Local Number Portability (LNP) refers to the ability of a customer to maintain the same number when they switch carriers. For mobile phone lines, which include services like VoIP, this is known as Mobile Number Portability (MNP).
The way it works is that when a customer switches carrier, they’ll continue to be able to receive calls on the number they received from their old carrier.
Legislation to Allow Customers to Maintain Their Old Numbers
The Federal Communications Commission in the US published an order in November 2007 detailing new number portability obligations.
Interconnected carriers and providers must now be provided to customers. Subscribers were therefore enabled to change to another carrier without needing to change their number.
So, if you switch carriers, you’re able to take advantage of number portability. This is essential for businesses and individuals to avoid the time-consuming and expensive process of having to notify their clients and contacts about a change of number.
What is LNP/MNP?
LNP and MNP enable subscribers to keep the same phone number whenever they change carriers. Under the legislation detailed above, your previous carrier must route the old number to the customer’s new carrier.
The carrier will still assign a new number, which isn’t disclosed. The old number will then be mapped onto that.
Providers maintain a database of thousands of different numbers to achieve this. So, when someone calls a customer’s old number the call is initially received by the previous carrier. This is instantly rerouted to the new carrier.
To do this, carriers must use several porting references. All US carriers must protect and support consumers in this way, as mandated by the legislation of the FCC.
How it Works
Technically, LNP happens because of what’s known as a Location Routine Number (LRN). The LRN is a unique 10-digit number for each switch. LRN required no major changes to the public telephone network, which is why it became the ‘go-to’ method.
The first six digits of the LRN is used to route the call. It’s the 10-digit number that’s associated with the ported number.
If a carrier uses an automated process, the porting process occurs in a matter of minutes. Even when done manually, under FCC legislation the porting process is expected to be completed within a single business day.
The Challenge of Enabling Calls to Reach their Destination
There are numerous challenges faced by carriers when providing this service. VoIP, for example, is so cheap because it’s a Least Cost Routing (LCR) system.
When customers make calls through a VoIP service, they’re using an LCR system to route the call. Call routing and number portability are complex systems. With GSM portability currently in place, VoIP providers cannot rely solely on network root prefixes to route a call correctly. The VoIP provider must figure out which network every individual call is routed to.
This forces VoIP carriers to utilize MNP to route a voice call correctly. It’s made easier in the US because of a central database of numbers. In countries like the UK, it’s necessary to query the GSM network to figure out which network a number is with.