Internetworking Terms

Signal looped back toward the incoming facility.

Area in which a failure occurred in a Token Ring, defined by the information contained in a beacon. When a station detects a serious problem with the network (such as a cable break), it sends a beacon frame that includes the station reporting the failure, its NAUN, and everything in between. Beaconing in turn initiates a process called autoreconfiguration. See also autoreconfiguration, beacon, and NAUN.

Mechanism used by ATM networks when rigorous path selection does not generate an acceptable path. The fallback mechanism attempts to determine a path by selectively relaxing certain attributes, such as delay, in order to find a path that meets some minimal set of desired attributes.

Device that allows multiple devices on a network to communicate using a single network attachment.

Panel of I/O connectors that attaches to an equipment rack, providing easy access for data connections to a network.

frequently asked questions. Usually appears in the form of a "read-me" file in a variety of Internet forums. New users are expected to read the FAQ before participating in newsgroups, bulletin boards, video conferences, and so on.

Federation of American Research NETworks.

Any of a number of 100-Mbps Ethernet specifications. Fast Ethernet offers a speed increase 10 times that of the 10BaseT Ethernet specification while preserving such qualities as frame format, MAC mechanisms, and MTU. Such similarities allow the use of existing 10BaseT applications and network management tools on Fast Ethernet networks. Based on an extension to the IEEE 802.3 specification. Compare with EtherChannel. See also 100BaseFX, 100BaseT, 100BaseT4, 100BaseTX, 100BaseX, and IEEE 802.3.

See FEIP in the "Cisco Systems Terms and Acronyms" section.

See FST in the "Cisco Systems Terms and Acronyms" section.

See FSIP in the "Cisco Systems Terms and Acronyms" section.

See fast switching in the "Cisco Systems Terms and Acronyms" section.

One of five categories of network management defined by ISO for management of OSI networks. Fault management attempts to ensure that network faults are detected and controlled. See also accounting management, configuration management, performance management, and security management.

Federal Communications Commission. U.S. government agency that supervises, licenses, and controls electronic and electromagnetic transmission standards.

first come first served.

frame check sequence. Extra characters added to a frame for error control purposes. Used in HDLC, Frame Relay, and other data link layer protocols.

Fiber Distributed Data Interface. LAN standard, defined by ANSI X3T9.5, specifying a 100-Mbps token-passing network using fiber-optic cable, with transmission distances of up to 2 km. FDDI uses a dual-ring architecture to provide redundancy. Compare with CDDI and FDDI II.

ANSI standard that enhances FDDI. FDDI II provides isochronous transmission for connectionless data circuits and connection-oriented voice and video circuits. Compare with FDDI.

See FIP in the "Cisco Systems Terms and Acronyms" section.

Apple Computer's data-link product that allows an AppleTalk network to be connected by FDDI cable.

Facility Data Link. A 4-kbps channel provided by the Extended Superframe (ESF) T1 framing format. The FDL performs outside the payload capacity and allows a service provider to check error statistics on terminating equipment without intrusion.

frequency-division multiplexing. Technique whereby information from multiple channels can be allocated bandwidth on a single wire based on frequency. Compare with ATDM, statistical multiplexing, and TDM.

Fast Ethernet.

Modular system cards that perform specific functionality (DSC cards or modem cards, for example).

forward error correction. FEC is a class of methods for controlling errors in a one-way communication system. FEC sends extra information along with the data, which can be used by the receiver to check and correct the data.

forward explicit congestion notification. Bit set by a Frame Relay network to inform DTE receiving the frame that congestion was experienced in the path from source to destination. DTE receiving frames with the FECN bit set can request that higher-level protocols take flow-control action as appropriate. Compare with BECN.

See FCC.

See FNC.

See FEIP in the "Cisco Systems Terms and Acronyms" section.

front-end processor. Device or board that provides network interface capabilities for a networked device. In SNA, typically an IBM 3745 device.

Feature Group-D (FGD). Identifies a standardized service available to carriers delivered on a channelized T1 line.

