Cisco expert help is required

Cisco expert help is required

SRST stands for Survivable Remote Side Telephony. It’s a topic of centralized call processing in which you can have multiple physical sites but all of your IP phones are registered to one server kept at one physical location. By configuring SRST fallback, you can make IP phones on one location to be able to communicate with each other even if the connection to the server has been lost.

Cisco expert help is required

The letters “SRST” stands for “Survivable Remote Site Telephony.” It is a “CUCM” or “Cisco Unified Communications Manager” call processing backup mechanism that allows Cisco IP phones to register to a Cisco router. In SRST mode, a Cisco router provides call setup and call teardown services just like with a CUCM but only when connectivity to the CUCM servers provided in the Cisco Call Manager group are unreachable.

Cisco IP phones usually registers to CUCM whether you use Single Site Deployment, Multi-site with Centralized/Distributed Call Processing Model, or Clustering over IP WAN. In cases when there is WAN failure or the primary, secondary, or tertiary CUCM server goes down, the remote site end points won’t be able to reach Cisco Call Manager and the IP phone’s registration will be lost and call processing/call control will also not work.

In these events, the SRST or the Survivable Remote Site Telephony has the capability to provide call setup and call teardown services for the sites that don’t have a local CUCM server. It can provide basic telephony features to the endpoints and can perform PSTN and VoIP calls within the local site.

No calls will be routed over WAN because the WAN link is down or maybe the CUCMs are not accessible.