Between HLR and GMSC (or SMSc).

SMSc can send an SRI-for-SM, and if the subscriber is absent, the response can include the informServiceCenter message, which lets the SMSc know if it will get sent an alertServiceCentre message when the subscriber comes back online (sends an UpdateLocation).

This means that the SMSc can be notified when it can deliver the message to the subscriber.

It’s got a bunch of flags, which equate to:

sc-AddressNotIncluded means the service center address from the SRI-for-SM was not included in the Message Waiting Data file (and therefore will not get notified via AlertSC when the subscriber comes back online).

If it’s sc-AddressNotIncluded is set to False it means that the service center address has been added to the Message Waiting Data file, so will get an alertServiceCenter message when the sub comes back online (Double negative).

mnrf-Set means Mobile subscriber Not Reachable (Not registered on any MSC)

mcef-Set means Memory Capacity Exceeded Flag is set as the HLR has run out of memory in the Message Waiting Data file and cannot store any more data (So you won’t get notified via AlertSC when the subscriber comes back online)

mnrg-Set is for Mobile subscriber Not Reachable for GPRS (When using SGSN delivery is not registered for packet service).

mnr5g-Set means the SC will get notified when the subscriber becomes reachable from 5G serving nodes.

mnr5gn3g is a mystery – The only references to it I can find are in the ASN1 spec (hence why Wireshark decodes it) but as to its purpose, I can only guess.