Session Announcement Protocol (RFC2974)
Original Publication Date: 2000-Oct-01
Included in the Prior Art Database: 2019-Feb-12
Internet Society Requests For Comment (RFCs)
M. Handley: AUTHOR [+2]
This document describes version 2 of the multicast session directory announcement protocol, Session Announcement Protocol (SAP), and the related issues affecting security and scalability that should be taken into account by implementors. This memo defines an Experimental Protocol for the Internet community.
Network Working Group M. Handley Request for Comments: 2974 ACIRI Category: Experimental C. Perkins USC/ISI E. Whelan UCL October 2000
Session Announcement Protocol
Status of this Memo
This memo defines an Experimental Protocol for the Internet community. It does not specify an Internet standard of any kind. Discussion and suggestions for improvement are requested. Distribution of this memo is unlimited.
Copyright (C) The Internet Society (2000). All Rights Reserved.
This document describes version 2 of the multicast session directory announcement protocol, Session Announcement Protocol (SAP), and the related issues affecting security and scalability that should be taken into account by implementors.
In order to assist the advertisement of multicast multimedia conferences and other multicast sessions, and to communicate the relevant session setup information to prospective participants, a distributed session directory may be used. An instance of such a session directory periodically multicasts packets containing a description of the session, and these advertisements are received by other session directories such that potential remote participants can use the session description to start the tools required to participate in the session.
This memo describes the issues involved in the multicast announcement of session description information and defines an announcement protocol to be used. Sessions are described using the session description protocol which is described in a companion memo .
Handley, et al. Experimental [Page 1]
RFC 2974 Session Announcement Protocol October 2000
A SAP announcer periodically multicasts an announcement packet to a well known multicast address and port. The announcement is multicast with the same scope as the session it is announcing, ensuring that the recipients of the announcement are within the scope of the session the announcement describes (bandwidth and other such constraints permitting). This is also important for the scalability of the protocol, as it keeps local session announcements local.
A SAP listener learns of the multicast scopes it is within (for example, using the Multicast-Scope Zone Announcement Protocol ) and listens on the well known SAP address and port for those scopes. In this manner, it will eventually learn of all the sessions being announced, allowing those sessions to be joined.
The key words ‘MUST’, ‘MUST NOT’, ‘REQUIRED’, ‘SHALL’, ‘SHALL NOT’, ‘SHOULD’, ‘SHOULD NOT’, ‘RECOMMENDED’, ‘MAY’, and ‘OPTIONAL’ in this document are to be interpreted as described in .
3 Session Announcement
As noted previously, a SAP announcer periodically sends an announcement packet to a well known multicast address and port. There is no rendezvous mechanism - the SAP announcer is not aware of the presence or absence of any SAP listeners - and no additional reliability is provided over the standard best-effort UDP/IP semantics.