ts.SIPT1

Specifies the T1 timer duration used by the internal SIP stack to determine the intervals between INVITE attempts sent by the Telephony Session service. This duration represents an estimate of the round trip time in milliseconds (ms) for messages between the Telephony Session service and Voice Browser service.

If the initial INVITE from the Telephony Session service to a Voice Browser service instance does not receive a response, the Telephony Session service repeats the attempt after this interval. If this second attempt is also ignored, the Telephony Session service doubles the interval and tries again. On subsequent attempts it continues to double the interval until the interval exceeds four seconds (the default T2 value).

The Telephony Session service issues INVITE attempts to the Voice Browser service instance for a total period equal to the ts.SIPT1 value times the ts.SIPTimerBMultiplier value (see ts.SIPTimerBMultiplier).

If the timeout occurs before an INVITE is accepted, the Telephony Session service marks the Voice Browser service instance as failed. It then ceases INVITE attempts to this instance, and sends OPTIONS polls at the specified ts.SIPFailedCheckTime interval until the instance is restored. The Telephony Session service then tries the other Voice Browser service instance.

If no Voice Browser service instance is available, the Telephony Session service returns a 480 Temporarily Unavailable message.

The default value is 200 ms, which (along with the ts.SIPTimerBMultiplier default of 30) allows the Telephony Session service to try both Voice Browser service instances before the remote party times out.

For more information on INVITE intervals and timeouts, see the SIP RFC 3261.