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Circuit Emulation Services Overview
Router No. 2 has ATM 2/0 as its PRS. If the ATM 2/0 port fails, there is no configured alternate clock
source for PRS. The default clock source is the local oscillator. But, in this case, this is not a problem
because the traffic from the T1/E1 CBR ports is also disrupted. In the Cisco 7200 series router or the
Cisco uBR7200 series, all T1/E1 traffic goes only on the ATM WAN uplink. When ATM 3/0 goes up,
the PRS is automatically recovered.
If the Router No. 1 priority 1 PRS is restored to service, the network clock synchronization service
automatically reverts to this PRS for timing purposes, regardless of which lower priority PRS may be
active at the time.
Figure 1-7
can be derived from the ATM network and provided to an edge node and propagated through the network
to synchronize the flow of CBR data between the communicating ATM end nodes.
In
Figure
edge of the network on T1/E1 trunk lines on the ATM CES port adapter in Routers 1, 2, and 3 are
synchronized.
Figure 1-7
PBX
PBX
Figure 1-8
transmit clocks, ATM CES T1/E1 transmit clocks, ATM CES OC-3/T3/E3 ATM WAN uplinks, and
ATM network OC-3/T3/E3 ATM port transmit clocks are all derived from and referenced to a single
clock source, the PRS. This limits the jitter and wander in the emulated circuits.
PA-A2 ATM CES Port Adapter Installation and Configuration
1-10
illustrates Cisco 7206 routers connected to an ATM network. This figure shows how a PRS
1-7, when the PRS clock source is taken from the ATM network, all the transmit nodes at the
Cisco 7206 Routers Connected to ATM Network
PBX
T1/E1
Cisco 7206
T1/E1
Router 1
T1/E1
PRS clock source
1. ATM WAN uplink
T1/E1
PBX
illustrates a typical configuration of a network clock source. In this figure, the PBX T1/E1
ATM WAN
uplink
ATM
network
OC3
ATM WAN
OC3
uplink
PRS clock source
Router 3
1. ATM WAN uplink
Chapter 1
Overview: PA-A2 ATM CES Port Adapter
Cisco 7206
ATM WAN
uplink
Router 2
T3/E3
PRS clock source
1. ATM WAN uplink
PBX
T1/E1
PBX
T1/E1
OL-3460-01
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