Cisco's IPT architecture divides voice system architectures into four major functional areas, as shown in Figure 15-10:
■ Client endpoints
■ Call processing
■ Service applications
■ Voice Enabled Infrastructure
Client endpoints include the IP phones, analog and digital gateways, and digital signal processor (DSP) farms. Included here is Cisco's IP Communicator, which is the software-based IP phone that runs on a PC or laptop. Gateways are used to access PBXs, analog phones, other IP telephony deployments, or the PSTN.
The Cisco Unified CallManager (CM) fulfills the role of call processing. The CM servers are the "brains" of the voice dial plan and are used to establish IPT calls between IP phones.
Figure 15-9 Converged VoIP Network
Voice Enabled Infrastructure
Service applications include IVR, Auto Attendant, and Unity Unified Messaging System for voice mail. Cisco IP Contact Center (IPCC) is used for enterprise call center applications. In addition, a standards-based Telephony Application Programming Interface (TAPI) allows third-party companies to develop applications for the Cisco Unified CallManager.
The voice-enabled infrastructure includes QoS-enabled devices such as LAN switches and routers. These devices are configured to be IPT-aware and provide service guarantees to the VoIP traffic. For example, LAN switches are configured with voice VLANs and Power over Ethernet (PoE) to service the IP phones. Also, WAN routers are configured with queuing techniques to prioritize VoIP streams over other traffic types.
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