The B2BUA feature provides back-to-back user agent functionality to Sentinel.

Establishment to termination

The B2BUA feature divides the communication channel into two legs and mediates all SIP signaling between both ends of the session, from establishment to termination:

  • On an initial incoming SIP request, the feature creates an outgoing leg and links it to the triggering leg.

  • On all incoming SIP messages, if the triggering leg is linked, the feature adds an outgoing SIP message to the linked leg’s message queue, and sends it after the feature scripts have completed.

  • If configured to do so, on an incoming successful final response to an initial INVITE on the leg, the feature will send an early ACK, and will subsequently not B2BUA the ACK received from the linked leg. An early ACK will not be sent if there hasn’t been a completed SDP negotiation (offer & answer).

Note

This feature is a critical system feature, many features rely on the functionality and success of this feature, including the B2BUA SCUR, B2BUA ECUR and B2BUA IEC, and SDP Comparison features.

See Sentinel SIP Feature Execution Points for more about running critical features.

Details

Feature script name

B2BUA

Applicable contexts

SIP service

Prerequisite features

none

Feature execution points
Pre

SipAccess_SessionAccept SipAccess_PartyRequest SipAccess_PartyResponse SipMidSession_PartyRequest SipMidSession_PartyResponse SubscriptionAccept SubscriptionSipRequest SubscriptionSipResponse SipTransaction_Accept SipTransaction_Request SipTransaction_Response

Post

none

Session state inputs and outputs

Inputs

Name Type Format Description Behaviour if null/invalid

SentinelSelectionKey

com.opencloud.sentinel.common.SentinelSelectionKey

selection key

for example: <platform>::::

For selecting configuration data

Increment InputParameterErrors Common cleanup actions

Feature responses

Response Reason

featureHasFinished

Feature has finished.

featureFailedToExecute

Feature encountered a fatal error and was unable to continue.

featureIssuedWarning

Feature encountered a non-fatal error during execution.

B2BUA configuration

The configuration for the B2BUA feature is provisioned in the following table:

Parameter Type Description

PreserveCallIdOverB2BUA

Boolean

If true, the outgoing dialog will use the same SIP Call-ID as the incoming dialog.

SendEarlyInitialInviteACK

Boolean

If true, on receiving a 2xx Response to an Initial INVITE request, an ACK will be sent on the dialog, and the incoming ACK will not be sent on the linked leg.

Statistics

Statistic When incremented

FailedToCreateOutgoingLeg

The feature encounters an error while attempting to create the outgoing leg.

FailedToCreateOutgoingMessage

The feature encounters an error while attempting to create an outgoing request on a newly created leg.

FailedToForwardMessage

The feature encounters an error while attempting to forward a message across the B2BUA.

FailedToLinkLegs

The feature encounters an error while attempting to link a newly created outgoing leg to the original incoming leg.

Started

The feature is invoked.

FailedToStart

The feature fails to start.

IssuedWarning

The feature encounters a non-fatal error and alerts the core.

FailedDuringExecution

The feature encounters any fatal error and alerts that core.

TimedOut

The feature fails to complete execution within the allowable time frame.

Provisioning interfaces

The feature is provisioned using the Sentinel Features REST API or web interface.

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Sentinel Express Version 2.7.0