// Workers AI · dad joke modeWhat did Session Announcement Protocol say? "I'm announcing my presence.
The Session Announcement Protocol (SAP) is an experimental protocol for advertising multicast session information. SAP typically uses Session Description Protocol (SDP) as the format for Real-time Transport Protocol (RTP) session descriptions. Announcement data is sent using IP multicast and the User Datagram Protocol (UDP).
Under SAP, senders periodically transmit SDP descriptions to a well-known multicast address and port number (9875).[1] A listening application constructs a guide of all advertised multicast sessions.
Announcement interval
[edit source]The announcement interval is cooperatively modulated such that all SAP announcements in the multicast delivery scope, by default, consume 4000 bits per second. Regardless, the maximum announce interval is 300 seconds (5 minutes). Announcements automatically expire after 10 times the announcement interval or one hour, whichever is greater. Announcements may also be explicitly withdrawn by the original issuer.
Authentication, encryption and compression
[edit source]SAP features separate methods for authenticating and encrypting announcements. Use of encryption is not recommended. Authentication prevents unauthorized modification and other DoS attacks. Authentication is optional. Two authentication schemes are supported:
- Pretty Good Privacy as defined in RFC 2440
- Cryptographic Message Syntax as defined in RFC 5652
The message body may optionally be compressed using the zlib format as defined in RFC 1950.
Applications and implementations
[edit source]VLC media player monitors SAP announcements and presents the user a list of available streams.[3]
SAP is one of the optional discovery and connection management techniques described in the AES67 audio-over-Ethernet interoperability standard.[4]
References
[edit source]- ↑ "SAP (v1 & v2): Session Announcement Protocol". Retrieved 2012-04-06.
{{cite web}}: CS1 maint: deprecated archival service (link) - ↑ M. Handley; C. Perkins; E. Whelan (October 2000). Session Announcement Protocol. IETF. RFC 2974.
- ↑ Viewing with Session Announcement Protocol (SAP), retrieved 2019-03-02
- ↑ "AES67-2013: AES standard for audio applications of networks - High-performance streaming audio-over-IP interoperability". Audio Engineering Society. 2013-09-11. Retrieved 2014-02-11.