G

GNU Privacy Guard (GNUpg)
GNUpg (G [has no meaning] Not UNIX) is an encryption system that should replace PGP. Unlike PGP, GNUpg is copyright free and was created in Germany; U.S. citizens cannot be charged with treason for exporting it. Refer to http://www.gnu.org for additional information.

Gateway
A gateway is a protocol converter. This type of gateway converts data between two distinct types of protocol architectures, often at the higher layers of the OSI model. 2. A gateway is a router used to connect a private network to a public network, typically the Internet.

Graphics Interchange Format (GIF)
GIF is one of two graphic image formats used in HTML (JPEG is the other type). GIF files, the more popular format for small or simple images, are limited to 256 colors, have a lower resolution, offer lossless compression, and can be made transparent for a popular type of borderless effect.

GroupWise
GroupWise is an e-mail application package produced by Novell that runs in conjunction with Novell NetWare.

H

Hack
An unorthodox, often clever, solution to a problem is referred to as a hack. The line that divides hacks from kludges can sometimes be very fine. See kludge.

Hardware
Hardware is the physical part of a computer which can include hard drives, circuit boards inside a computer, and other computer components.

Hardware Address
A hardware address is the address hard-coded into the NIC of the destination node. This address is the same as a MAC or NIC address.

Header
A header is part of a message, packet, or frame that contains information necessary to send a unit of information from one node to another. The header normally contains a field specifying the length of the encapsulated message, together with at least one field providing information about the message. If, for example, the message is a segment of a larger message, the header might specify the relative position of the segment in the complete message, and probably the total number of segments in the message.

High-Level Data Link Control (HDLC)
The HDLC protocol suite represents a wide variety of link layer protocols such as SDLC, LAPB, and LAPD.

Hop Count
The number of intermediate routers a packet must traverse to travel from source to destination in a multirouter environment is referred to as a hop count.

Host
A host is any computer system attached to a TCP/IP network. An IP host may be a personal computer, port on a terminal server, UNIX workstation, router, or supercomputer.

Hypermedia
Hypermedia takes hypertext to another level, and includes images, sounds, and video with links that can be selected and viewed.

Hypertext
Hypertext is computer information containing text that can be linked with selected phrases. The links point to other documents or files. Hypertext is basically the same as regular text, however, it contains connections within the text to other documents. The links in the text are called hyperlinks.

Hypertext Markup Language (HTML)
HTML is the language the Web uses for creating and recognizing hypermedia documents. HTML is known for its ease of use. HTML documents are 7-bit ASCII files, with formatting codes that contain information about layout (text styles, document title, paragraphs, and lists) and hyperlinks.

Hypertext Transfer Protocol (HTTP)
HTTP is an application-level protocol used to send information between computers attached to the Web.

Hub
Also called a wiring concentrator, a simple hub is a repeater with multiple ports. A signal coming into one port is repeated out the other ports.

I

In-Band Management
In-band management is the process of controlling a network device by sending network management commands over the network itself.

Index of Refraction
The ratio of the velocity of light in a vacuum to the velocity of light in a medium such as optical fiber is referred to as the index of refraction. See refraction.

Input/Output (I/O)
An I/O channel is the path from the main processor, or CPU, of a computer to its peripheral devices.

Institute of Electrical and Electronic Engineers (IEEE)
IEEE publishes communications standards such as the 802 series that define shared-medium networks.

Interexchange Carrier (IEC)
IEC (also IXC) is a service provider that carries user transmission across long distances (e.g., AT&T, MCI, and Sprint).

Integrated Services Digital Network (ISDN)
ISDN can be characterized as a bundle of services offered for the transmission of voice, data, and other forms of communication via the switched telephone network.

Interim Local Management Interface (ILMI)
ILMI is an interim specification for network management functions that is based on a limited subset of SNMP capabilities. The ATM Forum defined ILMI for network management between an end user and public or private network, and between a public network and private network.

Interleaf Ratio
An interleaf ration is a value used in class-of-service routing that specifies the number of high-priority packets to be transmitted for each low-priority packet. For example, if the interleaf ratio is set to five, a router transmits five high-priority packets for each one low-priority packet.

International Data Encryption Algorithm (IDEA)
IDEA is a block encryption algorithm that was first published in 1990.

International Telecommunication Union-Telecommunications Standards Sector (ITU-TSS)
ITU-TSS is an intergovernmental organization that develops and adopts international treaties and telecommunications standards. ITU was founded in 1865 and became a United Nations agency in 1947.

Internet Control Message Protocol (ICMP)
ICMP is the portion of IP that handles network error control and diagnostic functions.

Internet Engineering Task Force (IETF)
IETF is a large, open, international community of network designers, operators, vendors, and researchers concerned with the evolution of the Internet architecture and smooth operation of the Internet.

Internet Group Management Protocol (IGMP)
IGMP is composed of software rules and procedures used by IP devices to report their multicast group memberships to an adjacent multicast router. IGMP helps routers identify these devices.

Internet Network Information Center (InterNIC)
InterNIC is responsible for registration of domain names for all sites outside the western hemisphere, in the following top-level domains: com, org, net, and edu. Western-hemisphere domain names are registered by ARIN.

Internet Protocol (IP)
IP is the protocol responsible for getting packets of information across a network.

Internet Protocol Control Protocol (IPCP)
IPCP describes how PPP encapsulates Network Layer information for transmission over a serial point-to-point link.

Internet Service Provider (ISP)
An ISP is an organization that provides Internet connectivity ranging from dedicated corporate connections to single-user dial-up services.

Internetwork
An internetwork is a complex network that may combine smaller networks in different physical locations, based on different types of network architectures.

Interoperability
Interoperability refers to the ability of different types of computers, networks, operating systems, and applications to work together effectively. An example of interoperability would be a Transmission Control Protocol (TCP) UNIX application using American Standard Code for Information Interchange (ASCII) text files exchanging data with an Extended Binary Coded Decimal Interchange Code (EBCDIC) IBM host.

Interpreter
An interpreter is a program that reads and executes programming script written in a high-level language. The interpreter reads a script line by line, then executes it line by line. See parser.

Interrupt
Interrupt is a signal that tells a program, or CPU, that an event has occurred. Interrupts are generated by applications (software interrupts) and devices (hardware interrupts).

IP Module
An IP module is IP software that resides in each host and router in the Internet system. IP modules share common rules for interpreting IP address fields and processing Internet packets. The IP process on one machine passes an Internet packet to the IP process on another machine, until the packet reaches its final destination.

IP Security (IPsec)
IPsec is a set of IETF protocols, under development, to support secure IP packet communication. When completed, IPsec is intended to implement VPNs.