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Configuring the Session Announcement Protocol

Understanding SAP and SDP

Session announcements are handled by two protocols: the Session Announcement Protocol (SAP) and the Session Description Protocol (SDP). These two protocols display multicast session names and correlate the names with multicast traffic.

SDP is a session directory protocol that is used for multimedia sessions. It helps advertise multimedia conference sessions and communicates setup information to participants who want to join the session. SDP simply formats the session description. It does not incorporate a transport protocol. A client commonly uses SDP to announce a conference session by periodically multicasting an announcement packet to a well-known multicast address and port using SAP.

SAP is a session directory announcement protocol that SDP uses as its transport protocol.

For information about supported standards for SAP and SDP, see Supported IP Multicast Protocol Standards.

Configuring the Session Announcement Protocol

Before you begin:

  1. Determine whether the router is directly attached to any multicast sources. Receivers must be able to locate these sources.

  2. Determine whether the router is directly attached to any multicast group receivers. If receivers are present, IGMP is needed.

  3. Determine whether to configure multicast to use sparse, dense, or sparse-dense mode. Each mode has different configuration considerations.

  4. Determine the address of the RP if sparse or sparse-dense mode is used.

  5. Determine whether to locate the RP with the static configuration, BSR, or auto-RP method.

  6. Determine whether to configure multicast to use its own RPF routing table when configuring PIM in sparse, dense, or sparse-dense mode.

The SAP and SDP protocols associate multicast session names with multicast traffic addresses. Only SAP has configuration parameters that users can change. Enabling SAP allows the router to receive announcements about multimedia and other multicast sessions.

Junos OS supports the following SAP and SDP standards:

  • RFC 2327, SDP Session Description Protocol

  • RFC 2974, Session Announcement Protocol

To enable SAP and the receipt of session announcements, include the sap statement:

You can include this statement at the following hierarchy levels:

  • [edit protocols]

  • [edit logical-systems logical-system-name protocols]

By default, SAP listens to the address and port 224.2.127.254:9875 for session advertisements. To add other addresses or pairs of address and port, include one or more listen statements.

Sessions established by SDP, SAP's higher-layer protocol, time out after 60 minutes.

To monitor the operation, use the show sap listen command.

See Also