joins multiple wired or wireless networks together and forwards data packets from one local area network (LAN) or wide area network (WAN) to another. Based on routing tables and routing protocols, routers can read the network address in each transmitted frame and make a decision on how to send it via the most efficient route based on traffic load, line costs, speed, bad connections, etc. For example, an IP router such as a DSL modem broadband router joins the home's LAN to the WAN of the Internet.


Routing (Layer 3 Switching)

Routers utilise information in the header of an IP packet in order to "route" traffic toward their destination. Routers and Layer 3 Switches learn where to direct traffic by participating in protocols such as RIP or OSPF. Traditionally routers have been high-latency software-based devices that struggled to keep up with increasing traffic loads and classification requirements. With the advent of high speed silicon-based switching, both Layer 2 and now Layer 3 forwarding decisions occur in hardware at wire speed. The elimination of the Layer 3 "penalty" enables the "routing" of traffic at speeds traditionally only available to Layer 2 switching.


Routing Information Protocol (RIP)

See RIP

[Danno]

S

SA (Security Association)

A group of security settings related to a specific VPN tunnel. A SA groups together all the necessary settings needed to create a VPN tunnel. Different SAs may be created to connect branch offices, allow secure remote management, and pass unsupported traffic. All SAs require a specified encryption method, IPSec gateway address and destination network address.


SAN (Storage Area Network)

A high performance LAN designed for server clusters. A typical application of a SAN is network data storage supporting transfers of large quantities of data to and from multiple disk arrays.


SDSL (Symmetric Digital Subscriber Line)

A form of DSL service that provides equal bandwidth for both uploads and downloads. Originally developed in Europe, SDSL was one of the earliest forms of DSL to not require multiple telephone lines. SDSL supports data rates up to 3,088 Kbps.


SFP (Small Form-Factor Pluggable)

Denotes a smaller size GBIC module that takes up about half the size of the original GBIC module. Also known as mini GBIC.


SHA (Secure Hash Algorithm)

A set of related cryptographic hash functions of which the most commonly used is SHA-1 in popular security applications and protocols such as TLS, SSL and IPSec. The SHA algorithms were designed by the US National Security Agency and published as a US government standard.


SIP (Session Initiation Protocol)

An IETF standard protocol for initiating an interactive user session that involves multimedia elements such as video, voice, chat, gaming and virtual reality.

SIP is a request-response protocol, dealing with requests from clients and responses from servers. Participants are identified by SIP URLs. Requests can be sent through any transport protocol, such as UDP, SCTP, or TCP. SIP determines the end system to be used for the session, the communication media and media parameters, and the called party's desire to engage in the communication. Once these are assured, SIP establishes call parameters at either end of the communication, and handles call transfer and termination.

The Session Initiation Protocol is specified in IETF RFC 2543.


SMII (Serial Media Independent Interface)

A standard that reduces the number of pins needed to connect Fast Ethernet Switch chips to physical layer transceivers.


SMTP (Simple Mail Transfer Protocol)

The application layer protocol in TCP/IP which deals with the transmission of email over the Internet.


SNMP (Simple Network Management Protocol) & Web-based Management

An IETF standard protocol for managing devices on a TCP/IP network. It allows a Network Management System such as HP OpenView to configure, monitor and gather information about network devices and critical interfaces. By interacting with the MIB on a device, a network manager can monitor connectivity, configure parameters and gather critical interface statistics for troubleshooting and capacity planning. This same information is available via a Web-based interface to enable Web browser access from anywhere in the network.


SPI (Stateful Packet Inspection) Firewall

A firewall providing the highest form of protection for routers. A SPI firewall automatically provides rigorous inspections of all inbound and outbound communications, protecting a network against malicious attacks that flood it with inappropriate packets/data.


SSH (Secure Shell)

Sometimes known as Secure Socket Shell, this is a Unix-based command interface and protocol which provides secure access between a remote computer and server and in which all interactions are encrypted.


SSID (Service Set Identifier)

See ESSID


SSL (Secure Sockets Layer)

Commonly used encryption scheme used by many online retail and banking sites to protect the financial integrity of transactions. When an SSL session begins, the server sends its public key to the browser which then sends a randomly generated secret key back to the server in order to have a secret key exchange for that session.


