SMS-MT Never Delivered When the Subscriber is Offline as per HLR Query. (Doc ID 1196674.1)

Last updated on NOVEMBER 13, 2023

Applies to:

Symptoms

Pre-requisites

In the situation where a Short Message Service - Mobile Terminated  (SMS-MT) must be delivered to a subscriber, the Short Message Service Center (SMSC) will query the Home Location Register (HLR) to retrieve the current status of the subscriber before delivering the message.  To do this, the SMSC invokes the Mobile Application Part (MAP) service package MAP_SEND_ROUTING_INFO_FOR_SM, which sends a sendRoutingInfoForSM (SRI-SM) MAP message to the destination number's HLR, requesting their present location. Hence, SMSC will discover the location of the B-Party in order to be able to correctly deliver the text to the recipient.

Here is the general figure of a Mobile Terminated Short Message delivery.

Context

In the context of SMS Home routing, the terminated message should be routed to the home network in order to apply value-added SMS services via the Intelligent Network (IN), i.e. Oracle Communications Network Charging and Control (OCNCC or NCC) application in our case.

In that situation, the IN will interact between the SMSC and the HLR to provide value-added services.

In other words, the SMSC will send the SRI-SM to OCNCC (Messaging Manager (MM) module on the Service Logic Controller (SLC)) and not directly to the HLR.  MM will then relay the SRI-SM to the HLR and handle responses back from HLR to SMSC.

The issue

In the case the subscriber is offline (e.g. his mobile phone is turned off), the flow to deliver the message would be:

Without IN interaction:

1. SMSC sends SRI-SM to HLR
2. HLR knows that the B-number is offline and responds with NACK and an informServiceCentre (informSC) operation (note: HLR records the Service Center (SC) address for future reference, in this case SMSC address)
3. When the B-number comes online again, HLR notifies the SMSC through an alertServiceCentre (alertSC) operation
4. SMSC delivers the message to B-number via a mt-ForwardSM operation

With IN interaction (current and incorrect flow):

1. SMSC sends SRI-SM to SLC (NCC MM module)
2. SLC sends SRI-SM to HLR
3. HLR knows that the B-number is offline and responds with NACK and an informServiceCentre (informSC) operation to the SLC/MM. (note: HLR records the SC address for future reference, in this case SLC/MM address)
4. SLC/MM relays the informSC to SMSC
   
5. When the B-number comes online again, HLR notifies the SLC/MM through an alertServiceCentre (alertSC) operation
6. SLC/MM relays the alertSC to the SMSC
7. SMSC sends mt-ForwardSM operation to the SLC/MM for delivery.

In the scope of this document, it has been noted that step 4 (optional) and most importantly step 6 fails.
In other words, the SMSC is never aware that the subscriber is online again. Therefore, customers are complaining that they don't receive SMS-MT or only after a very long time (SMSC retry-period).

Error messages

We are facing 2 different problems:

• The symptom for informSC not being delivered (step 4 above) is visible in Routing Information for Mobile Services (RIMS - this has been rebranded to Messaging Manager Navigator) module (i.e. sub-module, part of MM module, which is in charge of HLR interaction) log file:

• There is no error message for step 6, except that the MT message is not delivered.  It can be seen on SMSC that alertSC has not been received though.

Cause

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