H


H.323

A videoconferencing standard developed by the International Telecommunication Union (ITU) that defines videoconferencing from the desktop over LANs, intranets, and the Internet.

H.323 specifies techniques for compressing and transmitting real-time voice, video, and data between a pair of videoconferencing workstations. It also describes signaling protocols for managing audio and video streams, as well as procedures for breaking data into packets and synchronizing transmissions across communications channels.

hacker

In the programming community, where the term originated, this term describes a person who pursues knowledge of computer systems for its own sake—someone willing to “hack through” the steps of putting together a working program.

More recently, in popular culture at large, the term has come to mean a person who breaks into other people’s computers with malicious intent (what programmers call a “cracker”). Many countries now treat convicted crackers in the same way that they treat conventional breaking-and-entering criminals.

half duplex

The capacity to transfer data in only one direction at a time between a sending unit and receiving unit. See also: full duplex.

handshake

Any series of transmissions exchanged between two or more devices on a network to ensure synchronized operations.

hardware address

The address assigned to a network interface card (NIC) by the original manufacturer or by the network administrator if the interface card is configurable.

This address identifies the local device address to the rest of the network and allows messages to find the correct destination. Also known as the physical address, media access control (MAC) address, or Ethernet address.

H channel

High-speed channel: A full duplex, ISDN primary rate channel operating at a speed of 384Kbps. See also: B, D, and E channels.

HDLC

High-Level Data Link Control: Using frame characters, including checksums, HDLC designates a method for data encapsulation on synchronous serial links. HDLC is a bit-oriented synchronous Data Link layer protocol created by ISO and derived from SDLC. See also: SDLC.

helper address

Used to send multicast addresses to a server on a remote network.

hierarchical addressing

Any addressing plan employing a logical chain of commands to determine location. IP addresses are made up of a hierarchy of network numbers, subnet numbers, and host numbers to direct packets to the appropriate destination.

HIP

HSSI Interface Processor: An interface processor used on Cisco 7000 series routers, providing one HSSI port that supports connections to ATM, SMDS, Frame Relay, or private lines at speeds up to T3 or E3.

holddown

The state a route is placed in so that routers can neither advertise the route nor accept advertisements about it for a defined time period. Holddown is used to surface bad information about a route from all routers in the network. A route is generally placed in holddown when one of its links fails.

hop

The movement of a packet between any two network nodes. See also: hop count.

hop count

A routing metric that calculates the distance between a source and a destination. RIP employs hop count as its sole metric. See also: hop and RIP.

host-based IDS (HIDS)

Installed locally on a host network device, host- based IDS systems are often better at preventing specific attacks than network IDS (NIDS) systems.

HSCI

High-Speed Communication Interface: Developed by Cisco, a single- port interface that provides full-duplex synchronous serial communications capability at speeds up to 52Mbps.

HSRP

Hot Standby Router Protocol: A protocol that provides high network availability and makes network topology changes without administrator intervention. It generates a Hot Standby router group, including a lead router that lends its services to any packet being transferred to the Hot Standby address. If the lead router fails, it will be replaced by any of the other routers—the standby routers—that monitor it.

HSSI

High-Speed Serial Interface: A network standard for high-speed serial linking over a WAN at speeds of up to 52Mbps.

hub

A device used to extend a network so that additional workstations can be attached. There are two main types of hubs:

Active hubs amplify transmission signals to extend cable length and ports.

Passive hubs split the transmission signal, allowing additional workstations to be added, usually at a loss of distance.

In some star networks, a hub is the central controlling device.

hybrid network

A network that uses a collection of different technologies, such as frame relay, leased lines, and X.25.




CCDA. Cisco Certified Design Associate Study Guide
CCDA: Cisco Certified Design Associate Study Guide, 2nd Edition (640-861)
ISBN: 0782142001
EAN: 2147483647
Year: 2002
Pages: 201

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