IP Video Telephony Overview
IPv6 transition will follow Cisco Preferred Architecture deployment recommendations of IPv4. Cisco Unified Communications Manager (Unified CM) is the call control server for the Cisco Preferred Architecture for Enterprise Collaboration deployment. Cisco IP Phones, Cisco Jabber clients, and Cisco TelePresence video endpoints use SIP to register directly to Unified CM. The Unified CM cluster’s failover mechanism provides endpoint registration redundancy. If a WAN failure occurs and endpoints at remote locations cannot register to Unified CM, they use SRST functionality for local and PSTN calls, but some services such as voicemail and presence might not be available.