SIP Early Media Suppression
This section explains how to configure SIP early media suppression, which lets you determine who can send early media and in what direction. Early media are the RTP/RTCP packets sent from the called party to the caller, or vice versa, before a session is fully established (before a 200 OK is received). When the Oracle® Enterprise Session Border Controller receives an INVITE message with SDP, it can forward media packets to the calling endpoint as soon as it forwards the INVITE to the next hop. It can also forward media packets received from the calling endpoint to the called endpoint as soon as the Oracle® Enterprise Session Border Controller receives SDP in a SIP response to the INVITE, usually a provisional message. This allows for any early media to be played, such as remote ringback or announcement.
Early media can be unidirectional or bidirectional, and can be generated by the caller, the callee, or both.
With early media suppression, you can block early media until the call is established. You can define which outbound realms or next hop session agents are allowed to send or receive early media. early media suppression only applies to RTP packets. RTCP packets received by Oracle® Enterprise Session Border Controller are still forwarded to their destination in both directions, unless an endpoint is behind a NAT and the media manager has not been enabled for RTCP forwarding.
Note:
To use early media suppression, you cannot configure media release of any kind: same-realm, same-network, or multiple-system media release.With the SIP-based addressing, early media suppression is based on the outbound SIP interface realms and the value of their early-media-allow parameter. When the Oracle® Enterprise Session Border Controller forwards a SIP Invite out a SIP interface, the outbound realm is chosen based on the SIP layer information, such as the session agent for the next-hop or the address prefix of the next-hop SIP device. The matching realm’s early-media-allow parameter value then applies to either allow all, block all, or block one-way early media until a 200 ok is received. At that point bidirectional media is allowed. The decision is based on SIP-layer addressing of next-hops.
You configure a rule for a realm or a session agent to use early media suppression. An early media suppression rule specifies whether you want to prevent early media in any direction, allow early media going to the calling endpoint in the reverse direction, or allow early media in both directions. The forward direction is when the packets flow from the caller to the called party. The reverse direction is when the packets flow from the called party to the caller.
The early media suppression rule is applied to a session. When the Oracle® Enterprise Session Border Controller initiates a new session, it first checks whether the next hop is a session agent and if so, whether an early media suppression rule has been configured it. If an early media suppression rule is found, the Oracle® Enterprise Session Border Controller enforces it. If the next hop is not a session agent or no early media suppression rule is configured, the Oracle® Enterprise Session Border Controller checks whether an early media suppression rule has been configured for the outbound realm. If it finds one, it enforces it.