receiving SMS messages

[Robert William Hutton]

Dan Weatherill wrote:
> If the phone is in standby, and I receive a text message, the phone 
> wakes up but does not receive a text message. The person sending the 
> message does, however, receive a delivery report. This occurs in both 
> images as well.
> 
> If I then subsequently receive a message after the others, whilst the 
> phone is out of standby, I receive all the messages together. Hence, no 
> messages are "lost" in the ether, but it seems that messages received 
> whilst the phone is on standby are temporarily mislaid.

This could be a possible explanation of what's going on:

1. The network attempts to send an SMS to your phone.
2. The GSM chip receives notification from the network that there's an SMS.
3. The GSM chip says to the network: wait, I'm temporarily unable to 
receive (as the phone's asleep) and wakes up the system.
4. The system comes up and waits.
5. In the meantime the network has accepted that the SMS can't be sent, 
and puts it into some kind of wait queue.

It's up to the network what kind of exponential backoff algorithm they 
use to decide when to resend.  If the phone goes back to sleep before 
the network attempts a resend, then the same events will occur at some 
later time and the SMS will end up going back into the queue.  Again and 
again.

On the Optus network, and from my experience with my old phone whose 
inbox filled up all the time, the time between retries can become long 
quite fast.  When a subsequent SMS is sent, this always flushes the 
retry queue as well, which is why you receive several messages at a time.

Cheers,

Rob.