How LNP Works

A guide to LNP and telephone number routing

Local Number Portability (LNP) is possible thanks to the Location Routing Number (LRN), a unique 10-digit telephone number assigned to each switch. 

Prior to the establishment of LNP, a telephone number’s original state, rate center, Service Provider and carrier type (wireline, wireless, or VOIP) were identified in the North American Numbering Plan (NANP) by the NPA (area code) and NXX (central office code). With the introduction of LNP, telephone numbers were being ported between Service Providers and a new way of determining the network address of the serving switch was needed to ensure the call was routed correctly.  With that, the LRN was created. 

Porting a telephone number to another carrier

There are three reasons a telephone number might need to be ported:


How LRN Enables LNP

The LRN is a unique 10-digit telephone number assigned to each switch to support call routing through the Public Switched Telephone Network (PSTN). It serves as the network address and includes the NPA and NXX for a telephone number. A single LRN can be used for every ported number served between a switch and the NPA-NXX assigned location. The assignment of an LRN allows for LNP. 

Each telephone number entered into the NPAC’s records, is called a “Subscription Version” and contains the following information:

  • Current assigned Service Provider ID (SPID)
  • Service Provider type (wireless or wireline or VoIP)
  • LRN
  • SS7 Destination Point Codes 
  • Alternative SPID (optional)
  • Billing ID (optional)
  • End user location and type (optional)

The entire porting process can take just minutes. The Federal Communications Commission (FCC) has mandated simple one-number port requests be completed within one business day.

Call flow for ported telephone numbers

A call is made to a ported telephone number

  • The Initiating Service Provider’s switch launches a query to find out if the number has been ported
  • If yes the LRN of the new switch is provided
  • If not, the call is routed based on the telephone number

Steps of the LNP Porting Process

7 steps - how it works 09152020