STP (Spanning Tree Protocol)

A protocol that finds the most efficient path between segments of a multi-looped, bridged network. STP allows redundant switches and bridges to be used for network resilience, without the broadcast storms associated with looping. If a switch or bridge fails, a new path to a redundant switch or bridge is opened.


Satellite broadband

A wireless high-speed Internet connection provided by satellites. Some satellite broadband connections are two-way- up and down. Others are one-way, with the satellite providing a high-speed downlink and then using a dialup telephone connection or other land-based system for the uplink to the Internet.


Schedule

A feature present in some Netgear products where it is possible to limit access to certain users/machines/services on the LAN according to the time and/or day of week.


Secure Hash Algorithm (SHA)

See SHA


Secure Shell (SSH)

See SSH


Secure Sockets Layer (SSL)

See SSL


Secure Hyper Text Transport Protocol or HTTP over SSL (HTTPS)

See HTTPS


Security Association (SA)

See SA


Security and Policy Enforcement

Network security and policy enforcement is crucial to the reliable operation of any mission-critical infrastructure. The overall goal of policy-based networking is to enable the implementation, control and modification of policies across a network without having to access each device in your network. At their simplest level, policies define the ability to allow or deny access to network resources. The first line of control is at the port level. IEEE 802.1x port-based authentication can be used with a RADIUS server to maintain a universal login and secure the physical network port. Once authenticated for port access, ACLs can enforce additional policies on a per port, per MAC or per IP address basis, all at wire speed. ACLs can ensure that once a user is on the network, he can only access those resources for which he has authorisation. IEEE 802.1x and ACLs ensure that only authorised users have access to specific resources and block off any unwarranted attempts to reach network resources.


Segment

A specially-configured subset of a larger network. The boundaries of a network segment are established by devices capable of regulating the flow of packets into and out of the segment, including routers, switches, hubs and bridges.

Network designers create segments to physically separate related computers into groups. This grouping can improve network performance and security. In Ethernet networks, for example, computers send many broadcast packets onto the network, but only other computers on the same segment receive them. Network segments and subnets serve similar purposes; both create a grouping of computers. The difference between a segment and a subnet is as follows: a segment is a physical network construction, whereas a subnet is simply a higher-level software configuration. In particular, a single IP subnet that functions correctly across multiple segments cannot be defined.


Server

A computer that provides its resources to other computers and devices on a network. These include print servers, Internet servers and data servers. A server can also be combined with a hub or router.


Server NTP

In a computer network, one computer is designated as the primary time server and all other computers use this machine as the time reference. On a regular basis each client computer will initiate a time request exchange with the time server from which the client is able to calculate the link delay, its local offset, and adjust its local clock to match the clock at the server's computer.


Session Initiation Protocol (SIP)

See SIP


Short Set Identifier (SSID), (also called ESSID)

See ESSID


SimpleX signaling (SX)

SX is one of IEEE 802.3's designations for media. For example, 1000SX indicates 1000 gigabit Ethernet over "short haul" or "short wavelength" optical fibre.


Site survey

A physical environment survey to determine the placement of APs and antennas for a wireless network, as well as the number of devices necessary to provide optimal coverage, in a new or expanding installation. A piece of equipment, called a spectrum analyser, is typically used to identify areas of interference to avoid in AP placement.

The term might also refer to a survey for a wired network, to determine the placement of cables and equipment.


Serial Media Independent Interface (SMII)

See SMII


Small Form-Factor Pluggable (SFP)

See SFP


Smart Switch

A NETGEAR to indicate a family of Switches which fill the gap between unmanaged and fully managed switches, providing network control without the cost and complexity of a full Layer 2/Layer 3 management implementation. Managed through a web browser, Smart Switches offer Link Aggregation, VLAN, and QoS capabilities through an intuitive user interface.


Simple Mail Transfer Protocol (SMTP)

See SMTP


Simple Network Management Protocol (SNMP) & Web-based Management

See SNMP


Spam

The term refers to unsolicited commercial advertisements distributed online. Most spam comes to people via email, but spam can also be found in online chat rooms and message boards.


Spanning Tree

A technique that detects loops in a network and logically blocks the redundant paths, ensuring that only one route exists between any two LANs.


