Number Portability

Ported Numbers Can Cause Calls to be Misrouted

Telephone service providers are assigned telephone numbers in blocks of 10,000 or 1000 numbers each.  The service providers use these blocks of numbers to provide ten digit telephone numbers to individual subscribers.  When a telephone service provider is assigned a block of numbers, the service provider is the “carrier of record” for those telephone numbers in the Local Exchange Routing Guide (LERG). In 1996 the FCC ordered that telephone companies must let subscribers switch service providers and keep their telephone number. Number Portability 40 Percent DiagramWhen you switch phone companies and keep your telephone number, your number is ported to the new service provider and added to the number portability database.  The ported telephone number is remains listed in LERG with the carrier of record that initially received the number, but the ported number is matched with the Location Routing Number (LRN) of the new service provider in the Number Portability Adminstration Center (NPAC).  The NPAC is the FCC sanctioned organization to manage the central database of all ported telephone numbers. Today, every call in North America starts with a query to the NPAC database to determine if the telephone number has been ported to a different service provider. If the number has been ported, then the NPAC returns the Location Routing Number (LRN) for the ported number. The call is then routed using the LRN, not the dialed telephone number.


Today there are 197 million ported telephone numbers in North America. TransNexus customers report that 40% of their calls are to ported telephone numbers. This development has a dramatic impact on least cost routing. If least cost routing is based on the dialed telephone number then 40% of all calls will not be routed to the lowest cost provider! TransNexus customers have found that number portability correction can decrease their total termination costs by over 15%.


Introduction to Number Portability

What do VoIP providers need to know about local number portability? This brief presentation touches on the following topics:

  • Understanding the Local Exchange Routing Guide (LERG)
  • Routing with Number Portability
  • What is a LRN?
  • Why VoIP Needs Number Portability
  • Least Cost Routing & Ported Numbers

View the TransNexus Introduction to Local Number Portability Presentation


TransNexus Products

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Optimized least cost routing requires software that can handle the complications of today’s VoIP industry. With NexOSS from TransNexus, you can easily provision rates, support up to 100,000,000 different VoIP routes, base LCR tables on inter-state rates, intra-state rates and customized local calling areas, and convert rate plans based on LATAs, OCNs and Tiers into a routing table and rate plans based on NPA-NXX-X breakouts. View NexOSS Details



OSPrey-NP is a simple, low cost, high performance software platform for hosting the U.S. number portability database locally within your network.  The OSPrey-NP server automatically stays synchronized with the U.S. Number Portability Administration Center (NPAC, to ensure that your network has a near real time copy of the NPAC. The OSPrey platform has been used in carrier operations since 2000.  OSPrey-NP is a specialized version of the OSPrey platform and is based on years of proven carrier grade reliability and performance.  Learn more about OSPrey-NP Number Portability solutions


Learn More


Local Number Portability: What VoIP Providers Need to Know (Astricon 2009)


Blog Posts

NPAC’s Take on Number Portability

Least Cost Routing Challenges

The LERG Is Becoming Obsolete



Mobile Number Portability Becomes Official in Ghana

The Benefits of Mobile Number Portability in Poor Service Countries