3com NETBuilder SI Manual De Usuario

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 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.

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.