Spanning Tree Protocol (STP)

See STP


Stateful Packet Inspection (SPI) Firewall

See SPI


Static IP and Dynamic IP Addressing

See Dynamic IP and Static IP Addressing


Static Routing

The process in which a system network administrator would manually configure network routers with all the information necessary for successful packet forwarding by constructing the routing table in every router in a network path. Static routes to network destinations are unchangeable, except by the administrator, unlike in dynamic routing.


Subnetwork or Subnet

Network designers employ subnets as a way to partition networks into logical segments for greater ease of administration. Found in larger networks, these smaller networks are used to simplify addressing between numerous computers. Subnets connect to the central network through a router, hub or gateway. Each individual wireless LAN will probably use the same subnet for all the local computers it talks to.


Subnet Mask

Combined with the IP address, the IP Subnet Mask allows a device to know which other addresses are local to it, and which must be reached through a gateway or router.


SuperG

An industry label applied to wireless devices based on the 802.11g standard but which use non-standard, proprietary technologies that aren't part of the official 802.11g standard to achieve 108Mbps performance.


Switch

A type of hub that efficiently controls the way multiple devices use the same network so that each can operate at optimal performance. It transmits packets to only the receiving port rather than to all ports as a hub does. Also see Smart Switch.


Symmetric Digital Subscriber Line (SDSL)

See SDSL


Symmetric Network

See Asymmetric

[Danno]

T

TCP (Transmission Control Protocol)

A protocol used along with the IP to send data in the form of individual packets between computers over the Internet. While IP takes care of handling the actual delivery of the data, TCP takes care of keeping track of the packets that a message is divided into for efficient routing through the Internet. For example, when a web page is downloaded from a web server, the TCP program layer in that server divides the file into packets, numbers the packets, and then forwards them individually to the IP program layer. Although each packet has the same destination IP address, it may get routed differently through the network. At the other end, TCP reassembles the individual packets and waits until they have all arrived to forward them as a single file.


TCP/IP (Transmission Control Protocol/Internet Protocol)

The underlying technology behind the Internet and communications between computers in a network. The first part, TCP, is the transport part, which matches the size of the messages on either end and guarantees that the correct message has been received. The IP part is the user's computer address on a network. Every computer in a TCP/IP network has its own IP address that is either dynamically assigned at start-up or permanently assigned. All TCP/IP messages contain the address of the destination network as well as the address of the destination station. This enables TCP/IP messages to be transmitted to multiple networks (subnets) within an organisation or worldwide.

IP corresponds to the Network layer (Layer 3) in the OSI model, whereas TCP corresponds to the Transport layer (Layer 4) in OSI. In other words, the term TCP/IP refers to network communications where the TCP transport is used to deliver data across IP networks.


TFTP (Trivial File Transfer Protocol)

A simple form of the FTP, TFTP uses the UDP and provides no security features. It is often used by servers to boot diskless workstations, X-terminals, and routers.


TKIP (Temporal Key Integrity Protocol)

A security feature that is a WEP enhancement providing important data encryption enhancements including a per-packet key mixing function, a message integrity check (MIC) named Michael, an extended initialisation vector (IV) with sequencing rules, and a re-keying mechanism.


TLS (Transport Layer Security)

TLS is a protocol that guarantees privacy and data integrity between client/server applications communicating over the Internet. The TLS protocol is made up of two layers. The TLS Record Protocol ensures that a connection is private by using symmetric data encryption and ensures that the connection is reliable. The second TLS layer is the TLS Handshake Protocol, which allows authentication between the server and client and the negotiation of an encryption algorithm and cryptographic keys before data is transmitted or received. TLS supersedes and is an extension of SSL. TLS and SSL are not interoperable.


TTLS (Tunnelled Transport Layer Security)

A wireless security protocol that combines network-based certificates with other authentication such as tokens or passwords. Also known as EAPTTLS, TTLS offers strong mutual authentication without having to distribute and manage certificates.


Tx

Common short form used in wireless/radio to mean transmit or transmission of a wireless signal. See also Rx.


Telecommuter/Mobile User

A computer user e.g. a home worker, who connects to a corporate LAN using remote access technologies, for example, broadband or VPN.


Telephony

The term refers to voice communication using telephone networks. Originally this meant analogue electrical signalling over copper wire. This form is still in widespread use but other forms, such as radio and mobile telephony plus VoIP, now exist.


