I am running a single site deployment with CUCM ver 8.0(2) Pub/Sub. We have all phones in one Voice VLAN using three LAN switches and VTP to distribute the VLAN across the LAN. All phones are programmed with the same Device Pool. There is only one DateTime Group configured (CMLocal) at (GMT+9:00) Asia/Seoul*. I know the legacy phones require a time zone with the * if the firmware is prior to 9.0. Our phones are running SCCP43.9-03S. Our network is not running any NTP servers and all phones have a static IP address. Due to other issues, the CUCM Cluster has been re-installed and re-built with the same problem arrising: Some of the phones display the correct time while others are displaying GMT time.
Does anyone know the cause of this and how we can fix the issue?