title: SMS Gateway SMSC/ESME TON/NPI
body: <p>I'm developing an SMS Gateway and I was thinking about the features that I should implement in it. So I reviewed some SMS gateways (SMSNOW, SMS studio, and Ozeki) for examples.</p>
  
  <p>I almost finished the implementation but I came across a feature in almost all SMS gateways which allows the user to specify TON/NPI for SMSC and ESME.</p>
  
  <p>I understand that when the SMS gateway is preparing to send the sms using the SMPP protocol it would need to parse the sender/reciever number and based on that, specify TON/NPI. And I understand that it's great to allow you to override the defaults and specify your own TON/NPI.</p>
  
  <p>What I don't understand is why all SMS gateways give you the option to specify your own TON/NPI for the SMS gateway when it acts as SMSC (when it receives SMS, not sending them).</p>
  
  <p>What would the SMS gateway do with the specified TON/NPI when it recieves an smpp SMS?</p>