Telnet

A terminal emulation program for TCP/IP networks such as the Internet, it allows a server to be controlled by a remote computer. It is commonly used to remotely control Web servers.


Temporal Key Integrity Protocol (TKIP)

See TKIP


Thick Ethernet

A type of Ethernet cable, Thick Ethernet, or thicknet, is 0.4" diameter coaxial cable. This allows transmission over greater distances than Thin Ethernet which is only 0.2" diameter.


Thin Ethernet

See Thick Ethernet


Traffic Meter

A piece of software which can analyse a stream of packets passing across an IP network between two end points or being sent from a single end point. It can provide useful data to network operators about how the network is being used.


Traffic prioritisation

Giving time-critical data traffic a higher quality of service over other, non-critical data traffic.


Transmission Control Protocol (TCP)

See TCP


Transport Layer Security (TLS)

See TLS


Transmission Control Protocol/Internet Protocol (TCP/IP)

See TCP/IP


Trivial File Transfer Protocol (TFTP)

See TFTP


Trunking

See Link Aggregation


Tunnelled Transport Layer Security (TTLS)

See TTLS


Tunnelling

See Port forwarding or Tunnelling

[Danno]

U

UDP (User Datagram Protocol)

A direct protocol used to communicate datagrams over a network with little error recovery.


UMA (Unlicensed Mobile Access)

A technology which can provide access to GSM and GPRS mobile services over unlicensed spectrum technologies like Bluetooth and 802.11 making it possible for subscribers to roam and handover seamlessly between private unlicensed wireless networks, GSM networks, LANs, and the public switched telephone network (PSTN) using the same multi-mode mobile phone.

It lets mobile operators deliver voice, data and IMS/SIP applications to mobile phones on Wi-Fi access networks.


UPnP (Universal Plug and Play)

A set of computer network protocols, promulgated by the UPnP Forum, offering simple network connectivity of PCs, intelligent appliances, and wireless devices. It defines a set of common interfaces that describe devices and services, allow automatic discovery when a device is plugged into a network, and allow other devices and people to use them without complicated setup or configuration.


URI (Uniform Resource Identifier)

A standard global identifier for an Internet resource that may be local or remotely accessible. URIs follow the same general syntax as URLs, a URL being one type of URI. Whereas URLs always refer to network addresses (including a protocol specification, host name or address, and local path), a URI does not necessarily refer to a remote resource. For example, the URI file:///c:/ specifies a local directory but because the file does not refer to any specific network protocol, this URI is not also a URL.


URL (Uniform Resource Locator)

A specially-formatted text string that defines a location on the Internet. URL strings contain three parts or substrings:

* network protocol
* host name or address
* file location

The network protocol substring determines the underlying Internet protocol to be used in reaching the location. These strings consist of a standard protocol name followed by the :// characters. Typical protocols found in URLs include http://, ftp://, and mailto:.

The host substring immediately follows the protocol definition. Hosts may be defined by Internet-standard naming (DNS) or by IP address. For example, a URL http://compnetworking.about.com or, equivalently, http://209.143.212.20 contains the protocol and host information needed to access this Web site.


USB (Universal Serial Bus)

A high-performance networking standard based on serial bus architecture. Most new computers and associated peripheral devices like printers and scanners support USB. USB hubs for file and printer sharing also exist. One USB network supports up to 127 devices.

The first commercial incarnations of USB - USB 1.0 and USB 1.1 - supported a maximum data rate of 12 Mbps. The current version - USB 2.0 - supports a much faster rate of 480 Mbps


UTP cable (Unshielded Twisted Pair cable)

Two paired wires with wire twisted two or more times per inch to help cancel out noise.


Unicast

A packet sent to a single endstation on a network.


Uniform Resource Identifier (URI)

See URI


Uniform Resource Locator (URL)

See URL


Universal Plug and Play (UPnP)

See UPnP


Universal Serial Bus (USB)

See USB


Unlicensed Mobile Access (UMA)

See UMA


Unshielded Twisted Pair cable (UTP cable)

See UTP Cable


Upload

See Download


Upstream

See Downstream


User Datagram Protocol (UDP)

See UDP

[Danno]

V

VDSL (Very high speed Digital Subscriber Line)

A form of DSL that supports very high-bandwidth applications such as High-Definition Television (HDTV). VDSL is not as widely deployed as other forms of DSL service. However, VDSL can achieve data rates up to approximately 51,840 Kbps, making it the fastest available form of DSL. To perform at this speed, VDSL relies on fibre optic cabling. VDSL is designed to work more as a business service that uses ATM internetworking rather than as a consumer service that utilises IP.


