I’ve had two folk tell me they received an SMS message from me today. One was sent 16th July and the other 26th July. As far as my phone knows they were both sent on the original dates.

So, where have they been hiding and why did they (both) put in an appearance today?

did you send them 2nd class?

It’s something to do with packet sending, I believe: how the message gets broken down and re-assembled to pass through the networks. I’ve sent a message to a friend before now that’s woken her up by her phone beeping at 3am, when I sent the message a day or so previous.

You haven’t replied to the one I sent you in 2010

did you restart your phone today? any messages which had previously failed to send will be sent. happens here on our two sony xperias

were you sacking them?

SMS server or gateway server could have been down, or if the people that received them had no coverage or the HLR ( Home Location Register ) hadn’t updated then it wouldn’t know where the phone is to send the message. Any number of possible issues unfortunately

SMS is a “store and forward” service, so the messages go to the SMSC which stores them, then it tries to deliver. If they don’t get through it’ll then go into a retry schedule. If the destination phone is restarted this should trigger a call to SMSC for any waiting messages.

It shouldn’t take days though, unless their phones have been off or out of coverage for that time. Undelivered messages also expire after a while – 30 days is the norm I think.

Sounds like they got stuck somewhere in the network. Probably down the back of the sofa in the server room.

Oh well no harm done – just a few billion electrons temporarily inconvenienced.