The SDP Rewriter system feature rewrites session descriptions in messages forwarded between certain legs, to avoid SDP conflicts.


Feature script name


Applicable contexts

SIP service

SAS Support


Prerequisite features


Feature execution points

All post execution points


When a feature requires SDP conflict management, it can call SdpRewriting.startSdpRewritingForLegs() to start an SDP rewriting association between a pair of legs. This association is persisted in session state, and includes rules for rewriting SDP sent in either direction, so that conflicts are avoided. The SDP Rewriter feature then examines SDP message bodies on all messages sent on these legs, and rewrites the SDP as appropriate. If either party updates their session description, this feature updates its rewriting rules for the legs, so that changes are propagated correctly to the other party.

For more details see SDP conflict management.


The SDP Rewriter feature must run as a post-system feature on all execution points, to ensure that messages containing SDP sent by other features can be rewritten before transmission.

The feature must run before the SDP Monitor feature, so that SDP Monitor sees the updated SDP, if present.

Session state inputs and outputs


Name Type Format Description


A map containing Leg associations and SDP rewriting rules, created by SdpRewriting.

Updated when the feature detects a change in the session description, such as a new media line. The rewriting rules are updated so that SDP is rewritten correctly in both directions.




This feature is not configurable.


Statistic What it counts


The number of times that an SDP message body has been rewritten.

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Sentinel Express Version 4.1