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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

Test Calls

When blockingMode is enabled in a particular sipTrunkGroup, the SBC blocks all the normal calls in either one or both the directions based on the blocking mode enabled except the test calls. The Sip Trunk Group blocking functionality does not impact the SBC test call processing. The test call functionality is required for the maintenance blocking between interconnected operator's networks.

To configure a Test Call Number Profile, refer to the section Test Call Number Profile - CLI.

Identifying a Test Call

The test calls received at the SBC carries calling party category indication as Test Call. 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.


P-Asserted-Identity: <;cpc=test >

P-Asserted-Identity: <sip:user1;;user=phone>

The SBC identifies the call as test call by examining the cpc parameter received in the P-Asserted-Identity header field. Additionally, the SBC compares the received called number against the pre-configured test call numbers in the Test Call Number Profile and selects the PSX (either to send normal PSX or test PSX) for further routing. The SBC routes the test call based on the PSX response.

Configuring Block Direction of the SBC

To set the blocking direction under SIP Trunk Group, enter the following command:

% set addressContext <addressContext name> zone <zone name> sipTrunkGroup <SIPTG name> blockDirection <bothways | incoming | none | outgoing>