What happens when a SMS is sent to a receiver whose mobile phone is switched off? Where does sms go?

Where does the SMS go?

What happens when a SMS is sent to a receiver whose mobile phone is switched off? Where does it go?

The SMS sent from the mobile takes a route through the callers Service Provider network to his SMSC (SMS Centre) which is nothing but a server and then to the called mobiles’ Service Provider Network and to the called mobile number if it is in a switched on condition that is, in the normal course.

But before sending the message the status of the called number is first found out from the HLR (home location register) of the terminating network. A flag will be set in the HLR if the called mobile is switched off.

Hence the SMSC will not send the message but leave an indication to HLR to call back to receive the message as soon as the mobile is switched on. Till then the SMS is stored in the originating network’s SMSC.

Duration for storing depends on the design, may be for 4 hours or 6 hours or 2 days. HLR in the terminating network is monitoring the status of all mobiles continuously and immediately after sensing a ‘switched on’ condition of the called number.

HLR informs SMSC accordingly and the SMS is sent to called mobile number now.