ABSTRACT

This section describes Request for Comments (RFCs) 5939, 6236, 6871, and 7006 that deal with how the session description protocol is used for negotiation of capabilities between conference participants for session establishment based on agreed-upon session, media, and transport attributes. First, we describe RFC 5939 that addresses the Session Description Protocol (SDP) offer/answer procedures providing a general SDP capability negotiation framework. It also specifies how to provide attributes and transport protocols as capabilities and then negotiate them using the framework. Extensions for other types of capabilities (e.g., media types and media formats) are provided throughout this book. Second, a new generic session setup attribute is described here (RFC 6236) to make it possible to negotiate different image attributes such as image size. A possible use case is to make it possible for a low-end handheld terminal to display video without the need to rescale the image, something that may consume large amounts of memory and processing power. This chapter also explains how to maintain an optimal bit rate for video as only the image size that is desired by the receiver is transmitted. Third, the capability negotiating framework has been extended further by defining media capabilities (RFC 6871) that can be used to negotiate media types and their associated parameters. Finally, we describe RFC 7006 that extends the SDP capability negotiation framework to allow endpoints to negotiate additional SDP capabilities, namely, bandwidth ("b=" line), connection data ("c=" line), and session or media titles ("i=" line for each session or media).