Question
Several messages did not get delivered, then all of them got delivered at the same time. Why?
Answer
This is most likely because of the store-and-forward methodology in which SMSC's handle the delivery of messages:
- The SMSC attempts to deliver the first message, but finds the receiving handset to be 'inactive' - i.e. it was 'off', out of coverage area or its memory was full. The SMSC then records this attempt and schedules a re-attempt after a brief waiting period.
- The SMSC then repeats this process again and again for the duration of the message's life (usually 3 days) with the addition of increasing the waiting time exponentially.
- If any messages are submitted to the same handset during the waiting period, the SMSC does not attempt to deliver them because it considers the handset to be inactive. It therefore creates a virtual queue for that handset and places any subsequent message in that queue. So, even though a phone may well be active, if it hasn't re-registered itself with the SMSC, the first message would block all other traffic from reaching it.
- When the handset re-registers itself with the SMSC, the first message is delivered and the path for the remaining messages is also opened. For this reason, all of them are delivered simultaneously.