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defines a point-to-point interaction between DTEs and DCEs. In simpler
terms, when it is time to transmit data, a terminal connects to a modem
or packet switch, which then connects to packet switching exchanges
(PSEs) and other DCEs to transmit the data to its final destination at
another terminal. The links by which data is transmitted are called virtual
circuits. Virtual circuits allow data transfers between two points on the
network through any number of nodes in the network.
Frame Relay Frame Relay provides a packet-switched network that
transfers data between DTEs, which can be routers, bridges, and host
computers, by creating virtual circuits and using DCEs to transfer the data
to its destination.
Frame Relay differs from X.25 (which was developed to work over
voice-grade telephone lines) because it was designed to make use of
today’s higher speed digital lines. Frame Relay has also been designed to
work within complex internetworking environments with extensions
referred to as the local management interface (LMI).
LMI provides information about all devices that are accessible on the
Frame Relay network by listing all data link connection identifiers (DLCIs)
connecting the local system with the remote ones. The LMI improves
reliability between the DTE and DCE through frequent exchange of
keepalive packets that contain status information.
IBM Legacy Networks Each serial port can be attached directly with a Flex-WAN cable to IBM
legacy equipment like mainframes and automatic teller machines. See
Table 4 for supported IBM protocols.