IBM SC30-3681-08 manual Frame Relay Network, Using Frame Relay, Management

Using Frame Relay

Frame Relay Network

The FR network consists of the FR backbone (consisting of FR switches provided by the FR carrier) providing the FR service. The router functions as the FR connection device. The router encapsulates FR frames and routes them through the network based on a Data Link Connection Identi®er (DLCI). The DLCI is the

medium access control (MAC) address that identi®es the PVC or SVCbetween the router and the FR destination device. For example, in Figure 21, a packet destined to go from router B to router D would have a DLCI of 19 to reach router D; however, a packet destined to go from router D to router B would have a DLCI of 16.

	DLCI 19	Frame
		Relay
Router		Backbone
B

physical connection
logical connection	DLCI 18

Router

A

Figure 21. DLCIs in Frame Relay Network

DLCI 16
DLCI 17	Router
	D

A DLCI can have either local or global signi®cance. Local DLCIs are signi®cant at

the point of entry to the network, but global DLCIs are signi®cant throughout the

network. To the user, however, the DLCI that the router uses to route a packet is

the DLCI that the user associates with the frame's global or local destination. DLCIs

are con®gured through the FR con®guration process or learned through FR

management.

FR PVCs are prede®ned connections used to route data through a FR network. The

bandwidth allocated for a PVC within the network is a subscription option and must

be allotted to the PVC whether or not the PVC uses it.

A Frame Relay network has the following characteristics:

vTransports frames transparently. The network can modify only the DLCI, congestion bits, and frame check sequence. High-Level Data Link Control (HDLC) ¯ags and zero bit insertion provide frame delimiting, alignment, and transparency.

vDetects transmission, format, and operational errors (frames with an unknown DLCI)

388MRS V3.2 Software User's Guide