IAB Internet Architecture Board. Board of internetwork researchers who discuss issues pertinent to Internet architecture. Responsible for appointing a variety of Internet-related groups such as the IANA, IESG, and IRSG. The IAB is appointed by the trustees of the ISOC. See also IANA, IESG, IRSG, and ISOC. IANA Internet Assigned Numbers Authority. Organization operated under the auspices of the ISOC as a part of the IAB. IANA delegates authority for IP address-space allocation and domain-name assignment to the NIC and other organizations. IANA also maintains a database of assigned protocol identifiers used in the TCP/IP stack, including autonomous system numbers. See also IAB, ISOC, and NIC. ICC IDF that connects the horizontal cross-connect to the main cross-connect. See horizontal cross-connect. See main cross-connect. ICD International Code Designator. One of two ATM address formats developed by the ATM Forum for use by private networks. Adapted from the subnetwork model of addressing in which the ATM layer is responsible for mapping network layer addresses to ATM addresses. See also DCC. ICMP Internet Control Message Protocol. Network layer Internet protocol that reports errors and provides other information relevant to IP packet processing. Documented in RFC 792. ICMP Router Discovery Protocol See IRDP. Identification, Flags, Frag Offset Field within an IP datagram that provides fragmentation of datagrams to allow differing MTUs in the internet. IDF Intermediate distribution facility. Secondary communications room for a building using a star networking topology. The IDF is dependent on the MDF. See also MDF IDI Initial domain identifier. In OSI, the portion of the NSAP that specifies the domain. IDN International Data Number. See X.121. IDP Initial domain part. The part of a CLNS address that contains an authority and format identifier and a domain identifier. IDPR Interdomain Policy Routing. Interdomain routing protocol that dynamically exchanges policies between autonomous systems. IDPR encapsulates interautonomous system traffic and routes it according to the policies of each autonomous system along the path. IDPR is currently an IETF proposal. See also policy routing. IDRP IS-IS Interdomain Routing Protocol. OSI protocol that specifies how routers communicate with routers in different domains. IEC International Electrotechnical Commission. Industry group that writes and distributes standards for electrical products and components. IEEE Institute of Electrical and Electronics Engineers. Professional organization whose activities include the development of communications and network standards. IEEE LAN standards are the predominant LAN standards today. IEEE 802.1 IEEE specification that describes an algorithm that prevents bridging loops by creating a spanning tree. The algorithm was invented by Digital Equipment Corporation. The Digital algorithm and the IEEE 802.1 algorithm are not exactly the same, nor are they compatible. See also spanning tree, spanning-tree algorithm, and Spanning-Tree Protocol. IEEE 802.12 IEEE LAN standard that specifies the physical layer and the MAC sublayer of the data link layer. IEEE 802.12 uses the demand priority media-access scheme at 100 Mbps over a variety of physical media. See also 100VG-AnyLAN. IEEE 802.2 IEEE LAN protocol that specifies an implementation of the LLC sublayer of the data link layer. IEEE 802.2 handles errors, framing, flow control, and the network layer (Layer 3) service interface. Used in IEEE 802.3 and IEEE 802.5 LANs. See also IEEE 802.3 and IEEE 802.5. IEEE 802.3 IEEE LAN protocol that specifies an implementation of the physical layer and the MAC sublayer of the data link layer. IEEE 802.3 uses CSMA/CD access at a variety of speeds over a variety of physical media. Extensions to the IEEE 802.3 standard specify implementations for Fast Ethernet. Physical variations of the original IEEE 802.3 specification include 10Base2, 10Base5, 10BaseF, 10BaseT, and 10Broad36. Physical variations for Fast Ethernet include 100BaseT, 100BaseT4, and 100BaseX. IEEE 802.3i Physical variation of the original IEEE 802.3 specification that calls for using Ethernet type signaling over twisted pair networking media. The standard sets the signaling speed at 10 megabits per second using a baseband signaling scheme transmitted over twisted pair cable employing a star or extended star topology. See 10Base2, 10Base5, 10BaseF, 10BaseT, and 10Broad36. IEEE 802.4 IEEE LAN protocol that specifies an implementation of the physical layer and the MAC sublayer of the data link layer. IEEE 802.4 uses token-passing access over a bus topology and is based on the token bus LAN