Chapter 2 Provisioning
Solution Architecture
Solution Architecture
Open Packet Telephony Overview
As an introduction to the Cisco VoIP: Infrastructure Manager Solution’s provisioning component applications and devices, the following overview of the emerging technology of distributed packet telephony is presented.
Telephony is no longer solely the domain of Public Switched Telephone Networks (PSTNs). Software and protocols that allow telephone calls over packet networks, such as the Internet, have entered the market place. They are based on:
•the Media Gateway Control Protocol (MGCP) and related protocols such as the Simple Gateway Control Protocol (SGCP) and Megaco/H.248
•the Session Initiation Protocol (SIP)
•H.323.
This discussion focuses on MGCP and H.323, which are both supported by the Cisco Packet Telephony Center and the entire provisioning suite of applications in the Internet OSS for packet based voice networks.
Examples of Open Packet Telephony Networks
Figure 2-1 depicts an example of an MGCP-based OPT network. (In this discussion, there is no need to distinguish further between the different MGCP derivatives, Megaco, H.248, and SGCP.) The bearer plane is responsible for the transport of the actual payload. Network elements within the bearer plane need not be concerned with the specifics of telephony applications. Switches or routers between media gateways at the edge of the OPT network provide for the actual bearer fabric (the data cloud), shuffling data packets back and forth. The control plane is responsible for signaling processing and call control; it is here that the actual call-processing intelligence resides. The components in the control plane are commonly referred to as Media Gateway Controllers (MGCs). MGCs control media gateways by instructing them when to set up or tear down connections, requesting notification of specific events for further processing, and so on. They contain all the logic required for telephony applications, including Signaling System 7 (SS7) signaling termination, collection of accounting information, and, very importantly, directory functions and call-level routing based on dial plans. In terms of numbers of devices, there tend to be much fewer MGCs than media gateways, meaning that call intelligence is fairly centralized.
Cisco Internet OSS for VoIP: Infrastructure Manager Implementation Guide
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