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The 3G IP Multimedia Subsystem (IMS): Merging the Internet and the Cellular Worlds, Third Edition by Gonzalo Camarillo, Miguel A. García-Martín

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Chapter 16

Media Transport

There are two types of media when it comes to media transport: media that tolerates a certain degree of packet loss and media that does not. Examples of the first type are audio and video and examples of the second type are web pages and instant messages. If a few of the packets transporting an audio stream get lost the recipient may notice a decrease in the quality of the sound, but will probably be able to understand anyway. On the other hand, an instant message under packet loss may change from “I will not come tomorrow” into “I will come tomorrow”.

The transport protocol for a particular media is chosen based on the type of media. Traditionally, TCP has been used to transport media reliably and UDP to transport media unreliably. Nevertheless, UDP is not suitable for transporting large amounts of data traffic because it lacks congestion control mechanisms (i.e., congestion control would need to be implemented at the application layer, but it is seldom implemented at all). To address this issue the IETF is developing the Datagram Congestion Control Protocol (DCCP).

16.1 Reliable Media Transport

There are two transport protocols that provide reliable delivery of user data: TCP and SCTP (Stream Control Transmission Protocol, specified in RFC 2960 [308]). TCP delivers a stream of bytes, while SCTP delivers messages.

TCP works best when the recipient of the data does not need to wait until all of the data have arrived in order to start processing them. ...

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