architecture. See also token bus. IEEE 802.5 IEEE LAN protocol that specifies an implementation of the physical layer and MAC sublayer of the data link layer. IEEE 802.5 uses token passing access at 4 or 16 Mbps over STP cabling and is similar to IBM Token Ring. See also Token Ring. IEEE 802.6 IEEE MAN specification based on DQDB technology. IEEE 802.6 supports data rates of 1.5 to 155 Mbps. See also DQDB. IESG Internet Engineering Steering Group. Organization, appointed by the IAB, that manages the operation of the IETF. See also IAB and IETF. IETF Internet Engineering Task Force. Task force consisting of over 80 working groups responsible for developing Internet standards. The IETF operates under the auspices of ISOC. See also ISOC. IFIP International Federation for Information Processing. Research organization that performs OSI prestandardization work. Among other accomplishments, IFIP formalized the original MHS model. See also MHS. IGMP Internet Group Management Protocol. Used by IP hosts to report their multicast group memberships to an adjacent multicast router. See also multicast router. IGP Interior Gateway Protocol. Internet protocol used to exchange routing information within an autonomous system. Examples of common Internet IGPs include IGRP, OSPF, and RIP. See also IGRP, OSPF, and RIP. IGRP Interior Gateway Routing Protocol. IGP developed by Cisco to address the problems associated with routing in large, heterogeneous networks. Compare with Enhanced IGRP. See also IGP, OSPF, and RIP. IIH IS-IS Hello. Message sent by all IS-IS systems to maintain adjacencies. See also IS-IS. IITA Information Infrastructure Technology and Applications. Component of the HPCC program intended to ensure U.S. leadership in the development of advanced information technologies. See also HPCC. ILMI Interim Local Management Interface. Specification developed by the ATM Forum for incorporating network-management capabilities into the ATM UNI. IMP Interface message processor. Old name for ARPANET packet switches. An IMP is now referred to as a PSN (packet-switch node). See also PSN (packet-switch node). in-band signaling Transmission within a frequency range normally used for information transmission. Compare with out-of-band signaling. Industry-Standard Architecture See ISA. Information Infrastructure Technology and Applications See IITA. infrared Electromagnetic waves whose frequency range is above that of microwaves, but below that of the visible spectrum. LAN systems based on this technology represent an emerging technology. initial domain identifier See IDI. initial domain part See IDP. INOC Internet Network Operations Center. BBN group that in the early days of the Internet monitored and controlled the Internet core gateways (routers). INOC no longer exists in this form. input/output See I/O. Institute of Electrical and Electronics Engineers See IEEE. insulator Any material with a high resistance to electrical current. See conductor. insured burst The largest burst of data above the insured rate that will be temporarily allowed on a PVC and not tagged by the traffic policing function for dropping in the case of network congestion. The insured burst is specified in bytes or cells. Compare with maximum burst. See also insured rate. insured rate The long-term data throughput, in bits or cells per second, that an ATM network commits to support under normal network conditions. The insured rate is 100 percent allocated; the entire amount is deducted from the total trunk bandwidth along the path of the circuit. Compare with excess rate and maximum rate. See also insured burst. insured traffic Traffic within the insured rate specified for the PVC. This traffic should not be dropped by the network under normal network conditions. See also CLP and insured rate. Integrated IS-IS Routing protocol based on the OSI routing protocol IS-IS, but with support for IP and other protocols. Integrated IS-IS implementations send only one set of routing updates, making it more efficient than two separate implementations. Formerly referred to as Dual IS-IS. Compare with IS-IS. Integrated Services Digital Network See ISDN. interarea routing Term used to describe routing between two or more logical areas. Compare with intra-area routing. Interdomain Policy Routing See IDPR. interface 1. Connection between two systems or devices. 2. In routing terminology, a network connection. 3. In telephony, a shared boundary defined by common physical interconnection characteristics, signal characteristics, and meanings of interchanged signals. 