What “Absent Subscriber for SMS” Means

In GSM/SS7 networks, when an SMSC (Short Message Service Center) tries to deliver an SMS, it queries the HLR (Home Location Register) for routing information.
If the subscriber is not currently reachable—for example:

  • The handset is switched off,

  • The subscriber is outside coverage,

  • The IMSI is not registered in any VLR,

Then the HLR returns an “Absent Subscriber” error (MAP error code: absentSubscriberSM or AbsentSubscriber_SM).

⚙️ Typical Handling

  • The SMSC stores the message temporarily.

  • When the subscriber becomes reachable again (e.g., phone turns on, location update occurs), the HLR sends a Ready-for-SM (SRI-SM) notification to the SMSC.

  • The SMSC retries delivery automatically.

Common Causes

CauseDescription
Phone off / out of coverageDevice not registered in VLR
Roaming without SMS roaming supportNo route to SMSC
SIM inactive / suspendedHLR doesn’t return routing
Network configuration issueHLR/VLR mismatch or timeout