■ The Cisco Unified Communications System Architecture fully integrates communications by enabling data, voice, and video to be transmitted over a single network infrastructure using standards-based IP.
■ VoIP is the family of technologies that allows IP networks to be used for voice applications, such as telephony, voice instant messaging, and teleconferencing.
■ VoIP use H.323, MGCP, SIP, and SCCP call signaling and call control protocols.
■ Signaling protocol models include peer-to-peer and client/server categories of protocols.
■ Configuring voice in a data network requres network services with low delay, minimal jitter, and minimal packet loss.
■ The actual voice conversations are transported across the transmission media using RTP and other RTP-related protocols.
■ Gateways connect IP Communications networks to traditional telephony networks.
■ Several types of voice gateways meet all kinds of customer needs, from small enterprises to large service provider networks.
■ Supported Cisco IP telephony deployment models are single site, multisite with centralized call processing, multisite with distributed call processing, and clustering over the IP WAN.
■ In the sing-site deployment model, the Cisco UCM applications and the DSP resources are at the same physical locatioin. The PSTN handles all external call.
■ The multisite centralized model has a single call-processing agent. Applications and DSP resources are centralized or distributed, and the IP WAN carries voice traffic and call control signaling between sites.
■ The multisite distributed model has multiple independent sites, each with a call processing agent, and the IP WAN carries voice traffic between sites but not cal control signaling.
■ Clustering over an IP WAN provides central administration, a unified dial plan, feature extensioin to all offices, and support for more remote phones during failover, but places strict delay and bandwidth requirements on the WAN.