Location routing numbers and LNP dips

See also

Sources

1. 1
   Bandwidth's outbound calling guide says its termination rate deck rates each call on the LRN of the dialed number, and the resulting least-cost-routing arrangement is only possible if the customer can perform an LRN dip on each call.

   Outbound calling integration guide · Outbound calling integration guide, section 'LRN billing' · Checked 2026-10-14
2. 2
   Bandwidth's porting glossary defines the LRN as the number used to route calls to the switch serving a number after it has been ported.

   Porting Terminology · Porting Terminology, glossary entry 'LRN' · Checked 2026-10-14
3. 3
   Bandwidth's porting glossary describes the LSMS as the function that updates SCPs and HLRs with mappings between ported telephone numbers and LRNs, and the SCP as mapping ported numbers to the LRN.

   Porting Terminology · Porting Terminology, glossary entries 'LSMS' and 'SCP' · Checked 2026-10-14
4. 4
   Under 47 CFR 52.26(b)(2), a local exchange carrier that receives an unqueried call to ported numbers from a carrier that should have queried may block that call only if performing the database query is likely to impair network reliability.

   47 CFR § 52.26 - NANC Recommendations on Local Number Portability Administration · 47 CFR 52.26(b)(2) · Checked 2026-10-14
5. 5
   47 CFR 52.21(e) defines a database method as a number portability method that uses one or more external databases.

   47 CFR § 52.21 - Definitions · 47 CFR 52.21(e) · Checked 2026-10-14
6. 6
   47 CFR 52.21(f) defines a downstream database as a database owned and operated by an individual carrier.

   47 CFR § 52.21 - Definitions · 47 CFR 52.21(f) · Checked 2026-10-14
7. 7
   In 47 CFR 52.26(b)(1), 'N' is the entity terminating the call to the end user, or a network provider contracted by that entity to provide tandem access.

   47 CFR § 52.26 - NANC Recommendations on Local Number Portability Administration · 47 CFR 52.26(b)(1) · Checked 2026-10-14
8. 8
   Under 47 CFR 52.26(b)(1), each designated N-1 carrier is responsible for ensuring that number portability database queries are performed on an N-1 basis.

   47 CFR § 52.26 - NANC Recommendations on Local Number Portability Administration · 47 CFR 52.26(b)(1) · Checked 2026-10-14
9. 9
   The N-1 query responsibility in 47 CFR 52.26(b)(1) does not apply where another carrier has already performed the query.

   47 CFR § 52.26 - NANC Recommendations on Local Number Portability Administration · 47 CFR 52.26(b)(1) · Checked 2026-10-14
10. 10
    47 CFR 52.26 requires local number portability administration to comply with the NANC recommendations and incorporates by reference the NANC Working Group Report dated April 25, 1997, with some sections excluded (including sections 7.8 and 7.10 of Appendix D).

    47 CFR § 52.26 - NANC Recommendations on Local Number Portability Administration · 47 CFR 52.26(a) and (c) · Checked 2026-10-14
11. 11
    Among the performance criteria in 47 CFR 52.23(a), a LEC's long-term number portability method must not degrade service quality or network reliability when customers switch carriers.

    47 CFR § 52.23 - Deployment of long-term database methods for number portability by LECs · 47 CFR 52.23(a)(5) · Checked 2026-10-14
12. 12
    47 CFR 52.33(a)(2) allows incumbent LECs to tariff a query-service charge that recovers only their carrier-specific costs of providing number portability query service, covering both prearranged and default-routed queries.

    47 CFR § 52.33 - Recovery of carrier-specific costs directly related to providing long-term number portability · 47 CFR 52.33(a)(2) · Checked 2026-10-14
13. 13
    The FCC's 1996 First Report and Order on number portability describes the LRN method as assigning a unique 10-digit telephone number to each switch in a defined geographic area.

    Telephone Number Portability (First Report and Order and Further Notice of Proposed Rulemaking, FCC 96-286, CC Docket No. 95-116), 61 FR 38605 · FCC 96-286 para 13 (61 FR 38605) · Checked 2026-10-14
14. 14
    FCC 96-286 describes the N-1 scenario as one in which the carrier immediately prior to the terminating service provider performs the database query or dip.

    Telephone Number Portability (First Report and Order and Further Notice of Proposed Rulemaking, FCC 96-286, CC Docket No. 95-116), 61 FR 38605 · FCC 96-286 para 42 · Checked 2026-10-14
15. 15
    In its 1996 First Report and Order the FCC declined to select a particular long-term number portability method and instead set performance criteria that any method must meet.

