A network node 104 maintains a database of session description protocol (SDP) precondition preferences for downstream network elements 106. On receiving a session initiation protocol (SIP) message comprising SDP preconditions, the network node 104 alters, adds or removes SDP preconditions according to the preferences or capability of the downstream network element 106. To maintain the database, the network node forwards an unmodified SIP message. If an error message or accept message is received from the downstream network element 106, the database is updated with the unsupported or supported preconditions. A second SIP message with modified SDP preconditions is then sent to the downstream node 106. The method reduces the number of error messages and retries leading to lower network traffic.
