Information Technology Reference
In-Depth Information
X.25 Configuration
Figure 5-4
Router A
s0: IP = 172.18.1.5/30
X.121 = 12121212
x25 map ip 172.18.1.6.34343434 broadcast
X.25 Network
X.121 = 34343434
172.18.1.6/30
Router B
Frame Relay
This section covers the Frame Relay topics that are listed in the blueprint of the CCIE
written test.
Frame Relay is a Layer-2 WAN service that sends information in frames. Each frame has an
address that the network uses to determine the destination of the frame. Frame Relay was
developed when lines became more reliable and the high-overhead link error checking that is
found in X.25 was no longer required. This provided more available bandwidth for WAN con-
nectivity. Similar to X.25, Frame Relay uses VCs. Frame Relay leaves the error checking to
higher layer protocols. Frame Relay was initially defined by the Frame Relay Forum. More
information and implementation agreements are at www.frforum.com.
As shown in Figure 5-5, router and other devices perform the function of DTE by connecting
to a Frame Relay switch that has a DCE interface. Although SVCs are possible with Frame
Relay, most implementations use PVCs.
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