tailieunhanh - The Illustrated Network- P79

The Illustrated Network- P79:In this chapter, you will learn about the protocol stack used on the global public Internet and how these protocols have been evolving in today’s world. We’ll review some key basic defi nitions and see the network used to illustrate all of the examples in this book, as well as the packet content, the role that hosts and routers play on the network, and how graphic user and command line interfaces (GUI and CLI, respectively) both are used to interact with devices. | CHAPTER 30 Voice over Internet Protocol 749 RAS Call Status Control UDP TCP IP Data Link Physical Media Signaling Stack MGCP Megaco Signaling Stack FIGURE Three VoIP signaling architectures. the International Standard The signaling protocol framework is the international telephony standard for all telephony signaling over the packet network not just the Internet . When work on began the packet network most commonly mentioned for was then ATM and not the Internet. In a sense doesn t care it s just an umbrella term for what needs to be done. Like RTP was designed for audio and video conferencing not just point-to-point voice conversations. A LAN with devices that support capabilities terminals which have many different subtypes also has an multipoint control unit MCU for conference coordination. The LAN includes an gateway to send bits to other zones and an gatekeeper. The gatekeeper is optional and is needed only if the terminals are so underpowered they cannot generate or understand messages on their own. Most can although is not trivial. The gateway is essentially a router but with the ability to support packetized voice to PSTN connections and the terminals are computers of course . The main signaling protocols used with VoIP are RAS Registration Admission and Status which is used to register the VoIP device with the gatekeeper and CS call status which is used to track the progress of the call. The structure 750 PART VII Media FIGURE zone components. Optional components are shown in italic. of a typical zone is shown in Figure . signaling uses both UDP and TCP when run on an IP network and uses RTP and RTCP for transport. Components that are not strictly needed for VoIP are shown in italics. supports not only audio and video conferencing but also data conferencing where users can all