Whenever an entity wishes to check the correctness of a call state at a peer entity, a STATUS ENQUIRY message may be sent requesting the call state. This may, in particular, apply to procedural error conditions described in 5.8.8 and 5.8.9.
Upon sending the STATUS ENQUIRY message,timer T322 shall be started in anticipation of receiving a STATUS message. While timer T322 is running, only one outstanding request for call state information shall exist. Therefore, if timer T322 is already running, it shall not be restarted. If a clearing message is received before timer T322 expires,timer T322 shall be stopped, and call clearing shall continue.
Upon receipt of a STATUS ENQUIRY message,the receiver shall respond with a STATUS message, reporting the current call state (the current state of an active call or a call in progress, or the Null state if the call reference does not relate to an active call or to a call in progress) and cause No. 30, response to STATUS ENQUIRY or No. 97,message type non-existent or not implemented (see 5.8.4). Receipt of the STATUS ENQUIRY message does not result in a state change.
The sending or receipt of the STATUS message in such a situation will not directly affect the call state of either the sender or receiver. The side having received the STATUS message shall inspect the Cause information element. If the STATUS message contains cause No.97, message type non-existent or not implemented, timer T322 shall continue to time for an explicit response to the STATUS ENQUIRY message. If a STATUS message is received that contains cause No. 30, response to status enquiry, timer T322 shall be stopped and the appropriate action taken, based on the information in that STATUS message, relative to the current state of the receiver. If timer T322 expires and a STATUS message with cause No. 97, message type non-existent or not implemented was received, the appropriate action shall be taken, based on the information in that STATUS message, relative to the current call state of the receiver.
These further appropriate actions are implementation dependent. However, the actions prescribed in the following subclause shall apply.
If timer T322 expires, and no STATUS message was received, the STATUS ENQUIRY message may be retransmitted one or more times until a response is received. The number of times the STATUS ENQUIRY message is retransmitted as an implementation dependent value. The call shall be cleared to the local interface with cause No. 41, temporary failure,if the STATUS ENQUIRY is retransmitted the maximum number of times. If appropriate, the network shall also clear the network connection, using cause No. 41, temporary failure.