What Is an LRN?
A Location Routing Number (LRN) is a 10-digit number assigned to a telephone switch that tells the network where to route a call. It is the backbone of number portability in the North American telephone system.
The Problem LRNs Solve
Before number portability, phone numbers were tied permanently to specific telephone switches. If you switched carriers, you got a new number. This created massive friction for subscribers and locked them into their original carrier.
The FCC mandated Local Number Portability (LNP) in 1996, requiring carriers to allow subscribers to keep their numbers when switching providers. But this created a technical problem: how does the network know where a ported number is currently routed?
The solution is the LRN. Instead of routing calls to the original switch where a number was assigned, carriers query NPAC for the current LRN, which points to the actual active terminating switch — regardless of which carrier it belongs to.
How LRNs Work
When a subscriber ports their number from Carrier A to Carrier B:
- Carrier B submits a porting request to NPAC
- NPAC updates its database with the new LRN pointing to Carrier B's switch
- NPAC distributes the update to all authorized service providers
- Any carrier routing a call to that number now looks up the LRN and routes accordingly
LRN vs. Dialed Number
The dialed number (DNIS) is what the caller entered. The LRN is what the network uses to route that call. For non-ported numbers, they often share the same NPA-NXX. For ported numbers, they are different — the LRN points to where the number actually lives now.
What Data Is in an LRN?
An LRN query typically returns:
- LRN — The 10-digit location routing number
- OCN — Operating Company Number (carrier identifier)
- SPID — Service Provider ID
- Rate Center — Geographic rate center
- LATA — Local Access and Transport Area
- Ported Flag — Whether the number has been ported
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SIPSmart provides real-time LRN lookups via NPAC-direct API. 1,000 free queries to start.
- LRN stands for Location Routing Number. It is a 10-digit number assigned to a telephone switch that serves as the routing address for calls destined to numbers on that switch.
- Not always. For non-ported numbers, the LRN often matches the NPA-NXX of the dialed number. For ported numbers, the LRN is different — it points to the current terminating switch, not the original one where the number was first assigned.
- NPAC (the Number Portability Administration Center), now operated by Telcordia/iconectiv under FCC authority. All carrier number portings are submitted to NPAC, which distributes LRN updates to authorized service providers.
- No. LRNs are specific to the North American Numbering Plan (NANP), covering the US, Canada, and associated territories. Other regions use different portability systems (e.g., ENUM-based HLR lookup in Europe).
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