MT (Mobile Terminated) Call Failures Reported In Hlr

Asset ID:	1-72-2118513.1
Update Date:	2017-01-19
Keywords:

Solution Type Problem Resolution Sure

Solution 2118513.1 : MT (Mobile Terminated) Call Failures Reported In Hlr

Applies to:

Oracle Communications Subscriber Data Management (SDM) - Version SDM 9.1.3 and later
Tekelec

Symptoms

Customer made some configuration changes in the HPMN definitions of network resulting in MT call failures.

Changes

Customer made configuration changes in the HPMN definitions of network which made the HLR consider the modified IMSI range as belonging to HPLMN.

Cause

Misconfiguration in HLR HPLMN definitions leads to Routing on SSN+PC instead of Routing on GT for Calling party address which was rejected by VLR.Traces pointed towards change in sccp routing to route on SSN+PC instead of Global Title.

Cause of change in SCCP Routing:-

Feature RoutingOnSsn = Activated in hlr configuration. This means that the IntraPLMN routing is based on PC + SSN. Below are more details about this feature:-

1) If the CC+NDC of the VLR the subscriber is currently registered matches the HPLMN nodes of the subscriber, that means the sub (and the VLR) is within HPLMN. Therefore while sending PRN, HLR will use RI=SSN and the VLR should be able to send PRN response back (VLR knows HLR PC).
2) If the CC+NDC of the VLR the subscriber is currently registered doesn't match any HPLMN nodes of the subscriber, that means the VLR is outside of HPLMN (roaming). Therefore when sending PRN, HLR will still use RI=GT because the VLR doesn't know HLR PC.

Before configuration changes, HLR treated the PLMN as roaming PLMN as a result Routing Indicator set by HLR was Route on GT and calls were successful. After definition changes, HLR started treating the PLMN as HPLMN and as per feature condition no. 1 was triggered which changed the routing indicator to Route on SSN + DPC. As VLR was not configured to accept this, so it stopped responding, which led to call failures.

Solution

1. HLR is sending PRN but there is no response from VLR, which led to call failures. So, in this case suggested to make changes in VLR to accommodate Routing on PC+SSN in case of HPLMN.
2. Suggested to deactivate the feature RouteonSSN , in this case routing will always be based on GT even in case of HPLMN also.

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