Part 1: Basic SRST Configuration
Part 2: SRST Configuration: IP Phone Clock, Date, and Time Formats
Part 3: SRST Configuration: IP Phone Language Display
Part 4: SRST Configuration: IP Phone Customized System Messages
Part 5: SRST Configuration: Secondary Dial-Tone
Part 6: SRST Configuration: Dual and Octo Line Phones
In this post, I'm going to outline how to configure clock, date, and time formats used by IP phones registered to a gateway in SRST-mode. While this may seem like a trivial issue, I can assure you that an office gets quite annoyed when their phones do not reflect the methods of displaying the time and date that are locally popular. Furthermore, note the following very important distinction in how the newer 797x IP Phones handle this when compared with the older 7940/7960-style IP Phones.
Cisco Unified 7970G & 7971G IP Phones
The Cisco Unified IP Phone 7970G and Cisco Unified IP Phone 7971G-GE IP phones obtain the correct timezone from Cisco Unified Communications Manager. They also receive the Coordinated Universal Time (UTC) time from the SRST router during SRST registration. When in SRST mode, the phones take the timezone and the UTC time, and apply a timezone offset to produce the correct time display.
Cisco Unified 7940 & 7960 IP Phones
Cisco IP Phone 7960 IP phones and other similar SCCP phones such as the Cisco IP Phone 7940, get their display clock information from the local time of the SRST router during SRST registration. If the Cisco Unified SRST router is configured to use the Network Time Protocol (NTP) to automatically sync the Cisco Unified SRST router time from an NTP time server, only UTC time is delivered to the router. This is because the NTP server could be physically located anywhere in the world, in any timezone. As it is important to display the correct local time, use the clock timezone command to adjust or offset the Cisco Unified SRST router time.
Router(config)# clock timezone PST -8
Router(config-cm-fallback)# time-format 24
Router(config-cm-fallback)# date-format mm-dd-yy
Cisco Unified SRST System Administrator's Guide