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Glossary

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FragmentFree

LAN switch type that reads into the data section of a frame

to make sure fragmentation did not occur. Sometimes called modified cut-
through.

frame

A logical unit of information sent by the data link layer over a trans-

mission medium. The term often refers to the header and trailer, employed
for synchronization and error control, that surround the data contained in
the unit.

Frame Relay

A more efficient replacement of the X.25 protocol (an unre-

lated packet relay technology that guarantees data delivery). Frame Relay is
an industry-standard, shared-access, best-effort, switched data-link layer
encapsulation that services multiple virtual circuits and protocols between
connected mechanisms.

Frame Relay bridging

Defined in RFC 1490, this bridging method

uses the identical spanningtree algorithm as other bridging operations but
permits packets to be encapsulated for transmission across a Frame Relay
network.

Frame Relay switching

When a router at a service provider provides

packet switching for Frame Relay packets.

frame tagging

VLANs can span multiple connected switches, which

Cisco calls a switch-fabric. Switches within this switch-fabric must keep
track of frames as they are received on the switch ports, and they must
keep track of the VLAN they belong to as the frames traverse this switch-
fabric. Frame tagging performs this function. Switches can then direct frames
to the appropriate port.

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).

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