Setting Up the Network
Information About Setting Up the Network
64
Cisco Unified SCCP and SIP SRST System Administrator Guide
OL-13143-04
Information About Setting Up the Network
When the WAN link fails, the Cisco Unified IP Phones detect that they are no longer receiving keepalive
packets from Cisco Unified CM. The Cisco Unified IP Phones then register with the router. The Cisco
Unified SRST software is automatically activated and builds a local database of all Cisco Unified IP
Phones attached to it (up to its configured maximum). The IP phones are configured to query the router
as a backup call-processing source when the central Cisco Unified CM does not acknowledge keepalive
packets. The Cisco Unified SRST router now performs call setup and processing, call maintenance, and
call termination.
Cisco Unified Communications Manager uses DHCP to provide Cisco Unified IP Phones with the IP
address of Cisco Unified Communications Manager. In a remote branch office, DHCP service is
typically provided either by the SRST router itself or through the Cisco Unified SRST router using
DHCP relay. Configuring DHCP is one of two main tasks in setting up network communication. The
other task is configuring the Cisco Unified SRST router to receive messages from the Cisco IP phones
through the specified IP addresses. Keepalive intervals are also set at this time.
How to Set Up the Network
This section contains the following tasks:
•
Enabling IP Routing, page 64
(Required)
•
Enabling Cisco Unified SRST on an MGCP Gateway
(Required)
•
Configuring DHCP for Cisco Unified SRST Phones, page 70
(Required)
•
Specifying Keepalive Intervals, page 73
(Optional)
Enabling IP Routing
To initiate SRST service, you need to enable IP routing command and configure an interface that you
want to use or bind. For information about enabling IP routing, see
Configuring IP Addressing
.
Enabling Cisco Unified SRST on an MGCP Gateway
To use SRST as your fallback mode with an MGCP gateway, SRST and MGCP fallback must both be
configured on the same gateway. The configuration below allows SRST to assume control over the voice
port and over call processing on the MGCP gateway. Due to command changes that were made in
Cisco IOS Release 12.3(14)T, use the configuration task that corresponds with the Cisco IOS Release
you have installed.
Note
The commands described in the configuration below are ineffective unless both commands are
configured. For instance, your configuration will not work if you only configure the
ccm-manager
fallback-mgcp
command.