    Telephone Number Portability (First Report and Order and Further Notice of Proposed Rulemaking, FCC 96-286, CC Docket No. 95-116), 61 FR 38605 · FCC 96-286 paras 3 46 and 48 · Checked 2026-10-14
16. 16
    In the 1996 First Report and Order the FCC declined to specify which carrier must perform the database query, leaving carriers flexibility to negotiate.

    Telephone Number Portability (First Report and Order and Further Notice of Proposed Rulemaking, FCC 96-286, CC Docket No. 95-116), 61 FR 38605 · FCC 96-286 para 62 · Checked 2026-10-14
17. 17
    In the LRN method as described by FCC 96-286, the carrier performs a database query to obtain the location routing number that corresponds to the dialed telephone number.

    Telephone Number Portability (First Report and Order and Further Notice of Proposed Rulemaking, FCC 96-286, CC Docket No. 95-116), 61 FR 38605 · FCC 96-286 para 13 (61 FR 38605) · Checked 2026-10-14
18. 18
    FCC 96-286 required LECs in the 100 largest MSAs to offer long-term service provider portability beginning October 1, 1997, with phased deployment concluding by December 31, 1998.

    Telephone Number Portability (First Report and Order and Further Notice of Proposed Rulemaking, FCC 96-286, CC Docket No. 95-116), 61 FR 38605 · FCC 96-286 para 77 and Appendix F · Checked 2026-10-14
19. 19
    FCC 97-74 states that because the N-1 carrier performs the database query, most interLATA calls will be queried by the major interexchange carriers rather than the incumbent LECs.

    Telephone Number Portability (First Memorandum Opinion and Order on Reconsideration, FCC 97-74, CC Docket No. 95-116), 62 FR 18280 · FCC 97-74 para 70 · Checked 2026-10-14
20. 20
    FCC 97-74 states that a LEC that performs the query for an N-1 carrier may charge the N-1 carrier for performing it.

    Telephone Number Portability (First Memorandum Opinion and Order on Reconsideration, FCC 97-74, CC Docket No. 95-116), 62 FR 18280 · FCC 97-74 para 71 · Checked 2026-10-14
21. 21
    FCC 97-74 found that under LRN the database query takes the same amount of time for all calls, so LRN does not impair service quality when a customer changes carriers.

    Telephone Number Portability (First Memorandum Opinion and Order on Reconsideration, FCC 97-74, CC Docket No. 95-116), 62 FR 18280 · FCC 97-74 para 9 · Checked 2026-10-14
22. 22
    FCC 97-74 recognises that carriers may negotiate among themselves which carrier shall perform the database query.

    Telephone Number Portability (First Memorandum Opinion and Order on Reconsideration, FCC 97-74, CC Docket No. 95-116), 62 FR 18280 · FCC 97-74 para 70 · Checked 2026-10-14
23. 23
    FCC 97-74 says an originating carrier whose switch is not number-portability capable must either do the database query or arrange for another carrier to do it.

    Telephone Number Portability (First Memorandum Opinion and Order on Reconsideration, FCC 97-74, CC Docket No. 95-116), 62 FR 18280 · FCC 97-74 para 35 · Checked 2026-10-14
24. 24
    In its 1997 First Memorandum Opinion and Order on Reconsideration the FCC held that Query on Release (QOR) is not an acceptable long-term number portability method.

    Telephone Number Portability (First Memorandum Opinion and Order on Reconsideration, FCC 97-74, CC Docket No. 95-116), 62 FR 18280 · FCC 97-74 para 1 (62 FR 18280) · Checked 2026-10-14
25. 25
    iconectiv is the Local Number Portability Administrator for the United States, and the LNPA distributes ported number information to service providers.

    General FAQs | NPAC · General FAQs, question 'What is the Local Number Portability Administrator (LNPA) and what are its responsibilities?' · Checked 2026-10-14
26. 26
    iconectiv, the US LNPA, describes the LRN as a unique 10-digit telephone number assigned to each switch to support call routing, and says it serves as the network address.

    General FAQs | NPAC · General FAQs, question 'What is a LRN?' · Checked 2026-10-14
27. 27
    iconectiv describes the US NPAC as the system used to facilitate number porting in the United States, made up of seven regional systems.

