understand and review Frame Relay terminology. We will describe common components of
Frame Relay networks such as LMI and BECN and look at various topology options in the
design, including multipoint versus point-to-point interfaces. We will take a look at advantages
and disadvantages, access devices and services, and switching operations together with the
LMI. The discussion will include how Cisco routers fit into the picture, Cisco routers and RFC
1490, DLCI mapping and inverse ARP, and design ideas.
circuits are the key. Figure 10-12 also shows a 64K point-to-point circuit from New York to Los
Angeles. As you add a new circuit for Chicago, you have to add another port to the router at
New York and another CSU/DSU. By adding circuits in this manner, the possibility exists that
there will be a lot of redundancy. There also will be many port costs and circuit costs (which
are the most expensive). Multiple access lines will go into the routers--a major portion of the
circuit costs.
speeds are achieved because Frame Relay does not do error checking. Frame Relay depends on
the upper layers of the OSI model to guarantee delivery of data and do error checking. The
disadvantage of Frame Relay as compared to X.25 is that Frame Relay can not reroute around
network failures. It typically relies on IP to handle that. See Example 10-3.
interface Serial0
ip address 192.168.100.1 255.255.255.0
encapsulation frame-relay
no ip mroute-cache
frame-relay map ip 192.168.100.2 102 broadcast
frame-relay map ip 192.168.100.3 103 broadcast
C 192.168.100.0/24 is directly connected, Serial0
interface Serial0
ip address 192.168.100.2 255.255.255.0
encapsulation frame-relay
frame-relay map ip 192.168.100.1 104 broadcast
frame-relay interface-dlci 104
no frame-relay inverse-arp
chicago#sh ip rou
C 192.168.100.0/24 is directly connected, Serial0
interface Serial0
ip address 192.168.100.3 255.255.255.0
no ip directed-broadcast