Understanding Location Routing Numbers

All About LRN

An LRN is a unique number that uses a 10-digit telephone number format to efficiently and cost effectively route calls to numbers that have been ported or moved from one carrier to another. Essentially, the LRN assigns a unique 10-digit telephone number to each switch in a defined geographic area and this location routing number serves as a network address. Carriers routing telephone calls to customers that have transferred their telephone numbers from one carrier to another perform a database query to obtain the location routing number that corresponds to the dialed telephone number. The carrier would then route the call to the new carrier based on the location routing number.

For example, a local service provider receiving a 7-digit local call, such as 887-1234, would examine the dialed number to determine if the NPA-NXX is a portable code. If so, the 7­ digit dialed number would be prefixed with the NPA and a 10-digit query (e.g., 679-887-1234) would be dipped to the routing database. The routing database then would return the LRN (e.g., 679-267-0000) associated with the dialed number which the local service provider uses to route the call to the appropriate switch and then off to the end user.

Why do we use location routing number? The answer began in 1996 when the U.S. Congress mandated a change in local telephone service that allowed any carrier to enter a local market. This regulation meant that consumer’s phone services could be moved from one provider to another and the number remains with the consumer. Prior to this ruling the NPA-NXX determined where a number resided and how to route a call to this number. With the 1996 ruling, consumers could keep their number but a system was needed to determine where the number reside for providers to efficiently route calls. Part of the 1996 mandate was that every ported number must have an LRN assigned to it. NeuStar was chosen to develop and maintaine the Number Portability Administration Center (NPAC) to support local number porting.

Previously, the NPA-NXX was the method used to identify the state and rate center where the number was originally assigned, as well as the service provider and carrier type (wireless or wireline). As discussed above, LRN service was introduced to provide end users with the ability keep their numbers when they change providers. The LRN therefore replaced the need to identify rate center, state, service provider, and carrier type and only identifies the switch that the number is associated with. If a number has never been ported, it will not have an LRN, but will route based on the NPA-NXX of the number. Numbers that have been ported and consequently have an LRN, route based off the NPA-NXX of the LRN.

Above we discussed how LRN’s affect wholesale origination. Now let’s explore how LRN’s affect wholesale termination services. Most wholesale VoIP provider’s route termination calls using jurisdictional routing, which is comprised of interstate (between states) and intrastate (within one state) routes. Simply put, jurisdictional routing is based off the originating and the destination numbers. If the calling number is located in the same state as the called number, it is an intrastate call. If the calling number is located in a different state than the called number, it is an interstate call. Carriers using jurisdictional routing can choose to dip for the LRN (the most direct route) or they can choose to not dip for the LRN, but run the risk of paying a high rate for the call.

When a carrier uses jurisdictional routing for their termination, dipping for an LRN can often be a necessary evil. The below illustrations shows how NPA-NXX routing is more expensive than jurisdictional LRN routing as well as the rate difference between interstate and intrastate routes. Please keep in mind that this rate example is for calls to one number, and illustrates how the NPA-NXX of the LRN of the telephone number differs from the NPA-NXX of the actual telephone number.




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