H-I

hashing

The process whereby an algorithm is used to distribute evenly into a number of possible buckets in a hash table.`

HICB

Hardware Interface Control Block. A root or anchor block for accessing the configuration, status, and statistics of a hardware interface.

high availability

A feature wherein the system is available for most of the time. A system usually implements high availability using various schemes. Using redundant components is one scheme.

high-level design

Often known as System Design. In this phase, the software system is broken into modules and tasks. This phase also specifies the interfaces between the various modules and tasks, along with global data structures.

host

An end node in a network. Hosts communicate with other hosts, sending their traffic through switches and routers if the other entity is on a different network.

hot standby

A redundancy scheme in which the standby card is initialized and receives updates from the primary card even while the primary is functional. This permits the standby card to take over very quickly when the primary card fails.

HTTP

HyperText Transfer Protocol. An application layer protocol for accessing web pages. HTTP runs over TCP and is often used to manage a communications device via a browser. See Web-based management.

ICCP

Inter-Card Communication Protocol. A protocol used for communications between the control card and line cards on top of the interconnect.

ICMP

Internet Control Message Protocol. Used for diagnostics and control messaging in the IP world.

IEEE

Institution of Electrical and Electronic Engineers. A body which also sets standards in various areas of networking. The IEEE 802 committee is the most relevant for networking. IEEE 802.3 is the Ethernet standard, while IEEE 802.11b, 11a, and 11g are the Wireless LAN standards.

IEEE 802.1D

The IEEE standard specifying the Spanning Tree Protocol for Layer 2 bridges.

IEEE 802.1Q

The IEEE standard specifying the VLAN registration protocol (GVRP) for exchange of VLAN registration information between bridges.

IEEE 802.3

The IEEE standard which specifies CSMA/CD-based Ethernet.

IETF

Internet Engineering Task Force. The body responsible for the specification of the protocols used in the Internet.

inter-process communication (IPC)

The mechanisms used for process-to-process communication. These can be determined by the operating system and can include message queues, mail boxes, shared memory, and so on.

interface

A term used to describe the layer of interaction between two modules and the procedures used on this layer.

interface

Used to describe a physical port of a system. See also Physical Interface and Logical Interface.

interop testing

Testing for determining the interoperability of the equipment and software with other vendor products. Generally, a requirement before a networking product is shipped.

interrupt processing

The opposite of polling. Processing occurs only if there is an interrupt, so there is no wasting of cycles due to polling.

interrupts

Events that tell the operating system to stop its current activity and take action.

IP

Internet Protocol. The protocol used in the Internet. It was originally specified by the IETF in RFC 791.

IPS

Acronym for an IP Switch. In the text, this is the Layer 3 IP Switch/Router—a device which performs IP forwarding.

IPSec

IP Security. A protocol used in IPv4 and IPv6 for securing IP communications between a sender and a receiver. IPSec involves both authentication and encryption.

IPX

Internetwork Packet Exchange. A Layer 3 protocol specified by Novell for communication between its Netware servers and clients. Several IPX networks have been deployed in enterprises.

ISDN

Integrated Services Digital Network. A set of protocols used to send voice and data over a network in digital format. Calls need to be set up before the voice or data transfer can take place.

IS–IS

Intermediate System–to–Intermediate System routing protocol developed originally by the ISO. It has been enhanced by the IETF for IP networks. The protocol is conceptually similar to the OSPF protocol in that it uses the Djikstra shortest-path- first (SPF) algorithm for calculating routes.

ISO

International Standards Organization. A body which publishes a set of standards for networking.

ISR

Interrupt Service Routine. The code that runs when the interrupt occurs.

ITU-T

A subcommittee of the International Telecommunications Union, a global body that drafts technical standards for all areas of communication. ITU-T has specified standards for SS7, X.25, and ATM.