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Glossary

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Gigabit Ethernet

1000Mbps version of the IEEE 802.3. Fast Ethernet

offers a speed increase of 10 times that of the 10BaseT Ethernet specification
while preserving qualities such as frame format, MAC, mechanisms, and MTU.

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.

Group of Four

Used by Cisco Local Management Interface on Frame

Relay networks to manage the permanent virtual circuits (PVCs). See also: PVC.

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
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.

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