VLAN (Virtual LAN)

A logical association that allows users to communicate as if they were physically connected to a single LAN, independent of the actual physical configuration of the network. By using this Layer 2 technology, traffic within a VLAN will only go to members of that VLAN. This is useful for limiting broadcast traffic as well as providing a level of security. Network administrators can improve bandwidth and improve security by segmenting users into different logical groups, e.g. Finance VLAN vs. Sales VLAN. A router or Layer 3 switch must forward traffic destined for another VLAN.


VoIP (Voice over IP or Voice over Internet Protocol)

VoIP converts analogue voice signals into digital data packets and supports real-time, two-way transmission of conversations using IP - IP telephony. Telephone calls can be made on the Internet using a VoIP service provider and standard computer audio systems. Alternatively, some service providers support VoIP through ordinary telephones that use special adapters to connect to a home computer network. VoIP can offer a substantial cost savings over traditional long distance telephone calls. The main disadvantage of VoIP is, like mobile phones, a greater potential for dropped calls and generally lesser voice quality but this disadvantage is being reduced very quickly.


VPN (Virtual Private Network)

A private network of computers that's at least partially connected by public phone lines. With a VPN, remote users typically connect to an Internet service provider (ISP) or a private IP-based network and from there establish a secure connection with network servers via an encrypted tunnel.

VPNs use encryption and other security mechanisms to ensure that only authorised users can access the network and that the data cannot be intercepted. VPNs can also be used for secure communication across a LAN or WAN.


VPN End Point

VPN end point capability within a router provides the ability to initiate a VPN tunnel to some other location that supports either a VPN client (client-to-box) or has VPN end point capability (box-to-box).


VRRP (Virtual Router Redundancy Protocol)

Designed to eliminate a single point of failure, VRRP dynamically assigns routing responsibility to one of multiple routers on a LAN (the Master router). VRRP provides dynamic fail-over via a secondary router should the Master router become unavailable. The advantage gained from using VRRP is a higher availability default gateway without requiring configuration of dynamic routing or router discovery protocols on every end user device.


Very high speed Digital Subscriber Line (VDSL)

See VDSL


Virtual LAN (VLAN)

See VLAN


Virtual Private Network (VPN)

See VPN


Virtual Router Redundancy Protocol (VRRP)

See VRRP


Voice over IP or Voice over Internet Protocol (VoIP)

See VoIP

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W

WAN (Wide Area Network)

A computer network that spans a relatively large geographical area. Typically, a WAN consists of two or more LANs. WANs generally utilise different and much more expensive networking equipment than do LANs. Key technologies often found in WANs include SDH, Frame Relay, and ATM. The world's most popular WAN is the Internet of which some segments, like VPN-based extranets, are also WANs in themselves.


WAP (Wireless Application Protocol)

A network architecture for content delivery over wireless networks. Central to the design of WAP is a network stack based on the OSI model. WAP implements several new networking protocols that perform functions similar to the well-known Web protocols HTTP, TCP, and SSL. WAP includes the concepts of browsers, servers, URLs, and gateways. WAP browsers are intended to be implemented on small mobile devices such as mobile phones, pagers, and PDAs.


WAP (Wireless Access Points)

Specially configured nodes on WLANs which act as a central transmitter and receiver of WLAN radio signals. WAPs used in the home or small business networks are generally small, dedicated hardware devices featuring a built-in network adapter, antenna, and radio transmitter.


WDS (Wireless Distribution System)

Also called Wireless LAN Bridging, a system that enables the interconnection of access points wirelessly, specifically two or more 802.11 access points that send traffic between them as opposed to between access point and a client computer. WDS pre-configures each packet forwarding path and the paths are static. All base stations in a WDS must be configured to use the same radio channel, and share WEP keys if that is used.


