R2511-HP MSR Router Series Voice Configuration Guide(V5)

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Configuring call watch
The call watch function is only applicable to voice E1/T1 interfaces. The E1/T1 interfaces mentioned in
this document are all voice interfaces.
Overview
Call watch enables a voice device to decide whether an E1/T1 interface is available for setting up calls
for a callee by monitoring the state of the local interface or the IP connectivity to the remote interface
connected to the callee.
Figure 85 Network diagram
As shown in Figure 85, a call watch-enabled voice device is connected through a local link to user B and
through an E1 or T1 link to the PBX to which user A is attached. This provides VoIP communication
between the two users in normal cases. When the local link is detected as unavailable, the voice device
sets the E1/T1 interface to watch-out state, disabling the interface to respond to calls from the PBX.
Detecting that the E1/T1 link is unavailable, the PBX switches to the backup link to forward calls from
user A to user B. When the local link recovers, the watch-out state of the E1/T1 interface is removed and
the PBX can thus dial through the E1/T1 link. As a result, calls from user A to user B are set up across the
local link.
Call watch concepts
Call watch group
The call watch function is implemented through call watch groups, each monitoring the state of one or
multiple local links.
Monitoring rule
A call watch group is a set of monitoring rules each defining a local interface or remote IP address
monitored by the group.
E1/T1
VoIP network
Backup
network
User B
User A
PBX
Voice device
Local link
Backup link