Introduction This document describes how to configure Cisco Unified Survivable Remote Site Telephony (SRST) on Cisco Unified Communications Manager 10.x and on Cisco IOS routers to provide redundancy to Cisco IP Phones.
Survivable Remote Site Telephony (SRST) is a feature which ensures that IP phones can continue to function even if they are unable to communicate with CallManager. During a failure, Cisco IP phones register with the local SRST router, which provides call processing and control. If Cisco IP phones detect that CallManager has come back online, they can fail back to that CallManager after a configurable interval (connection monitor duration). Cisco IP phones do not fail back immediately to ensure that the CallManager in question is back online and stable.
In this below example, SRST is configured at the remote site to provide redundancy in the event of a failure of connectivity to CallManager at the central site.
1. Configuring SRST on IOS Gateway Configure Survivable Remote Site Telphony on a branch site router to support basic functions for SCCP Phones
1. Open a telnet session to the router Site (Branch site) and login using the password
>configure terminal call-manager-fallback ip source-address 10.1.3.1 port 2000 max-ephones 20 max-dn 40
!--Enter SRST configuration mode using call-manager-fallback command !--Enter the source IP address of router ip source-address 10.1.3.1 port 2000
2. Configure Branch site phones for SRST
Configure the Phones in the branch site to use SRST as the fallback service. To provide the phones with the IP address of the SRST device in CUCM use Device pools.
1. Navigate to the CUCM 10.x administration page. 2. From the menu, select System > SRST 3. Click Add New 4. On SRST configuration page, use BR1-SRST for the reference name ( Branch site Router) 5. Enter the IP Address, 10.1.3.1 (Remote Branch Site IP Address) 6. Click Save 7. On CUCM Administration page, from the menu, select System > Device Pool 8. Click Find 9. On the Find and list Device pool page, modify the SRST reference to use BR1-SRST 10. Click Save and Reset
Use the command show call-manager-fallback all to verify the status of the SRST feature.
On the Branch Route site, use the CLI command show call-manager-fallback all to verify the status of SRST.
Testing: In order to check the operation of SRST feature, you can prevent the IP Phones on the Remote site from communicating with the CUCM. In this case, IP Phones get register with the local SRST router which provides call processing and control. Once the Cisco IP Phones detect that the call manager has come back online, they can fall back to the call manager.
Some useful commands to verify the correct operation of SRST are as follows:
debug ephone register: This displays the Cisco IP phone registration process in operation.
debug ephone keepalive: This displays keepalive debugging for Cisco IP phones.
debug ephone state: This displays state debugging for Cisco IP phones.
debug ephone detail: This displays detailed debugging for Cisco IP phones.
debug ephone error: This debugs error conditions for Cisco IP phones.
debug ephone statistics: This debugs call statistics for Cisco IP phones.
debug ephone pak: This displays at a voice packet level (the contents of one in every 1024 packets are displayed).
debug ephone raw: This provides low-level protocol debugging for all SCCP messages.
show ephone: This shows the Cisco IP phones that have already registered.