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Glossary

global command

Cisco term used to define commands that are used to

change the router configuration that affect the whole router. In contrast, an
interface command only affects that interface.

GMII

Gigabit MII: Media Independent Interface that provides 8 bits at

a time of data transfer.

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.

grafting

A process that activates an interface that has been deactivated

by the pruning process. It is initiated by an IGMP membership report sent
to the router.

GRE

Generic Routing Encapsulation: A tunneling protocol created by

Cisco with the capacity for encapsulating a wide variety of protocol packet
types inside IP tunnels, thereby generating a virtual point-to-point connec-
tion to Cisco routers across an IP network at remote points. IP tunneling
using GRE permits network 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 communica-

tions 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 channel, D channel, and
E channel.

HDLC

High-Level Data Link Control: Using frame characters, including

checksums, HDLC designates a method for data encapsulation on synchro-
nous serial links and is the default encapsulation for Cisco routers. HDLC is

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