LRN Compliance &
Routing Requirements
A practical guide for compliance officers, legal teams, and engineering leaders who need to understand where LRN lookup is legally required — and where it is a critical risk management tool.
FCC Number Portability Mandate
The FCC mandates that carriers support local number portability (LNP) and route calls based on the actual serving carrier — not the original assigned carrier. Failure to implement LRN-based routing results in misrouted calls and potential FCC enforcement action.
TCPA Pre-Dial LRN Requirements
TCPA litigation increasingly requires proof that callers verified wireless vs. landline status at time of call using a real-time LRN lookup — not a static list. A ported number may have changed status; using stale data is not a defensible TCPA safe harbor position.
Carrier Interconnect Routing Rules
Interconnect agreements between carriers require proper LRN-based call routing. Calls that fail to reach the serving carrier due to missing LRN data result in routing failures, billing disputes, and potential interconnect penalty exposure.
VoIP and IP-to-PSTN Routing
VoIP-to-PSTN gateways must perform LRN dips before terminating calls. Without the LRN, a SIP INVITE to a ported number will be rejected at the terminating carrier's point of interconnect — resulting in failed calls and degraded service quality.
What Compliance Teams Need to Know About LRN Data Freshness
Compliance decisions that depend on LRN data are only as defensible as the data is current. A number ported yesterday is unknown to a database updated last week.
NPAC processes number port completions within minutes. An LRN provider that refreshes its database in daily or hourly batches will systematically fail to reflect recent ports. For TCPA pre-dial verification, this means your wireless status check may be wrong at time of call — exactly the period that matters for liability.
SIPSmart replicates from NPAC-direct sources with replication lag measured in seconds. Every query reflects the most current available port data from the authoritative source.
Recommended Implementation for Compliance Use Cases
- Perform LRN lookup at the moment of dial initiation — not during list preprocessing
- Log the LRN response (including timestamp) alongside call records for audit trail purposes
- Treat a null or error LRN response as a reason-to-pause, not a reason-to-proceed
- For TCPA cases: retain LRN response records as evidence that wireless status was checked
LRN API with Compliance-Ready Logging
Every SIPSmart API response includes a timestamp and full routing data. Responses can be logged directly into your compliance record system.
- Yes for carriers. The FCC mandates LNP compliance under 47 C.F.R. § 52.1, which requires carriers to route calls to the actual serving carrier using LRN data. For non-carriers (call centers, VoIP applications), LRN lookup is a legal risk management tool — particularly for TCPA compliance, where wireless vs. landline status matters.
- The FCC has not issued an explicit technical mandate requiring real-time LRN queries for TCPA compliance. However, courts and TCPA litigation defense practitioners increasingly recognize that using stale wireless status data is a liability. Real-time LRN lookup at point of call initiation is the most defensible practice. Static lists scraped weeks ago do not reflect numbers ported after the list was created.
- LNP (Local Number Portability) is the regulatory concept — the right of subscribers to keep their number when switching carriers. LRN (Location Routing Number) is the technical mechanism — a 10-digit number appended to a SIP message or SS7 signal that tells the network which carrier currently serves the dialed number. LNP is the law; LRN is the implementation.
- Yes. A mobile number ported from AT&T to Verizon has a different LRN. Without lookup, a call from one mobile carrier to that ported number may misroute — billing the wrong carrier or failing to reach the subscriber's serving network. LRN lookup is required for complete routing accuracy across wireless, wireline, and VoIP originations.
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