Internet Communications Using SIP : Delivering VoIP and Multimedia Services With Session Initiation Protocol {2Nd Ed.}

Transcoding Services

Transcoding services are provided by a human or machine acting as a third

party to replace one media set with another. A media set can consist of voice,

video, and text, depending on the impairments and preferences of the users.

Relay services are a subset of transcoding. Text relay services support the

transcoding between voice and interactive text, and are widely deployed on

the PSTN. By contrast, video relay services support the transcoding between

voice and sign language and are deployed on the Internet.

Transcoding Scenarios

A large variety of transcoding scenarios are possible using the Internet due to

the various multimedia possibilities and the capabilities of SIP for setting up

point-to-point and multipoint communication sessions. This has been well

documented based on significant early implementations of commercial ser-

vices and research projects reported in RFC 3351 [1]. One such scenario is

shown in Figure 17.5 as an example.

Figure 17.5 Examples for a transcoding scenario (a) network-based and (b) endpoint-

based.

Voice to Avatar Commands

Voice

Voice

XML Data

Deaf User

Deaf User

Hearing User

Hearing User

Text

Text to Voice

Voice

Voice

a. Transcoding service

b. Transcoding application in PC

294 Chapter 17