WEP (Wired Equivalent Privacy)

WEP is a protocol that adds security to WLANs based on the 802.11 Wi-Fi standard. It is an OSI Data Link layer (Layer 2) security technology that can be turned "on" or "off." WEP was designed to give wireless networks the equivalent level of privacy protection as a comparable wired network and is available in 108-bit (also called 128-bit), or in 152-bit encryption modes. As 152-bit encryption provides a longer algorithm that takes longer to decode, it can provide better security than basic 40-bit (64-bit) encryption. Regardless of how it is implemented on a WLAN, WEP represents just one element of an overall WLAN security strategy.


WFA (Wi-Fi Alliance)

Formerly WECA (Wireless Ethernet Compatibility Alliance), the Wi-Fi Alliance is a non-profit international association formed in 1999 to certify interoperability of wireless Local Area Network products based on IEEE 802.11 specification. The goal of the Wi-Fi Alliance's members is to enhance the user experience through product interoperability. For more details go to http://www.weca.net or http://www.wi-fi.org.


Winipcfg

A Microsoft WIN98 utility program that allows a user to find a computer's network addresses and other useful TCP/IP settings. It may also fix network connection problems in certain situations.


WINS (Windows Internet Naming Service)

A server process for resolving Windows-based computer names to IP addresses. If a remote network contains a WINS server, a Windows PCs can gather information from that WINS server about its local hosts. This allows a PC to browse that remote network using the Windows Network Neighbourhood feature.


WISP (Wireless Internet Service Provider)

An ISP providing services over public wireless networks. WISPs typically install Wi-Fi hotspots in airports, hotels and other public business places. These hotspots provide Internet access and LAN printing for mobile network devices like laptops, handheld computer and cell phones. Other WISPs offer services over WiMax networks.


WLAN (Wireless LAN)

A type of LAN that uses radio or infrared signals rather than wires to communicate between nodes. Currently a WLAN typically extends an existing wired local area network. WLANs are built by attaching a device called the access point (AP) to the edge of the wired network. Clients communicate with the AP using a wireless network adapter similar in function to a traditional Ethernet adapter.


WMAN (Wireless Metropolitan Area Networks)

Networks designed to the 802.16 standard, otherwise known as Wi-Max, for typical ranges of up to 30 miles or 50km.


WMM™ (Wi-Fi Multimedia)

A new technology offering the packet prioritisation component from the 802.11e QoS standard, allowing packets which contain time-dependent data, such as audio or video, to be sent ahead of data that can wait a few microseconds. This kind of technology is important for home entertainment networks set up to distribute multiple TV, video, and audio streams around the house.


WPA (Wi-Fi Protected Access)

A security technology for wireless networks that improves on WEP. One of the key technologies behind WPA is the TKIP which addresses the encryption weaknesses of WEP. WPA has built-in authentication which provides roughly comparable security to VPN tunnelling with WEP, with the benefit of easier administration and use. This is similar to 802.1x support and requires a RADIUS server in order to implement.

One variation of WPA is called WPA-PSK (Pre Shared Key). It is a simplified (no RADIUS server required) but still powerful form of WPA most suitable for home Wi-Fi networking. To use WPA-PSK, a person sets a static key or "passphrase" as with WEP but WPA-PSK automatically changes the keys at a preset time interval, making it much more difficult for hackers to find and exploit them.


WPA2

An update of WPA in line with the IEEE 802.11i security specification. It replaces WPA and has been available since June 2004.


WPAN (Wireless Personal Area Network)

Networks designed to the 802.15 standard for typical ranges of 10m.


WWW (World Wide Web)

The open development phase of the Internet that occurred in the 1990s and continues today. The WWW consists of all the global public Web sites hosted on server computers and the client devices (computers, mobile phones, etc.) that access their Web content.

Technically, the WWW is constructed using the following set of technologies:

* HTML - Hypertext Markup Language
* HTTP - Hypertext Transfer Protocol
* Web servers and Web browsers

Researcher Tim Berners-Lee led the development of the original WWW in 1992. He built prototypes of all the above technologies and coined the term WWW. He is now Director of the World Wide Web Consortium (W3C) which administers and sets the standards for the WWW.


