The B2BUA Subscription Activity Guard feature tracks outstanding subscriptions and invalidates sessions which have not been correctly shut down.

The B2BUA Subscription activity guard feature is used to protect against servers not correctly terminating their subscriptions. For each non-terminating notify that is B2BUAed by Sentinel, this feature starts a timer which fires after the expiration of the notify. If another notify for the same subscription is received, the timer is updated. If a terminating notify is sent, the timer is cleared and removed. If the timer fires, this shows that a terminating notify has not been sent by the server. In this case, the feature invalidates and detaches from both legs of the call, freeing resources and cleaning up as appropriate.


Feature script name


Applicable contexts

SIP service

SAS Support


Prerequisite features


Requisite Features execution point [script]

SubscriptionSipRequest [Pre]

Timer usage

Feature-targeted timer triggers feature directly on expiry. Does not need to be registered against SipAccess_ServiceTimer execution point.

Session state inputs and outputs


Name Type Format Description Behaviour if null/invalid



selection key
for example, <platform>::::

For selecting configuration data

Increment InputParameterErrors Common cleanup actions

Feature responses

Response Reason


feature has finished


Name Description


Number of times the timer fired and the feature had to terminate the subscription.

B2BUA Subscription Activity Guard configuration

The configuration for the B2BUA Subscription Activity Guard Feature is provisioned in the following table:

Parameter Type Description



Number of milliseconds to wait after the expiry time before shutting down the legs.

Provisioning interfaces

The feature is provisioned using the Sentinel web interface.

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Sentinel Express Version 4.1