4. The boundary between adjacent layers of the OSI model. interface message processor See IMP. interface module Combination of a line card and an access card that together allow you to connect a LightStream 2020 ATM switch to other devices. interface processor Any of a number of processor modules used in the Cisco 7000 series routers. See AIP, CIP, EIP, FEIP, FIP, FSIP, HIP, MIP, SIP (Serial Interface Processor), and TRIP. interference Unwanted communication channel noise. Interim Local Management Interface See ILMI. Interior Gateway Protocol See IGP. Interior Gateway Routing Protocol See IGRP. intermediate cross connect See ICC. intermediate distribution facility See IDF. intermediate routing node See IRN. Intermediate Session Routing See ISR. intermediate system See IS. Intermediate System-to-Intermediate System See IS-IS. International Code Designator See ICD. International Data Number See X.121. International Electrotechnical Commission See IEC. International Federation for Information Processing See IFIP. International Organization for Standardization See ISO. International Standards Organization Erroneous expansion of the acronym ISO. See ISO. International Telecommunication Union Telecommunication Standardization Sector See ITU-T. Internet Term used to refer to the largest global internetwork, connecting tens of thousands of networks worldwide and having a "culture" that focuses on research and standardization based on real-life use. Many leading-edge network technologies come from the Internet community. The Internet evolved in part from ARPANET. At one time, called the DARPA Internet. Not to be confused with the general term internet. See also ARPANET. internet Short for internetwork. Not to be confused with the Internet. See internetwork. Internet Architecture Board See IAB. Internet address See IP address. Internet Assigned Numbers Authority See IANA. Internet Control Message Protocol See ICMP. Internet Engineering Steering Group See IESG. Internet Engineering Task Force See IETF. Internet Group Management Protocol See IGMP. Internet Network Operations Center See INOC. Internet Protocol See IP. Internet protocol Any protocol that is part of the TCP/IP protocol stack. See TCP/IP. Internet Research Steering Group See IRSG. Internet Research Task Force See IRTF. Internet Society See ISOC. internetwork Collection of networks interconnected by routers and other devices that functions (generally) as a single network. Sometimes called an internet, which is not to be confused with the Internet. internetworking General term used to refer to the industry that has arisen around the problem of connecting networks together. The term can refer to products, procedures, and technologies. Internetwork Packet Exchange See IPX. interNIC Organization that serves the Internet community by supplying user assistance, documentation, training, registration service for Internet domain names, and other services. Formerly called Network Information Center (NIC). interoperability Ability of computing equipment manufactured by different vendors to communicate with one another successfully over a network. Inter-Switching System Interface See ISSI. intra-area routing Term used to describe routing within a logical area. Compare with interarea routing. Inverse Address Resolution Protocol See Inverse ARP. Inverse ARP Inverse Address Resolution Protocol. Method of building dynamic routes in a network. Allows an access server to discover the network address of a device associated with a virtual circuit. I/O input/output. IOS See Cisco IOS software. IP Internet Protocol. Network layer protocol in the TCP/IP stack offering a connectionless internetwork service. IP provides features for addressing, type-of-service specification, fragmentation and reassembly, and security. Documented in RFC 791. IP access-group Command that links an existing access list to an outbound interface. IP address 1.) 32-bit address assigned to hosts using TCP/IP. An IP address belongs to one of five classes (A, B, C, D, or E) and is written as 4 octets separated with periods (dotted decimal format). Each address consists of a network number, an optional subnetwork number, and a host number. The network and subnetwork numbers together are used for routing, while the host number is used to address an individual host within the network or subnetwork. A subnet mask is used to extract network and subnetwork information from the IP address. Also called an Internet address. 