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IP Trunk Group Blocking Support

The blocking function restricts the SBC from sending a SIP request (outside an existing dialog) from its own network to the opposite network, but does not restrict receiving a SIP request (outside an existing dialog) from the opposite network to its own network.

When implementing a function that sends a test call, the network can send a test call to the opposite network even if blocking is enabled. The SBC allows all test calls even if blocking is enabled on trunk groups.

 When the Trunk Group is blocked in...Then the SBC does not allow out-of-dialog SIP requests that are... 
IncomingInbound to the Trunk Group
OutgoingOutbound to the Trunk Group
BothwaysInbound or Outbound to the Trunk Group
The following image depicts the blocking architecture:

Figure : Blocking Overview

The blocking functionality used in the maintenance system is achieved in the SBC with the pre-blocking and blocking functions:

Pre-blocking Function

The pre-blocking function restricts the sending out of a SIP request outside an existing dialog from its own network to the opposite network based on the IP addresses belonging to the opposite network. Established sessions are not restricted. The operator responsible for maintenance can confirm or are notified that all sessions are terminated.

Blocking Function

The blocking function prevents SIP requests from being sent outside an existing dialog from the originating network to the opposite network. The blocking function does not restrict the originating network from receiving a SIP request outside an existing dialog from the opposite network.

Test Call Support

The test call functionality is required for maintenance blocking between interconnected operator's networks. When the calling party's category is applied to indicate that the call is "test call," a cpc parameter with the value test is inserted in the P-Asserted-Identity header field of the initial INVITE request. When SBC sees cpc=test in the PAI header field, the call will be treated as test call.

The test calls can be received even when the Trunk Group is disabled or in out-of-service.