Cisco CP-7911G-CH1 System Administrator Manual page 20

Cisco Unified SIP SRST
Table 2 Restrictions from Cisco SIP SRST from the Present Version to Version 3.0
Cisco Unified SRST Cisco IOS
Version Release
Version 8.0 15.1(1)T
Cisco Unified SCCP and SIP SRST System Administrator Guide
20
Restrictions
SIP phones may be configured on the Cisco Unified CM with an Authenticated
•
device security mode. The Cisco Unified CM ensures integrity and authentication
for the phone using a TLS connection with NULL-SHA cipher for signaling. If
such an Authenticated SIP phone fails over to the Cisco Unified SRST device, and
if the Cisco Unified CM and SRST device are configured to support secure SIP
SRST, it will register using TCP instead of TLS/TCP, thus disabling the
Authenticated mode until the phone fails back to the Cisco Unified CM.
Cisco Unified SCCP and SIP SRST Feature Overview
OL-13143-04