    General FAQs | NPAC · General FAQs, questions 'What is the NPAC?' and 'What regions does the U.S. NPAC serve?' · Checked 2026-10-14
28. 28
    iconectiv's call flow for ported numbers has the initiating service provider's switch launch a query to find out whether the number has been ported; if it has, the LRN of the new switch is returned.

    How LNP Works | NPAC · How LNP Works, section 'Call flow for ported telephone numbers' · Checked 2026-10-14
29. 29
    In the NPAC, the LNPA assigns a Service Provider ID (SPID) to every approved applicant, and the SPID is part of the subscription version record for a ported number.

    How LNP Works | NPAC · How LNP Works, section 'Subscription version, explained' · Checked 2026-10-14
30. 30
    In iconectiv's call flow, if the query shows the number is not ported, the call is routed based on the telephone number itself.

    How LNP Works | NPAC · How LNP Works, section 'Call flow for ported telephone numbers' · Checked 2026-10-14
31. 31
    A switch that caches LRN dip results (Sippy allows up to 3 months) can keep routing a recently ported number to its old serving switch until the cached entry expires.inferred

    LRN Dipping and Number Portability · LRN Dipping and Number Portability, 'Configure LRN Dipping and Number Portability' step 3 · Checked 2026-10-14
32. 32
    If an upstream element marks a call with npdi without having performed a valid dip, a downstream RFC 4694-compliant element will not re-dip and will route on the dialed number, so a call to a ported number can be sent toward the donor network.inferred

    RFC 4694: Number Portability Parameters for the "tel" URI · RFC 4694 sections 5 and 5.1, combined with iconectiv How LNP Works 'Call flow for ported telephone numbers' · Checked 2026-10-14
33. 33
    A Telnyx v1.1 LRN ending in 9999 returned to a non-NPAC customer may be padding rather than the real switch LRN, so it should not be used as an exact LRN in trunk routing or in carrier escalations.inferred

    Migrate Your LRN Lookup API from v1 to v1.1 · Migrate Your LRN Lookup API from v1 to v1.1, non-NPAC example · Checked 2026-10-14
34. 34
    In 1997 the NANC recommended Lockheed Martin IMS and Perot Systems as the local number portability administrators for the seven US regional databases.

    The North American Numbering Council (NANC) Issues Recommendations Regarding the Implementation of Telephone Number Portability (DA 97-916), 62 FR 25157 · 62 FR 25157-25158, summary of NANC recommendations · Checked 2026-10-14
35. 35
    The Number Portability Industry Forum (NPIF), formerly the LNPA Working Group, publishes number portability best practices that reflect its consensus; an asterisk marks NANC endorsement and a double asterisk marks FCC adoption.

    Number Portability Best Practices · Number Portability Best Practices index page, introductory text · Checked 2026-10-14
36. 36
    RFC 4694 example C shows a dipped ported number as tel:+1-202-533-1234;npdi;rn=+1-202-544-0000.

    RFC 4694: Number Portability Parameters for the "tel" URI · RFC 4694 section 6 example C · Checked 2026-10-14
37. 37
    In RFC 4694, a global rn value is '+' followed by digits that MUST begin with a valid E.164 country code; visual separators are optional and are removed before use.

    RFC 4694: Number Portability Parameters for the "tel" URI · RFC 4694 section 4 · Checked 2026-10-14
38. 38
    Under RFC 4694, when an NP dip for a geographical number returns no routing number (the number is not ported), the node MUST still add npdi to the tel URI, without an rn parameter.

    RFC 4694: Number Portability Parameters for the "tel" URI · RFC 4694 section 5.2.1 and section 6 example D · Checked 2026-10-14
39. 39
    RFC 4694 defines the valueless 'npdi' (number portability database dip indicator) tel URI parameter, which tells downstream servers or switches that the NP database dip has already been performed.

    RFC 4694: Number Portability Parameters for the "tel" URI · RFC 4694 sections 1 and 4 · Checked 2026-10-14
40. 40
    Under RFC 4694, a node that receives a tel URI carrying npdi MUST NOT retrieve number portability information for a geographical number again, even if it is configured to do so.

    RFC 4694: Number Portability Parameters for the "tel" URI · RFC 4694 section 5.1 · Checked 2026-10-14
41. 41
    RFC 4694 requires a gateway converting from ISUP to include npdi in the tel URI when the ISUP ported number translation indicator (PNTI) bit is set to 1.