Feature Group-D (FGD) signalling protocol of type Exchange Access North American (EANA). This provides certain call services, such as emergency (USA-911) calls. The command calling number outbound is used only for FGD-EANA signalling to generate ANI digits for outgoing calls.

See FDDI.

A method for the transmission of information (audio, video, data). Light is modulated and transmitted over high purity, hair-thin fibers of glass. The bandwidth capacity of fiber optic cable is much greater than that of conventional cable or copper wire.

Aerial or buried fiber optic cable that established connectivity between fiber optic transmission equipment locations.

Physical medium capable of conducting modulated light transmission. Compared with other transmission media, fiber-optic cable is more expensive but is not susceptible to electromagnetic interference, and is capable of higher data rates. Sometimes called optical fiber.

See FOIRL.

fiber connectivity. FICON channels provide 100-Mbps bi-directional link rates at unrepeated distances of up to 20 km over fiber optic cables (compared with ESCON channels that support 17-MBps link rates at maximum unrepeated distances of up to 3 km).

format indicator 0. One of several formats that an SNA TH can use. An FID0 TH is used for communication between an SNA node and a non-SNA node. See also TH.

format indicator 1. One of several formats that an SNA TH can use. An FID1 TH encapsulates messages between two subarea nodes that do not support virtual and explicit routes. See also TH.

format indicator 2. One of several formats that an SNA TH can use. An FID2 TH is used for transferring messages between a subarea node and a PU 2, using local addresses. See also TH.

format indicator 3. One of several formats that an SNA TH can use. An FID3 TH is used for transferring messages between a subarea node and a PU 1, using local addresses. See also TH.

format indicator 4. One of several formats that an SNA TH can use. An FID4 TH encapsulates messages between two subarea nodes that are capable of supporting virtual and explicit routes. See also TH.

Hardware component that can be removed and replaced on-site. Typical field-replaceable units include cards, power supplies, and chassis components.

first-in, first-out. Refers to a buffering scheme where the first byte of data entering the buffer is the first byte retrieved by the CPU. In telephony, FIFO refers to a queueing scheme where the first calls received are the first calls processed.

first-in, first-out queueing. Involves buffering and forwarding of packets in the order of arrival. FIFO embodies no concept of priority or classes of traffic. There is only one queue, and all packets are treated equally. Packets are sent out an interface in the order in which they arrive.

Category of popular network applications that allow files to be moved from one network device to another.

See FTP.

See FTAM.

Generally, a process or a device that screens network traffic for certain characteristics, such as source address, destination address, or protocol, and determines whether to forward or discard that traffic based on the established criteria.

Internetwork router that selectively prevents the passage of data packets according to a security policy.

Software tool for determining whether a person has an account at a particular Internet site. Many sites do not allow incoming finger requests.

See FIP (FDDI Interface Processor) in the "Cisco Systems Terms and Acronyms" section.

Router or access server, or several routers or access servers, designated as a buffer between any connected public networks and a private network. A firewall router uses access lists and other methods to ensure the security of the private network.

Software instructions set permanently or semipermanently in ROM.

Fill-In Signal Unit. SS7 message that is sent in both directions whenever other signal units are not present. Provides a CRC checksum for use by both signalling endpoints.

Federal Internet Exchange. Connection point between the North American governmental internets and the Internet. The FIXs are named after their geographic region, as in FIX West (Mountain View, California) and FIX East (College Park, Maryland). See also CIX, GIX, and MAE.

Routing problem where an advertised route between two nodes alternates (flaps) back and forth between two paths due to a network problem that causes intermittent interface failures.

A special type of EEPROM that can be erased and reprogrammed in blocks instead of one byte at a time. Many modern PCs have their BIOS stored on a flash memory chip so that it can be updated easily if necessary. Such a BIOS is sometimes called a flash BIOS. Flash memory is also popular in modems because it enables the modem manufacturer to support new protocols as they become standardized.

Routing update sent asynchronously in response to a change in the network topology. Compare with routing update.

Scheme of addressing that does not use a logical hierarchy to determine location. For example, MAC addresses are flat, so bridging protocols must flood packets throughout the network to deliver the packet to the appropriate location. Compare with hierarchical addressing.

