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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.
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.
The capacity to transfer data in only one direction at a time between a sending unit and receiving unit. See also: full duplex.
Any series of transmissions exchanged between two or more devices on a network to ensure synchronized operations.
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.
High-speed channel: A full duplex, ISDN primary rate channel operating at a speed of 384Kbps. See also: B, D, and E channels.
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.
Used to send multicast addresses to a server on a remote network.
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.
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.
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.
The movement of a packet between any two network nodes. See also: 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.
Installed locally on a host network device, host- based IDS systems are often better at preventing specific attacks than network IDS (NIDS) systems.
High-Speed Communication Interface: Developed by Cisco, a single- port interface that provides full-duplex synchronous serial communications capability at speeds up to 52Mbps.
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.
High-Speed Serial Interface: A network standard for high-speed serial linking over a WAN at speeds of up to 52Mbps.
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.
A network that uses a collection of different technologies, such as frame relay, leased lines, and X.25.
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