Local Number Portability (LNP) is made possible by the Location Routing Number (LRN) associated
with the telephone number upon porting. The LRN is a unique 10-digit phone number that is allotted to a specific switch. The LRN approach made it conceivable to present LNP without drastically changing the Public Switched Telephone Network (PSTN). It permitted the current routing platform to stay set up, allowing a progressive transformation of the system to deal with LNP traffic.

Before LNP was introduced, the NPA-NXX of a phone number distinguished the state and rate center where the number was initially assigned, the service provider, and the carrier type (wireline or wireless). Today, since phone numbers have been ported amongst wireline and wireless service providers, the NPA-NXX of a phone number just reflects the state and rate center where the number was initially assigned. The LRN’s NPA-NXX currently fills in as the network address that enables communications service providers to cost-successfully route calls and traffic to their legitimate stopping points.

Calls are routed based on the initial six digits (NPA-NXX) of the phone number. The NPA-NXX is
the address of the switch serving the phone number. At the point when a number is ported, the
10-digit LRN is tied to the ported number. Calls to the ported number are then routed in light of
the NPA-NXX of the 10-digit LRN.


NPA Number Plan Area (Area Code)
NXX Prefix (Central Office Code)
XXXX Line Number
N Can be any number from 2 to 9
P & A Can be any number from 0 to 9
X Can be any number from 0 to 9


(425) 941 – 0507
is an area code assigned in Washington
425-941 is an exchange assigned to Cellco Partnership dba Verizon Wireless, associated with the Bellevue rate center and served from the switch STLLWAZUCM3
0507 is the line number assigned to the iconectiv PBX

When porting a number to another service provider, there are three scenarios that define why
telephone numbers are ported: intercarrier/competitive porting, intracarrier porting, and number
pooling (in the United States).

Porting TypeDescriptionWhy It Matters
Intercarrier or CompetitiveMoves the number from the
carrier currently providing
service to the carrier that will
be providing service.
Changes both the switch
where the number resides
and the carrier providing service
to the end-user.
IntracarrierAdds a record in the NPAC;
may also move a number
from one switch to another
within the same carrier’s network.
Used when a carrier that holds
the number puts it in the
NPAC for reasons other than
competitive porting. There is
no change in carrier.
Number PoolingNumbers are assigned to a
new service provider in 1,000
blocks to create an inventory
of unassigned phone
numbers, e.g., 425-941-1000
through 1999.
These number blocks are put
in the NPAC. Calls to a telephone
number in the block
must be routed by the block’s
LRN unless the block is in the
same switch as its NPA-NXX.


To further understand Local Number Porting, let’s look at the steps that are required to complete
a wireline port in. Below is a summary of the processing steps and essential porting process
for a common local number port. In this particular example, the end-user is switching to a
new service provider and wants to keep his/her existing telephone number.

  1. The new network service provider (NNSP) must first confirm that they have coverage in the particular geographic area that the end user is porting in. Until national number portability (NNP) is fully realized, providers are still restricted, geographicaly, to the areas in which they have a network presence.
  2. The NNSP must have an agreement in place with the old network service provider (ONSP) that allows them to port numbers from the ONSP’s network/SPIDs. These agreements, known as trading partner agreements (TPAs), or trading partner profiles (TPPs), or interconnection agreements (ICAs) depending on the carrier, can be a simple e-mail exchange, or a lengthy legal process.
  3. The NNSP collects the end user’s information that should be on file with the ONSP, including: account name, service address, account number, and other identifiers.
  4. The NNSP either requests a customer service record (CSR, if available) to confirm the information provided (to prevent number slamming and ensure the transaction is valid), and/or submits a local service request (LSR) containing the porting telephone numbers and account information to the ONSP.
    • The method by which a CSR and/or LSR is submitted highly varies depending on the carrier. Some require the information be sent via an e-mail in a Microsoft Excel document, some send rich-text formatted (.rtf) documents, others have portals/GUIs that require user logins, and others offer API end-points to carriers.
  5. The ONSP reviews the LSR and either provides a firm order completion (FOC) date
    when the numbers can be migrated, or rejects the LSR if there is a data mismatch.
    • If an LSR is rejected, carriers are able to update the LSR and re-submit, in a common review/resubmit/reject cycle.
  6. Upon receiving FOC, the NNSP uses their LTI/SOA of choice to interact with NPAC, and build subscription versions (SVs) for the porting telephone number, that include: information outlining who is gaining the number, who is losing the number, the modality of the transfer (wireline to wireline, wireline to wireless, etc.), and which LRN the number should be associated with upon transfer.
    • Depending on the carrier, the ONSP will either concur these records (and provide matching information using their preferred NPAC-connected system), let pre-set timers expire, or do nothing at all.
  7. On the FOC date (or within a grace period agreed upon by the carriers), the NNSP will send an activation request to NPAC using their SOA/LTI and the phone numbers will have to be updated to reflect new ownership by the NNSP.
    • This activation is processed within milliseconds, and is broadcasted
      across the industry so that telecom carriers can update their routing
      records and ensure calls are correctly routed to the NNSP.
    • There should be little to no downtime for the end user at the time of
      the transfer, and the transfer should be seamless.

Barring any mistakes or issues with validations and notifications, the time in which LNP occurs varies greatly across the industry. Those carriers that leverage automated solutions for processing requests can usually do so inside minutes. This is especially true for wireless ports, as most wireless carriers are interconnected through a single LNP gateway, and very little information is required to validate wireless ports. However, for wireline carriers that do not have automated solutions, the LNP process can take weeks or over a month to fully process (depending on the quantity of numbers porting), due to the manual labor required to parse and administrate the changes.

In an attempt to simplify porting of services of a single line without features, the FCC implemented
simple porting rules. These rules state that a simple port (a port that only has a single line
associated with the account, does not include features, and does not involve a reseller) must be
completed within one business day as long as the porting information is accurate. (This is often
debated. Some VoIP carriers often get single TN port requests (simple) but take a few days to
process it as the architecture is different than TDM, and they often rely on other providers/resellers
to get network access).

At the point when a call is made to the ported phone number, the originating service provider
switch dispatches a query to its LNP call routing database to decide if the phone number has
been ported. If it has, the database reply gives the switch the LRN necessary to legitimately route
the call. If the number isn’t ported, the database reply makes known that the call ought to be
routed based on the phone number. At the point when various switches are engaged in the call
path, the second to last carrier has the obligation to perform the LNP database query if one has
not been made (the FCC has since eliminated this “N-1” rule on July 12, 2018).

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