SS7 fully associated link. An SS7 signaling link directly associated with a link carrying traffic (although not necessarily imbedded within the same physical span.

Traffic passing technique used by switches and bridges in which traffic received on an interface is sent out all the interfaces of that device except the interface on which the information was receivedoriginally.

Stream of data traveling between two endpoints across a network (for example, from one LAN station to another). Multiple flows can be transmitted on a single circuit.

Technique for ensuring that a transmitting entity, such as a modem, does not overwhelm a receiving entity with data. When the buffers on the receiving device are full, a message is sent to the sending device to suspend the transmission until the data in the buffers has been processed. In IBM networks, this technique is called pacing.

In IPv6, the traffic parameters of a stream of IP packets between two applications. See also IPv6.

Full Line Terminal. Multiplexer that terminates a SONET span. See also SONET.

frequency modulation. Modulation technique in which signals of different frequencies represent different data values. Compare with  AM and PAM. See also modulation.

Federal Networking Council. Group responsible for assessing and coordinating U.S. federal agency networking policies and needs.

fiber-optic interrepeater link. Fiber-optic signaling methodology based on the IEEE 802.3 fiber-optic specification. FOIRL is a precursor of the 10BaseFL specification, which is designed to replace it. See also 10BaseFL.

Geographical area in which an entity is licensed to broadcast its signal.

See FX.

See FID0.

See FID1.

See FID2.

See FID3.

See FID4.

Communications path carrying information from the call initiator to the called party.

Amount of time an interface spends listening for topology change information after that interface is activated for bridging and before forwarding actually begins.

See FE.

Process of sending a frame toward its ultimate destination by way of an internetworking device.

Fiber Optics Transmission Systems. Vendor-proprietary fiber-optic transmission equipment.

Technique used to evaluate the importance of various frequency cycles in a time series pattern.

See dot address.

fully qualified domain name. FQDN is the full name of a system, rather than just its host name. For example, aldebaran is a host name, and aldebaran.interop.com is an FQDN.

See channelized T1.

Frame Relay access device. Any network device that provides a connection between a LAN and a Frame Relay WAN. See also Cisco FRAD (Cisco Frame Relay access device) and FRAS (Frame Relay access support) in the "Cisco Systems Terms and Acronyms" section.

Piece of a larger packet that has been broken down to smaller units.

Process of breaking a packet into smaller units when transmitting over a network medium that cannot support the original size of the packet. See also reassembly.

Logical grouping of information sent as a data link layer unit over a transmission medium. Often refers to the header and the trailer, used for synchronization and error control, that surround the user data contained in the unit. The terms cell, datagram, message, packet, and segment also are used to describe logical information groupings at various layers of the OSI reference model and in various technology circles.

See FCS.

Mechanism by which frame-based traffic, such as HDLC and SDLC, traverses an ATM network.

Industry-standard, switched data link layer protocol that handles multiple virtual circuits using HDLC encapsulation between connected devices. Frame Relay is more efficient than X.25, the protocol for which it generally is considered a replacement. See also X.25.

See FRAD.

See FRAS in the "Cisco Systems Terms and Acronyms" section.

Bridging technique, described in RFC 1490, that uses the same spanning-tree algorithm as other bridging functions but allows packets to be encapsulated for transmission across a Frame Relay network.

See LAN switch.

See FRAS (Frame Relay access support) in the "Cisco Systems Terms and Acronyms" section.

Frame Relay access service module.

Community-based bulletin board system with e-mail, information services, interactive communications, and conferencing.

Part of an AppleTalk internetwork that is accessible by two other parts of the internetwork that cannot directly access one another.

Number of cycles per second, measured in hertz, of an alternating current.

See FM.

One of the fundamental concepts on which commercial wireless systems are based that involves the partitioning of an RF radiating area (cell) into segments of a cell, which for Cisco purposes means the cell is broken into three equal segments. One segment of the cell uses a frequency that is far enough away from the frequency in the bordering segment that it does not provide interference problems.