War Chalking

The act of making chalk marks on outdoor surfaces (walls, pavements, buildings, sign posts, trees) to indicate the existence of an open wireless network connection, usually offering an Internet connection so that others can benefit from the free wireless access. The open connections typically come from the access points of wireless networks located within buildings to serve enterprises. The chalk symbols indicate the type of access point that is available at that specific spot.


War Driving

The act of locating and possibly exploiting connections to wireless local area networks while driving around a city or elsewhere. Because a wireless LAN may have a range that extends beyond an office building, an outside user may be able to intrude into the network due to lack of WLAN security, obtain a free Internet connection, and possibly gain access to company records and other resources.


Web (World-Wide Web, WWW or W3)

An Internet client-server system to distribute information, based upon the hypertext transfer protocol (HTTP).


Wide Area Network (WAN)

See WAN


Wi-Fi

The industry name for wireless LAN (WLAN) communication technology related to the IEEE 802.11 family of wireless networking standards. The Wi-Fi Alliance certifies vendor products to ensure 802.11 products on the market follow the various 802.11 specifications.


Wi-Fi Alliance (WFA)

See WFA


Wi-Fi Multimedia (WMM™)

See WMM™


Wi-Fi Protected Access (WPA)

See WPA


WiMax (Worldwide Interoperability for Microwave Access)

IEEE 802.16 is the specification for long range fixed broadband wireless access systems employing a PMP architecture in the frequency range 10-66 GHz. The standard covers both the MAC and the PHY layers. WiMax is the industry term for this technology which can deliver high-speed Internet access to rural areas and other locations not serviced by cable or DSL technology.


WiMax Forum

WiMax is developed by an industry consortium, overseen by a group called the WiMax Forum. The WiMax Forum certifies WiMax equipment to ensure it meets the technology standards.


Windows Internet Naming Service (WINS)

See WINS


Wired Equivalent Privacy (WEP)

See WEP


Wireless Application Protocol (WAP)

See WAP


Wireless Access Point (WAP)

See WAP


Wireless AP Support

An AP functioning as a bridge to connect two Ethernet LANs.


Wireless Client Security Separator

A security setting built into some wireless networks that disables the ability of wireless clients to communicate directly.


Wireless Distribution System (WDS)

See WDS


Wireless Internet Service Provider (WISP)

See WISP


Wireless LAN (WLAN)

See WLAN


Wireless Metropolitan Area Networks (WMAN)

See WMAN


Wireless networks

An alternative to wired networking that relies on copper and/or fibre optic cabling between network devices, wireless networks use radio to maintain communication channels between computers and other devices. Advantages of wireless include mobility and elimination of unsightly cables. Disadvantages of wireless include the potential for radio interference due to weather, other wireless devices, or obstructions like walls. WLAN products generally conform to the 802.11 "Wi-Fi" standards whereas WiMax networks conform to 802.16.


Wireless Peer to Peer Isolation

A feature present in some wireless networks which prevents wireless network users from being able to communicate with each other via the wireless network. This is a security feature that is especially useful in public wireless hotspot applications.


Wireless Personal Area Network (WPAN)

See WPAN


Wireless Routers

Wireless routers are three devices in one box:

* LAN controller - so the PC doesn't need to be on
* WAP - allowing wireless connection of devices to the router
* 4-port Switch - allowing connection of wired Ethernet devices.

Wireless routers offer flexibility, allowing connection of both wired and wireless devices plus sharing of a broadband connection.


Wire Speed Performance

Wire speed performance is the ability to perform all required packet processing and forward the traffic at the fastest rate that packets are allowed to travel on the wire, defined by the IEEE standard. With all forwarding decisions occurring in Application Specific Integrated Circuits (ASICs), wire speed switching and routing performance is assured. Concentration of services in hardware delivers performance at an extremely economic price. When combined with a non-blocking architecture that ensures zero packet loss, the traditional bandwidth and latency bottlenecks are easily reduced or eliminated.


Wizard

An interactive computer program which acts as an interface to lead a user through a complex task, or set of tasks, using simple steps.


World Wide Web (WWW)

See WWW

[Danno]

X

xDSL

Refers to the complete family of related DSL technologies, ADSL, SDSL, VDSL etc. rather than any one specific implementation.


XR (Extended Range)

A feature of some wireless networking hardware which extends the wireless network range.

[Danno]

Y

[Danno]

Z