Glossary E

Glossary Index

E - H

Encapsulation	Encapsulating data is a technique used by layered protocols in which a low level protocol accepts a message from a higher level protocol, then places it in the data portion of the lower-level frame. The logistics of encapsulation require that packets traveling over physical network contain a sequence of headers. The first header derives from the physical network frame, the second from the IP frame, the third from the physical network frame, and so on. Encapsulation enables the transmission of data over different network portions based on differing protocols.
Ethernet	Ethernet is a physical and data link layer technology for local area networks (LANs). Ethernet was invented by engineer Robert Metcalfe. Higher level network protocols like Internet Protocol (IP) use Ethernet as their transmission medium. Data travels over Ethernet inside protocol units called frames.
Extranet	An extranet is 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.
Fast Ethernet	Fast Ethernet supports a maximum data rate of 100 Mbps. It is so named because original Ethernet technology supported only 10 Mbps.
Filter	A set of rules that define what packets may pass through a network. Filters can use destinations, sources or protocols to determine what to do with packets. One of the packet's headers must contain information that matches the information in the rules or the packet filter will discard it. See also Firewall, Secure Access Firewall, Secure Access Manager.
Firewall	A network firewall protects a computer network from unauthorized access. Network firewalls may be hardware devices, software programs, or a combination of the two. Many home network router products include built-in firewall support. The administrative interface of these routers includes configuration options for the firewall. Router firewalls can be turned off (disabled), or they can be set to filter certain types of network traffic through so-called firewall rules. Another common form of network firewall is a proxy server. Proxy servers act as an intermediary between internal computers and external networks 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.
FireWire	FireWire is a high performance networking standard based on serial bus architecture similar to USB. FireWire is also known as the IEEE 1394 standard, created in 1995.
Frame Relay	Frame relay is a data link network protocol designed to transfer data on Wide Area Networks (WANs). Frame relay works over fiber optic or ISDN lines. The protocol offers low latency and to reduce overhead, does perform any error correction, which is instead handled by other components of the network. Frame relay has traditionally provided a cost-effective way for telecommunications companies to transmit data over long distances. Frame relay has decreased in popularity as companies are gradually migrating their deployments to Internet Protocol (IP) based solutions.
Framing	At the physical and data link layers of the OSI model, bits are fit into units called frames. Frames contain source and destination information, flags to designate the start and end of the frame, plus information about the integrity of the frame. All other information, such as network protocols, and the actual payload of data, is encapsulated in a packet, which is encapsulated in the frame.
File Transfer Protocol (FTP)	FTP allows you to transfer files between two computers on the Internet. FTP is a simple network protocol based on Internet Protocol and also a term used when referring to the process of copying files when using FTP technology. To transfer files with FTP, you use a program often called the "client." The FTP client program initiates a connection to a remote computer running FTP "server" software. 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 requires a username and password as set by the administrator of the server. Many public FTP archives follow a special convention for that accepts a username of "anonymous.". FTP supports two modes of data transfer: plain text (ASCII), and binary.
Gateway	A network gateway is an internetworking system capable of joining together two networks that use different base protocols. A network gateway can be implemented completely in software, completely in hardware, or as a combination of both. Depending on the types of protocols they support, network gateways can operate at any level of the OSI model. Because a network gateway, by definition, appears at the edge of a network, related capabilities like firewalls tend to be integrated with it. On home networks, a broadband router typically serves as the network gateway although ordinary computers can also be configured to perform equivalent functions.
H.323	H.323 is a protocol standard for multimedia communications. H.323 was designed to support real-time transfer of audio and video data over packet networks like IP. The standard involves several different protocols covering specific aspects of Internet telephony. The International Telecommunication Union (ITU-T) maintains H.323 and these related standards. Most voice over IP (VoIP) applications utilize H.323. H.323 supports call setup, teardown and forwarding/transfer. Architectural elements of a H.323 based system are Terminals, Multipoint Control Units (MCUs), Gateways, an optional Gatekeeper and Border Elements. Different functions of H.323 run over either TCP or UDP. Overall, H.323 competes with the newer Session Initialization Protocol (SIP), another proven standard often found in VoIP systems. A key feature of H.323 is Quality of Service (QoS). QoS technology allows real-time prioritization and traffic management constraints to be placed on "best-effort" packet delivery systems like TCP/IP over Ethernet. QoS improves the quality of voice or video feeds.
HDSL	HDSL technology was developed in the early 1990s, making it one of the oldest forms of DSL. HDSL service provides equal bandwidth for both downloads and uploads, offering data rates up to 2,048 Kbps. Note that HDSL requires multiple phone lines to accomplish this. Like other forms of DSL, HDSL features "always on" combined voice and data services. HDSL enjoyed some popularity in years past, but the technology has effectively been replaced by alternatives like SDSL that only require one phone line and offer similar performance and reach.
HDLC (High-level Data Link Control)	A synchronous, bit-oriented Link Layer protocol for data transmission. Frame Relay is an example of an HDLC-based packet protocol.
Hop	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.
HSDPA (High Speed Downlink Packet Access)	HSDPA is a protocol for data communications on cellular networks. HSDPA supports theoretical data rates of 1.8 Mbps and up to 14.4 Mbps maximum, although typical speeds are closer to 500 Kbps.
HTTP (Hypertext Transfer Protocol)	HTTP - the Hypertext Transfer Protocol - provides a standard for Web browsers and servers to communicate. The definition of HTTP is a technical specification of a network protocol that software must implement. HTTP is an application layer network protocol built on top of TCP. HTTP clients (such as Web browsers) and servers communicate via HTTP request and response messages. The three main HTTP message types are GET, POST, and HEAD. HTTP utilizes TCP port 80 by default, though other ports such as 8080 can alternatively be used.