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166 Chapter 6: Using ISDN and DDR Technologies
In Example 6-27 and 6-28, RouterA is defined as the server router and RouterB is defined as
the client router. In this scenario, the quiet timer is slowly counting down to zero. Once the quiet
period timer expires, the client router dials the server router. The defined quiet period is 12
hours (actually 720 minutes). Once the 12 hours have elapsed, the client and server routers
"thaw" their routing tables and exchange updates for the duration of the active period, in this
case, five minutes.
The active periods defined must match on both server and client routers. Five minutes is the
minimum active period you can configure for any snapshot configuration.
Although the routing tables are frozen, routing updates are still sent at their regular intervals out
of any LAN interfaces on the router. For example, if there is an Ethernet segment on the
opposite side of a snapshot router, the routing updates still broadcast out of that interface at the
normal update interval, while remaining dormant on the BRI interface. It is possible to force
the quiet period to expire and start the active period manually using the clear snapshot quiet-
time command. To monitor snapshot routing processes, use the show snapshot command.
Primary Rate Interface
PRI implementations are based on T1/E1 technologies. Although PRI is still ISDN, it is treated
differently in regard to framing and signaling. Like BRI, PRI has only one connection to the
ISDN network, and the switch type must be specified for the configuration to function. An
ISDN PRI T1 implementation has 23 B channels and a D channel. As with BRI, each of the
B channels has 64-kbps bandwidth available. The D channel, however, is also a 64-kbps
channel (unlike BRI).
In traditional T1 implementations, 24 timeslots exist. Obviously, one of the 24 timeslots
(timeslot 23, counting 0­23) is taken way for signaling and framing. With E1 PRI
implementations, there are 30 B channels available and one D channel, all having 64-kbps
bandwidth available.
Example 6-27
RouterA Snapshot Routing Configuration Example
RouterA(config)#hostname RouterA
RouterA(config)#isdn switch-type basic-5ess
!
RouterA(config)#interface BRI0
RouterA(config-if)#snapshot server 5 dialer
RouterA(config-if)#dialer map snapshot 1 name RouterB 2145552222
Example 6-28
RouterB Routing Configuration Example
RouterB Snapshot Routing Configuration Example
RouterA(config)#hostname RouterB
RouterA(config)#isdn switch-type basic-5ess
!
RouterA(config)#interface BRI0
RouterA(config-if)#snapshot client 5 720 dialer
RouterA(config-if)#dialer map snapshot 1 name RouterA 2145551111