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The messages related to circuit reservation are defined in this section.
Circuit Reservation Message: This message is used to perform continuity procedures on an outgoing SS7 circuit before collecting address digits from the incoming MF circuit. On receiving a seize from the incoming MF agency, a CRM with the required NOC is sent to the succeeding exchange and the timer TCRM (typically 15 seconds) is started. Based on the NOC, a continuity check may or may not be performed.
Circuit Reservation Acknowledgment: On receipt of a CRA message, the timer TCRM is stopped and further processing continues. If TCRM expires before the receipt of CRA, the CRM is re-attempted on a different CIC.
After sending a CRA in response to the CRM, a Timer TCRA (typically 15 seconds) is started by the terminating node while waiting for an IAM (or COT if a continuity check is to be performed). If neither of the messages is received and the timer expires, an REL message is sent from the terminating node with a cause value of "Temporary Call Flows.
Dual Seizure during CRM Processing
