H.323 Multimedia Conferencing Standard

H.323 is part of a family of ITU-T recommendations that specify multimedia communications services such as real-time audio, video, and data over a variety of communication services, including videoconference. H.323 defines multimedia communications over packet-switched   networks using desktop computers or audiovisual devices. Audio is a required component, while video and data are optional. Since packet-switched networks are not good at supporting real-time audio and video, H.323 addresses problems related to packet delay and packet loss on           

Handshake

See Connection Establishment.

HDLC (High-Level Data Link Control)  

HDL Cisabit-oriented, link layer protocol for the transmission of data over synchronous networks .It is an ISO standard, but is a superset of IBM’s SDLC(Synchronous Data Link Control)  protocol. SDLC was the successful follow-up to the BISYNC communication protocol and was originally introduced with IBM SNA(Systems Network Architecture) products. Another name for HDLC is ADCCP(Advanced Data Communications Control Procedure),an ANSI standard, but HDLC is the widely accepted name for the protocol. There are some incompatibilities between SDLC and HDLC, depending on the vendor.      

HDSL (High-Bit-Rate Digital Subscriber Line)

HDSL is one of the DSL (Digital Subscriber Line) options that permits high-speed data transmissions over the existing copper-based lines that provide telephone service between most homes and the telephone companies’ central offices.

High-Speed/High-Performance Networking

“High-speed networking” is a misnomer. Speed seems to imply that bits are moving faster. People use the term when they are really talking about high-performance networks with high data rates. A network medium that operates at gigabit/sec rates is perceived as fast because a typical file transfer occurs in a very short period of time compared to transferring the same file over a modem link, for example. “Fast” is based on user perception.

HSRP (Hot Standby Router Protocol)

HSRP is a Cisco protocol that switches to a backup router if a main router fails. The protocol provides automatic router backup (fault tolerance). HSRP is compatible with IP, Novell’s Internet work Packet Exchange (IPX), AppleTalk, and Banyan VINES, and it is compatible with DECnet and Xerox Network Systems (XNS) in certain configurations. In a WAN configuration, HSRP can provide a way to forward packets on an alternate link should a primary link fail. HSRP is defined in RFC 2281, “Cisco Hot Standby Router Protocol,” (March 1998)and at the Cisco Web site (see address following).