Mobile Number Portability (MNP): Behind the scenes

Mobile Number Portability allows swithcing between mobile phone operators without changing the mobile number. Sounds simple, but there are loads of tasks performed behind the scene at the operator end.

Few terms used:

• SIM (Subscriber Identity Module):
  • Securely stores IMSI number used to identify a mobile device.
• IMSI (International mobile subscriber Identity):
  • A 14-digit number that uniquely identifies for your sim card in entire world. It is used for routing calls to the user.
• MSISDN (Mobile Subscriber Integrated Services Digital Network):
  • Identifies the SIM card inserted in to the mobile phone
  • MSISDN is mapped against the IMSI and the map is known by the SIM issuing network operator.
• ICC-ID (Integrated Circuit Card ID):
  • Every SIM is internationally identified by an unique ICC-ID. It is a 19-digit number printed behind the sim.

When you lose your SIM the operator demaps the MSISDN off the lost SIM's IMSI and maps it against a new IMSI.  But the same thing can't be done for number portability as IMSI and MSISDN are network dependent and cross-mapping is not allowed.

When you port your number:

• The new operator selects an unregistered MSISDN with its own network code.
• This information is stored on MNP server along with new IMSI and ICC-ID.
• This database is accessible by all networks.
• On dialling a number, operator from which call originates queries the MNP server (centralized database) to get routing information for the call.  The call is then completed with the new routing information.

The call routing can be illustrated as below:

• For a number ported from mobile operator B to operator C.
• If user from operator A calls, operator A seeks the routing information from MNP server.
• If information is received, the call is routed according to new information, If no information is received, the call is routed as per the routing information of original operator.