    RFC 4694: Number Portability Parameters for the "tel" URI · RFC 4694 section 5.2.4 · Checked 2026-10-14
42. 42
    Under RFC 4694, when an NP dip for a geographical number retrieves a routing number, the node adds both the rn parameter and npdi to the tel URI.

    RFC 4694: Number Portability Parameters for the "tel" URI · RFC 4694 section 5.2.1 · Checked 2026-10-14
43. 43
    RFC 4694 defines the tel URI 'rn' parameter, which carries the routing number associated with a telephone number that has been ported.

    RFC 4694: Number Portability Parameters for the "tel" URI · RFC 4694 sections 1 and 4 · Checked 2026-10-14
44. 44
    RFC 4694 allows a node that receives number portability parameters from an untrusted source to perform the NP database query again.

    RFC 4694: Number Portability Parameters for the "tel" URI · RFC 4694 section 5 · Checked 2026-10-14
45. 45
    RFC 4769 states that URIs returned by the pstn Enumservice may use the RFC 4694 tel URI parameters, and implementations must be prepared to accept them.

    RFC 4769: IANA Registration for an Enumservice Containing Public Switched Telephone Network (PSTN) Signaling Information · RFC 4769 section 1 · Checked 2026-10-14
46. 46
    RFC 4769 says npdi should be used in pstn Enumservice responses, and its ported-number example includes npdi so that later elements do not repeat the lookup in legacy PSTN databases.

    RFC 4769: IANA Registration for an Enumservice Containing Public Switched Telephone Network (PSTN) Signaling Information · RFC 4769 sections 3.1 and 4.1 · Checked 2026-10-14
47. 47
    RFC 4769 registers the 'pstn' Enumservice (E2U+pstn, with tel and sip subtypes) for carrying PSTN routing data, including number portability data, for E.164 numbers.

    RFC 4769: IANA Registration for an Enumservice Containing Public Switched Telephone Network (PSTN) Signaling Information · RFC 4769 sections 1 3.1 and 3.2 · Checked 2026-10-14
48. 48
    Sippy Softswitch can cache LRN dip results for a configurable period between 1 day and 3 months.

    LRN Dipping and Number Portability · LRN Dipping and Number Portability, 'Configure LRN Dipping and Number Portability' step 3 · Checked 2026-10-14
49. 49
    Sippy Softswitch needs npdi, rn and host in the LRN server's response; malformed or incomplete responses are discarded and the original called number is used.

    LRN Dipping and Number Portability · LRN Dipping and Number Portability, section 'The call flow with enabled LRN dipping is as follows' · Checked 2026-10-14
50. 50
    From its 2020 version, Sippy Softswitch can put the LRN result (rn and npdi) into the Request-URI of the outgoing INVITE to the vendor, as an environment-wide setting.

    LRN Dipping and Number Portability · LRN Dipping and Number Portability, section 'Starting from 2020 version...' · Checked 2026-10-14
51. 51
    Telnyx's Number Lookup API v2 (GET /v2/number_lookup/{number}) example response includes a portability object with lrn, spid, altspid, ocn, ported_status and ported_date fields.

    Quickstart for Number Lookup · Quickstart for Number Lookup, 'Basic number lookup example' response · Checked 2026-10-14
52. 52
    In Telnyx LRN Lookup v1.1, customers who are not permitted NPAC users get the real first six digits of the LRN with the last four digits padded as 9999; only customers with 'Permitted NPAC User' enabled get the full LRN.

    Migrate Your LRN Lookup API from v1 to v1.1 · Migrate Your LRN Lookup API from v1 to v1.1, non-NPAC example and Mission Control Portal steps · Checked 2026-10-14
53. 53
    Telnyx's LRN Lookup API v1.1 always returns a 10-digit LRN (NPA-NXX-XXXX), whereas v1 returned only the 6-digit NPA-NXX.

    Migrate Your LRN Lookup API from v1 to v1.1 · Migrate Your LRN Lookup API from v1 to v1.1, v1 and v1.1 response examples · Checked 2026-10-14

Documents

Cite this page

WarmTransfer. (2026, October 14). Location routing numbers and LNP dips. WarmTransfer. https://warmtransfer.net/knowledge/lnp-lrn-dips

@misc{warmtransfer-lnp-lrn-dips,
  title  = {Location routing numbers and LNP dips},
  author = {{WarmTransfer}},
  year   = {2026},
  url    = {https://warmtransfer.net/knowledge/lnp-lrn-dips},
  note   = {Verified 2026-10-14}
}