2.) Command used to establish the logical network address of this interface. See also IP and subnet mask. IP host Command used to make a static name-to-address entry in the router’s configuration file. IP multicast Routing technique that allows IP traffic to be propagated from one source to a number of destinations or from many sources to many destinations. Rather than sending one packet to each destination, one packet is sent to a multicast group identified by a single IP destination group address. IP name-server Command used to define which hosts can provide the name service. IP options Field within an IP datagram that deals with network testing, debugging, security, and others. IP Security Option See IPSO. IPSO IP Security Option. U.S. government specification that defines an optional field in the IP packet header that defines hierarchical packet security levels on a per interface basis. IPX Internetwork Packet Exchange. NetWare network layer (Layer 3) protocol used for transferring data from servers to workstations. IPX is similar to IP and XNS. IPXWAN Protocol that negotiates end-to-end options for new links. When a link comes up, the first IPX packets sent across are IPXWAN packets negotiating the options for the link. When the IPXWAN options have been successfully determined, normal IPX transmission begins. Defined by RFC 1362. IRDP ICMP Router Discovery Protocol. Enables a host to determine the address of a router that it can use as a default gateway. Similar to ESIS, but used with IP. See also ES-IS. IRN Intermediate routing node. In SNA, a subarea node with intermediate routing capability. IRSG Internet Research Steering Group. Group that is part of the IAB and oversees the activities of the IRTF. See also IAB and IRTF. IRTF Internet Research Task Force. Community of network experts that consider Internet-related research topics. The IRTF is governed by the IRSG and is considered a subsidiary of the IAB. See also IAB and IRSG. IS Intermediate system. Routing node in an OSI network. ISA Industry-Standard Architecture. 16-bit bus used for Intel-based personal computers. See also EISA. isarithmic flow control Flow control technique in which permits travel through the network. Possession of these permits grants the right to transmit. Isarithmic flow control is not commonly implemented. ISDN Integrated Services Digital Network. Communication protocol, offered by telephone companies, that permits telephone networks to carry data, voice, and other source traffic. See also BISDN, BRI, N-ISDN, and PRI. IS-IS Intermediate System-to-Intermediate System. OSI link-state hierarchical routing protocol based on DECnet Phase V routing whereby ISs (routers) exchange routing information based on a single metric to determine network topology. Compare with Integrated IS-IS. See also ES-IS and OSPF. IS-IS Hello See IIH. IS-IS Interdomain Routing Protocol See IDRP. ISO International Organization for Standardization. International organization that is responsible for a wide range of standards, including those relevant to networking. ISO developed the OSI reference model, a popular networking reference model. ISO 3309 HDLC procedures developed by ISO. ISO 3309:1979 specifies the HDLC frame structure for use in synchronous environments. ISO 3309:1984 specifies proposed modifications to allow the use of HDLC in asynchronous environments as well. ISO 9000 Set of international quality-management standards defined by ISO. The standards, which are not specific to any country, industry, or product, allow companies to demonstrate that they have specific processes in place to maintain an efficient quality system. ISOC Internet Society. International nonprofit organization, founded in 1992, that coordinates the evolution and use of the Internet. In addition, ISOC delegates authority to other groups related to the Internet, such as the IAB. ISOC is headquartered in Reston, Virginia, U.S.A. See also IAB. isochronous transmission Asynchronous transmission over a synchronous data link. Isochronous signals require a constant bit rate for reliable transport. Compare with asynchronous transmission, plesiochronous transmission, and synchronous transmission. ISODE ISO development environment. Large set of libraries and utilities used to develop upper-layer OSI protocols and applications. ISO development environment See ISODE. ISR Intermediate Session Routing. Initial routing algorithm used in APPN. ISR provides node-to-node connection-oriented routing. Network outages cause sessions to fail because ISR cannot provide nondisruptive rerouting around a failure. ISR has been replaced by HPR. Compare with HPR. See also APPN. ISSI Inter-Switching System Interface. Standard interface between SMDS switches. ITU-T International Telecommunication Union Telecommunication Standardization Sector (ITU-T) (formerly the Committee for Internatiional Telegraph and Telephone ([CCITT]). An international organization that develops communication standards. See also CCITT.