session announcement protocol (IP) (SAP)
The Session Announcement Protocol(SAP) is a protocol developed by the Internet Engineering Task Force( IETF) for announcing web conferences used by clients with session directories. It is described in RFC 2974.
The SAP protocol works with a session directory that is updated by periodically polling all sessions.
For this purpose, the SAP protocol sends data packets to known multicast addresses and ports. The purpose of announcing the sessions is to ensure that the recipient of the message, who may also be a potential participant in an online meeting, is informed about the details of the session, such as the time in which the session is taking place, the call numbers of the other participants, or any media-related actions. This information is described in the Session Description Protocol( SDP) and transmitted in the payload of the SAP protocol.
Structure of the SAP header
The SAP header consists of several status bits and data fields. Several status fields are activated at the beginning of the header. These include the 3-bitversion field (V) and the one-bit Address Type data field (A), which indicates whether the data source is using IPv4 (0) or IPv6 (1). This is followed by several 1-bit fields, such as the Reserved field (R), which SAP users set to "0", this is followed by the Message Type data field (T), which identifies Session Announcement Packets (0) and Session Detection Packets (1). This is followed by the Encryption Bit (E), which indicates whether the payload is encrypted or not, and the Compressed Bit (C), which indicates whether the payload is compressed.
Behind these status indicators is the 8-bit Authentication Length data field, which indicates the number of 32-bit words in the Authentication Data data field. The Message Identifier Hash, a 2 byte long data field is used in conjunction with the Originating Source, the data source, for a globally unique occurring identification. The Originating Source data field contains the IP address of the data source.
The Timeout data field serves its purpose when the user data is encrypted. Since the time information within the payload data is also encrypted and cannot be read, an additional timestamp is inserted in the Timeout. The Payload Type follows, in which the format of the user data is described. This data field has a variable length. This is followed by the user data.