H

Half duplex Data transmission that can occur in two directions over a single line, but only one direction at a time. Contrast full duplex.

HDLC (High-Speed Data Link Control) A protocol defined by the International Standards Organization and used in X.25 communications; specifies an encapsulation method for data on synchronous serial data links. Various manufacturers have proprietary versions of HDLC, including IBM's SDLC.

HEPCCC or HEP triple-C High Energy Physics Computing Consultative Committee.

Hierarchical routing Routing based on a hierarchical addressing system. IP routing algorithms use IP addresses, for example, which contain network numbers, host numbers and, frequently, subnet numbers.

HLM (Heterogenous LAN Management) Management of LANs that contain dissimilar devices running different protocols and different applications.

Hop A unit that equates to the passage of a packet through one router.

Hop Count A routing metric used to measure the distance between a source and a destination.

Host Any computer on the network that is a repository for services available to other computers on the network.

HPR High-Performance Routing

HPSN High-Performance Scalable Networking (3Com)

HSS High-Speed Serial

HSSI (High-Speed Serial Interface) A de facto standard for high-speed serial communications at up to 52 Mbps over WAN links.Used for the physical connection between a router and a DSU.

HTML Hyper Text Markup Language - the format of WWW documents.

HTSC HEPCCC Technical Sub Committee.

HTTP Hyper Text Transfer Protocol.

Hub The centre of a star topology network or cabling system.

Hyper-g A distributed hypertext system mostly popular in Europe.

Hyperlinks Connections between hypermedia or hypertext documents.

Hypermedia Hypertext documents that includes or links to others forms of media (eg sound or video).

Hypertext Text that, when selected, has the ability to present connected documents.