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PA-A2 ATM CES Port Adapter Installation and Configuration
OL-3460-01
Chapter 1 Overview: PA-A2 ATM CES Port Adapter
Circuit Emulation Services Overview
source in distributing a single clocking signal throughout the chassis or to other network devices. This
clocking signal can be distributed wherever needed in the network to globally synchronize the flow of
CBR data. The use of this command is described in
Chapter 4, “Configuring the PA-A2 ATM CES
Port Adapter.”
Network Clock Distribution in a Cisco 7200 Series Router or a Cisco uBR7200 series
When equipped with an ATM CES port adapter and appropriate software, any Cisco 7200 series router
or a Cisco uBR7200 series can serve as a means for receiving and distributing a PRS to other devices in
the network.
A Cisco 7200 series router or a Cisco uBR7200 series can make use of a PRS that originates from any
one of several sources in the networking environment.
Figure 1-6
shows three possible sources of a PRS when two Cisco 7206 routers are connected
back-to-back. However, you should not interpret that to mean that only three such clocking signals can
be made available for use in the ATM network. In fact, more than three clocking signals may be present
in the Cisco 7200 series router or Cisco uBR7200 series operating environment.
The important concepts that you should take from
Figure 1-6
include the following:
•
Up to four clocking signals can be defined per Cisco 7200 series router or a Cisco uBR7200 series
in the network.
•
The PRS that is used in Cisco 7200 series routers or a Cisco uBR7200 series must be traceable to a
single clock source. (In
Figure 1-6
, Router No. 2’s PRS is traceable to Router No. 1’s PRS.)
Figure 1-6
Cisco 7206 Routers Connected Back-to-Back
Each PRS depicted in
Figure 1-6
is externally generated—that is, the timing signal originates from a
source outside the router. Also shown is an OC-3 trunk line that can propagate a PRS between adjacent
router/network devices.
If the Router No. 1 priority 1 PRS fails (CBR 4/0), the network clock synchronization service
automatically recovers network timing by using the Router No. 1 priority 2 PRS (CBR 4/3).
Assume, for example, that the T1/E1 line (CBR 4/0) at Router No. 1 in
Figure 1-6
is currently supplying
PRS to the network. If this PRS fails, the T1/E1 line (CBR 4/3) at the same router is used as PRS.
Router 2
Router 1
S5969
Cisco 7206
T1/E1 CBR 4/3
OC3/T3/E3
ATM 4/0
ATM WAN
uplink
OC3/T3/E3
ATM 2/0
T1/E1 CBR 4/2
T1/E1
CBR 2/2
T1/E1 CBR 4/1
T1/E1
CBR 2/1
T1/E1 CBR 4/0
T1/E1
CBR 2/3
T1/E1
CBR 2/0
PBX
PBX
PBX
PBX
Cisco 7206
PBX
PBX
PBX
PBX
PRS clock sources
1. CBR 4/0
2. CBR 4/3
PRS clock source
1. ATM 2/0
