Praise for Fundamentals of WiMAX

7.2 Multimedia Session Management 233Although not by itself an end-to-end IP QoS mechanism, MPLS it does provide a goodinfrastructure over which IP QoS may be implemented. Both IntServ and DiffServ mechanismsmay be implemented on an MPLS infrastructure, though MPLS-DiffServ is a more commonchoice. MPLS, however, breaks the end-to-end principle of IP protocols and puts control in thehands of the network operator.7.2 Multimedia Session ManagementA session may loosely be defined as a set of meaningful communications between two or moreusers or devices over a limited time duration. In the context of multimedia communications, theterm session includes voice telephony, audio and video streaming, chat and instant messaging,interactive games, virtual reality sessions, and so on. A session may also have multiple connectionsassociated with it; for example, a video conference, in which the audio and video parts areseparate connections.Session management encompasses more than transfer of bits from a transmitter to a receiver.It includes support for locating and getting consent from the parties involved in the communication,negotiating the parameters and characteristics of the communication, modifying it midstreamas necessary, and terminating it. For traditional IP data applications, such as Web browsingand e-mail, session management is rather simple. For example, for a Web download, a DNS(domain name server) is used to identify the appropriate Web site, TCP is used to reliably transferthe content, and the application itself—hypertext transfer protocol (HTTP)—is used to providebasic session management. Session management follows a “one size fits all” policy, with everyonepretty much getting to view the same Web pages without being able to specify preferences inany meaningful way. 7 IP multimedia communications, however, need a more robust sessionmanagementscheme, primarily because of the need to support a large variety of applications andterminals. Such session management tasks as capabilities negotiation become very importantwhen different terminals support different encoding schemes, for example. Or say, if one partywants to listen to the audio while others receive both video and audio of a multicast stream.Clearly, there is a need for a session-control protocol to support multimedia services, includingtelephony using IP. The ITU standard H.323 was the protocol that traditionally served this purposein most IP telephony and multimedia systems. Recently, a much more simple and lightweightprotocol, called the session initiation protocol (SIP), has emerged as the leading contender for thistask, and it will likely become the standard session control protocol used in WiMAX networks. SIPhas already been chosen as the session control protocol for third generation (3G) cellular networks(see Sidebar 7.1). Also needed is a transport-layer protocol that meets the requirements of multimediacommunications. Real-time transport protocol (RTP) was designed for this purpose. SIP andRTP work well together to provide the session-control and media-transport functions required forIP multimedia sessions. We provide a brief overview of these two protocols.7. Strictly speaking, MIME types are used to tell the browser the type of information it receives. Buta browser couldn’t choose if it wanted a .gif or .jpg file, for instance.