Frequency re-use in mobile cellular systems means that each cell has a frequency that is far enough away from the frequency in the bordering cell that it does not provide interference problems. The same frequency is used at least two cells apart from each other. This practice enables cellular providers to have many times more customers for a given site license.

See FDM.

Frame Relay Forum. An association of corporate members consisting of vendors, carriers, users, and consultants committed to the implementation of Frame Relay in accordance with national and international standards. See www.frforum.com.

Frame Relay Forum implementation agreement for Voice over Frame Relay (v1.0 May 1997). This specification defines multiplexed data, voice, fax, DTMF digit-relay, and CAS/Robbed-bit signaling frame formats but does not include call setup, routing, or administration facilities. See www.frforum.com.

See FRF.12.

The FRF.12 Implementation Agreement (also known as FRF.11 Annex C) was developed to allow long data frames to be fragmented into smaller pieces and interleaved with real-time frames. In this way, real-time voice and non real-time data frames can be carried together on lower speed links without causing excessive delay to the real-time traffic. See www.frforum.com.

Frame Relay-to-ATM Service Interworking. To communicate over WANs, end-user stations and the network cloud typically must use the same type of transmission protocol. This limitation has prevented differing networks, such as Frame Relay and ATM, from being linked. However, the Frame Relay-to-ATM Service Interworking (FRF.8) feature allows Frame Relay and ATM networks to exchange data despite differing network protocols. The Frame Relay/ATM PVC Service Interworking Implementation Agreement specified in Frame Relay Forum (FRF) document number FRF.8 provide the functional requirements for linking Frame Relay and ATM networks.

Point to point permanent voice connection (private line) conforming to the FRF.11 specification.

Frame REJECT.

Node or software program that requests services of a back end. See also back end, client, and server.

See FEP.

Frame Relay traffic shaping. Queueing method that uses queues on a Frame Relay network to limit surges that can cause congestion. Data is buffered and sent into the network in regulated amounts to ensure that the traffic can fit within the promised traffic envelope for the particular connection.

See FSIP in the "Cisco Systems Terms and Acronyms" section.

Forward Sequence Number. Part of an SS7 MSU that contains the sequence number of the signal unit.

Fast Simple Server Redundancy Protocol. The LANE simple server redundancy feature creates fault-tolerance using standard LANE protocols and mechanisms. FSSRP differs from LANE SSRP in that all configured LANE servers of an Emulated LAN (ELANE) are always active. See also SSRP.

See FST in the "Cisco Systems Terms and Acronyms" section.

File Transfer, Access, and Management. In OSI, an application layer protocol developed for network file exchange and management between diverse types of computers.

File Transfer Protocol. Application protocol, part of the TCP/IP protocol stack, used for transferring files between network nodes. FTP is defined in RFC 959.

Capability for simultaneous data transmission between a sending station and a receiving station. Compare with half duplex and simplex.

Term describing a network in which devices are organized in a mesh topology, with each network node having either a physical circuit or a virtual circuit connecting it to every other network node. A full mesh provides a great deal of redundancy but because it can be prohibitively expensive to implement, it usually is reserved for network backbones. See also mesh and partial mesh.

See FQDN.

frame user network interface.

Digital Equipment Corporation LSI-11 computer system running IP gateway software. The NSFnet used these systems as backbone packet switches.

foreign exchange.

1. A circuit that connects a subscriber in one exchange with a central office (CO) in another exchange.

2. A trunk type that connects a call center with a central office in a remote exchange. This allows callers in that remote exchange. See also CO, FXO, FXS, and PBX.

Foreign Exchange Office. An FXO interface connects to the Public Switched Telephone Network (PSTN) central office and is the interface offered on a standard telephone. Cisco's FXO interface is an RJ-11 connector that allows an analog connection at the PSTN's central office or to a station interface on a PBX.

Foreign Exchange Station. An FXS interface connects directly to a standard telephone and supplies ring, voltage, and dial tone. Cisco's FXS interface is an RJ-11 connector that allows connections to basic telephone service equipment, keysets, and PBXs.