ABSTRACT

This section describes Requests for Comments (RFCs) 5547 and 4583 that deal with application-specific extensions in Session Description Protocol (SDP). The multimedia applications that are used among conference participants have certain application- and media-level capabilities and features. These specific features need to be agreed upon between the conference participants. We have considered two applications, file (e.g., text, still images, animation, audio, and video) transfer and binary floor control application protocol, that have been standardized in the Internet Engineering Task Force (IETF). In this chapter, we describe a mechanism specified in RFC 5547 to negotiate the transfer of one or more files between two endpoints by using the SDP offer/answer model specified in RFC 3264. SDP is extended to describe the attributes of the files to be transferred. The offerer can describe either the files it wants to send or the files it would like to receive. The answerer can either accept or reject the offer separately for each individual file. The transfer of one or more files is initiated after a successful negotiation. The Message Session Relay Protocol (MSRP) is defined as the default mechanism to actually carry the files between the endpoints. The conventions on how to use MSRP for file transfer are also provided in this chapter. In addition, this chapter specifies SDP syntaxes defined in RFC 4583 for supporting Binary Floor Control Protocol (BFCP) streams in SDP descriptions. User agents using the offer/answer model to establish BFCP streams use this format in their offers and answers.