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Glossary

Frame Relay bridging

Defined in RFC 1490, this

bridging method uses the identical spanning-tree algo-
rithm as other bridging operations but permits packets
to be encapsulated for transmission across a Frame
Relay network.

framing

Encapsulation at the Data-Link layer of the

OSI model. It is called framing because the packet is
encapsulated with both a header and a trailer.

FRAS

Frame Relay Access Support: A feature of

Cisco IOS software that enables SDLC, Ethernet,
Token Ring, and Frame Relay-attached IBM devices
to be linked with other IBM mechanisms on a Frame
Relay network. See also: FRAD.

frequency

The number of cycles of an alternating

current signal per time unit, measured in hertz (cycles
per second).

FSIP

Fast Serial Interface Processor: The Cisco 7000

routers' default serial interface processor, it provides
four or eight high-speed serial ports.

FTP

File Transfer Protocol: The TCP/IP protocol

used for transmitting files between network nodes, it
supports a broad range of file types and is defined in
RFC 959. See also: TFTP.

full duplex

The capacity to transmit information

between a sending station and a receiving unit at the
same time. See also: half duplex.

full mesh

A type of network topology where every

node has either a physical or a virtual circuit linking it
to every other network node. A full mesh supplies a
great deal of redundancy but is typically reserved for
network backbones because of its expense. See also:
partial mesh.

GNS

Get Nearest Server: On an IPX network, a

request packet sent by a customer for determining the
location of the nearest active server of a given type. An
IPX network client launches a GNS request to get
either a direct answer from a connected server or a
response from a router disclosing the location of the
service on the internetwork to the GNS. GNS is part of
IPX and SAP. See also: IPX and SAP.

GRE

Generic Routing Encapsulation: A tunneling

protocol created by Cisco with the capacity for encap-
sulating a wide variety of protocol packet types inside
IP tunnels, thereby generating a virtual point-to-point

connection to Cisco routers across an IP network at
remote points. IP tunneling using GRE permits net-
work expansion across a single-protocol backbone
environment by linking multiprotocol subnetworks in
a single-protocol backbone environment.

guard band

The unused frequency area found

between two communications channels, furnishing the
space necessary to avoid interference between the two.

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.

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 and is the default encapsulation for Cisco rout-
ers. HDLC is a bit-oriented synchronous Data-Link
layer protocol created by ISO and derived from SDLC.
However, most HDLC vendor implementations
(including Cisco's) are proprietary. See also: SDLC.

helper address

The unicast address specified,

which instructs the Cisco router to change the client's
local broadcast request for a service into a directed
unicast to the server.

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

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