Cisco SRST Configuration

SRST or Survivable remote site telephony is a High availability mechanism which provides Call Survivability to the phones & trunks at a remote office in an event of network isolation from their CUCM Subscribers/Call Agent Servers. Here are the steps that are required to configure SRST using call-manager-fallback method. We can also use CME as SRST which will see later. CME as SRST provides a much better feature functionality compared to call-manager-fallback.

Step 1: Configure SRST Reference on CUCM for the remote site.

Step 2: Assign the SRST Reference to the  Device Pool (DP) of the remote phones. You may also use the default gateway of the Voice VLAN. reset all the phones & verify that the phones show SRST router as their Call Agent after CUCM Servers under the Setting >> Device Configurations >> Unified CM Configurations.

Step 3:  Configure SRST call-manager-fallback on the Voice Router at the remote site. This will provide Call Agent functionality to the SCCP phones. You can configure SIP SRST too. This configuration is applicable only for SCCP Phones.

 call-manager-fallback

     ip source address 10.18.71.1             >> SRST Reference IP address
     max-ephones 40
     max-dn 100 octo-line
     system message primary FallBack Mode. CUCM Down.
     voicemail 4999
     call-forward busy 4999
     call-forward noan 4999 timeout 12
     time-zone 8
     time-format 24
     date-format mm-dd-yy

Step 4: [Optional] If you have the Gateways registered to CUCM using MGCP Protocol, then you must also configure MGCP fallback which basically provides the option to the gateway to use H323 or SIP in an event of network disconnection to the CUCM Subscribers.

ccm-manager fallback-mgcp <<< if its an MGCP Site.

Step 5: Configure your dial plan using Dial Peers to enable call routing. This may be minimal if you are using H323, but will require you to configure your all applicable routes in case you're using MGCP. Here is a sample minimal configuration.

dial-peer voice 1 pots
destination-pattern 9[2-9]......
port 2/0/0:23
forward-digits 7
!
dial-peer voice 2 pots
destination-pattern 91[2-9]..[2-9]......
port 2/0/0:23
forward-digits 11
!
dial-peer voice 3 pots
destination-pattern 9011T
port 2/0/0:23
prefix 011
!
dial-peer voice 10 pots
description Abbreviated Dialing to HQ Site
destination-pattern 4...
port 2/0/0:23
no digit-strip
prefix 1212902
!

Hope this helps. Good day.