IETF RFC 5888 PDF

Introduction

RFC 3388 [RFC3388] specified a media-line grouping framework for SDP [RFC4566]. This specification obsoletes RFC 3388 [RFC3388].

An SDP [RFC4566] session description typically contains one or more media lines, which are commonly known as "m" lines. When a session description contains more than one "m" line, SDP does not provide any means to express a particular relationship between two or more of them. When an application receives an SDP session description with more than one "m" line, it is up to the application to determine what to do with them. SDP does not carry any information about grouping media streams.

While in some environments this information can be carried out of band, it is necessary to have a mechanism in SDP to express how different media streams within a session description relate to each other. The framework defined in this specification is such a mechanism.