System information

Troubleshooting Frame Relay Connections 18-401
Network Implementation
Figure 18-4 Global Addressing Exchange
In Figure 16–4, note that each interface has its own identifier. Suppose that Pittsburgh must send a
frame to San Jose. The identifier for San Jose is 12, so Pittsburgh places the value 12 in the DLCI
field and sends the frame into the Frame Relay network. At the exit point, the DLCI field contents
are changed by the network to 13 to reflect the source node of the frame. Each router interface has a
distinct value as its node identifier, so individual devices can be distinguished. This permits adaptive
routing in complex environments.
Global addressing provides significant benefits in a large, complex internetwork. The Frame Relay
network now appears to the routers on its periphery like any LAN. No changes to higher-layer
protocols are needed to take full advantage of their capabilities.
Multicasting
Multicasting is another valuable optional LMI feature. Multicast groups are designated by a series
of four reserved DLCI values (1,019 to 1,022). Frames sent by a device using one of these reserved
DLCIs are replicated by the network and sent to all exit points in the designated set. The multicasting
extension also defines LMI messages that notify user devices of the addition, deletion, and presence
of multicast groups.
In networks that take advantage of dynamic routing, routing information must be exchanged among
many routers. Routing messages can be sent efficiently by using frames with a multicast DLCI. This
allows messages to be sent to specific groups of routers.
Network Implementation
Frame Relay can be used as an interface to either a publicly available carrier-provided service or to
a network of privately owned equipment. A typical means of private network implementation is to
equip traditional T1 multiplexers with Frame Relay interfaces for data devices, as well as non-Frame
Relay interfaces for other applications such as voice and video-teleconferencing. Figure 18–5 shows
this configuration.
San Jose
DLCI = 12
Pittsburgh
DLCI = 13
Los Angeles
DLCI = 14
Router
Atlanta
DLCI = 15
Switch
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WAN
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