Specifications

Chapter 8 Configuring Survivable Remote Site Telephony
Overview of Survivable Remote Site Telephony
8-2
Catalyst 4224 Access Gateway Switch Software Configuration Guide
OL-2031-02
Overview of Survivable Remote Site Telephony
Cisco CallManager Releases 3.0 and later support Cisco IP Phones across the
WAN that are attached to a branch office Catalyst 4224. Without the SRST
feature, when the WAN connection between the branch office Catalyst 4224 and
Cisco CallManager fails or when connectivity with Cisco CallManager is lost, the
Cisco IP Phones at the remote site are unusable for the duration of the failure.
The SRST feature overcomes this problem, enabling the basic features of the
Cisco IP Phones by providing call-handling support on the Catalyst 4224 for its
attached Cisco IP Phones. The system automatically detects the failure and uses
the Simple Network Auto Provisioning (SNAP) technology to autoconfigure the
Catalyst 4224 to provide call processing for the local Cisco IP Phones.
When the WAN link or connection to the primary Cisco CallManager is restored,
call-handling capabilities for the Cisco IP Phones switch back to the primary
Cisco CallManager. During a failure when the SRST feature is enabled, the
Cisco IP Phone displays a message stating that the Cisco IP Phones are in the
Cisco CallManager fallback mode and are able to perform limited functions.
Note The Cisco IP Phone 7960 and 7940 displays the message “CM Fallback Service
Operating.” The Cisco IP Phone 7910 displays the message “CM Fallback
Service.”
Restrictions
Restrictions on the SRST feature are as follows:
• Supports only the Cisco IP Phone 7960, Cisco IP Phone 7940, and
Cisco IP Phone 7910 models
Note First-generation Cisco IP Phones, such as Cisco IP Phone 30 VIP and
Cisco IP Phone 12 SP+ are not supported.
• Does not support other Cisco CallManager applications or services such as
Cisco IP SoftPhone, Cisco Unity, or Cisco IP Contact Center
• Supports 24 Cisco IP Phones on the Catalyst 4224