Local number portability (LNP) for fixed lines, and full mobile number portability (FMNP) for mobile phone lines, refers to the ability of a "customer of record" of an existing fixed-line or mobile telephone number assigned by a local exchange carrier (LEC) to reassign the number to another carrier ("service provider portability"), move it to another location ("geographic portability"), or change the type of service ("service portability"). In most cases, there are limitations to transferability with regards to geography, service area coverage, and technology. Location Portability and Service Portability are not consistently defined or deployed in the telecommunication industry.
In the United States and Canada, mobile number portability is referred to as WNP or WLNP (Wireless LNP). In the rest of the world it is referred to as mobile number portability (MNP). Wireless number portability is available in some parts of Africa, Asia, Australia, Latin America and most European countries including Britain; however, this relates to transferability between mobile phone lines only. Canada, South Africa and the United States are the only countries that offer full number portability transfers between both fixed lines and mobile phone lines, because mobile and fixed line numbers are mixed in the same area codes, and are billed identically for the calling party, the mobile user usually pays for incoming calls and texts; in other countries all mobile numbers are placed in higher priced mobile-dedicated area codes and the originator of the call to the mobile phone pays for the call. The government of Hong Kong has tentatively approved fixed-mobile number portability; however, as of July 2012, this service is not yet available.
Some cellular telephone companies will charge for this conversion as a regulatory cost recovery fee.
History LNP was invented by Edward Sonnenberg while working for Siemens.
Though it was introduced as a tool to promote competition in the heavily monopolized wireline telecommunications industry, number portability became popular with the advent of mobile telephones, since in most countries different mobile operators are provided with different area codes and, without portability, changing one's operator would require changing one's number. Some operators, especially incumbent operators with large existing subscriber bases, have argued against portability on the grounds that providing this service incurs considerable overhead, while others argue that it prevents vendor lock-in and allows them to compete fairly on price and service. Due to this conflict of interest, number portability is usually mandated for all operators by telecommunications regulatory authorities. In the US, LNP was mandated by the Federal Communications Commission (FCC) in 1996. The mandate required all carriers in the top 100 metropolitan statistical areas (MSAs) to be "LNP-capable" and port numbers to any carriers sending a BFR (bona fide request). The ability to keep a number while switching providers is thought to be attractive to consumers. It was also a major point made by CLECs (competitive local exchange carriers) preventing customers from leaving ILECs (incumbent local exchange carriers), thus hindering competition. Details regarding the reasons for LNP and how it is to be implemented can be found in the First Report and Order referenced above.
In the US, the FCC has mandated this in order to increase competition among providers. As of late November 2003, LNP was required for all landline and Wireless common carriers, so long as the number is being ported to the same geographical area or telephone exchange. This latest mandate included carriers outside the top 100 MSAs that previously enjoyed a rural carrier exemption.
Portability schemes There are four main methods to route a number whose operator has changed.
All Call Query (ACQ) The operator that originates the call always checks a centralized database and obtains the route to the call. The originating operator then routes the call to Serving Network.
Query on Release (QoR) The operator that originates the call first checks with the operator to which the number initially belonged, the donor operator. The donor operator verifies the call and informs that it no longer possesses the number. The operator that originates the call then checks the centralized database, as is done with ACQ.
Call Dropback Also known as Return to Pivot (RoP). The operator that originates the call first checks with the donor operator. The donor operator checks its own database and provides a new route. The operator that originates the call then uses this route to forward the call. No central database is consulted.
Onward Routing (OR) The operator that originates the call routes the call to the donor operator. The donor operator checks its own database and obtains a new route. The operator to which the number was designated routes the call to the new operator. This model is called indirect routing.
Technical issues Complexity for number portability can come from many sources. Historically, numbers were assigned to various operators in blocks. The operators, who were often also service providers, then provided these numbers to the subscribers of telephone services. Numbers were also recycled in blocks. With number portability, it is envisioned that the size of these blocks may grow smaller or even to single numbers. Once this occurs the granularity of such operations will represent a greater workload for the telecommunications provider. With phone numbers assigned to various operators in blocks, the system worked quite well in a fixed line environment since everyone was attached to the same infrastructure. The situation becomes somewhat more complex in a wireless environment such as that created by cellular communications.
In number portability the “donor network” provides the number and the “recipient network” accepts the number. The operation of donating a number requires that a number be “snapped out” from a network and “snapped into” the receiving network. If the subscriber ceases to need the number then it is normal that the original donor receive the number back and “snaps back” the number to its network. The situation is slightly more complex if the user leaves the first operator for a second and then subsequently elects to use a third operator. In this case the second operator will return the number to the first and then it is assigned to the third.
In cellular communications the concept of a location registry exists to tie a “mobile station” (such as a cellular phone) to the number. If a number is dialed it is necessary to be able to determine where in the network the mobile station exists. Some mechanism for such forwarding must exist. (For an example of such a system, see the article on the GSM network.)
In the US, there are standards for portability defined by the FCC, the LNPA, NANPA and the ATIS which are agreed upon by all member providers to help make LNP as cost-efficient and expedient as possible while still retaining a healthy level of security for all providers and in respect of the highest level of customer service. These rules, first defined in the 1st, 2nd and 3rd Reports and Orders by the FCC (publicly available at fcc.gov), are further detailed by the LNPA in order to ensure any provider can successfully port numbers to any other provider. iconectiv provides a national database called the NPAC (National Portability Administration Center) which contains the correct routing information for all ported and pooled numbers in the US and Canada. The NPAC maintains detailed documentation of the procedure common among US carriers to port numbers as described here.
Providers use SS7 to route calls throughout the US/Canada network. SS7 accesses databases for various services such as CNAM, LIDB, VSC and LNP. Calls to ported numbers are completed when a customer who calls a ported number sends the dialed number to a provider's SSP (Service Switch Point), where it is identified either as a local call or not. If the call is local, the switch has the NPA-NXX in its routing table as portable, so it sends a routing request to the Signal Transfer Point (STP) which accesses a local database that is updated by an LSMS (Local Service Management System) which holds all routing for all ported numbers to which the carrier is responsible for completing calls. If routing information is found, a response is sent to the "query" containing the information necessary to properly route the call. If it is not a local number, the call is passed on to the STP and routed until it gets to a local carrier who will perform the "query" mentioned earlier and route the call accordingly.
The routing information necessary to complete these calls is known as a Location Routing Number (LRN). The LRN is no more than a simple 10-digit telephone number that resides in the switch of the service provider currently providing service for the ported telephone number.
When a provider receives a request to port a telephone number from a new customer, that provider sends an industry-standard Local Service Request (LSR) to the existing (or "old") provider. When the Old Provider receives this request, it sends back Firm Order Confirmation (FOC) and the process of porting the number(s) begins. Either provider can initiate the port using a Service Order Activator (SOA or LSOA) which directly edits the NPAC database mentioned before. Providers can also make these requests within the NPAC database directly. If the new provider initiates the port, it is called a "pull," and if the old provider initiates, it is a "push." Once the number is pulled or pushed, the providers must concur the request and the new provider must "activate" the number using the LRN of the switch serving the customer on the agreed due date. At the point this is completed, the number is ported.
Much of this process is duplicated in intermodal portability (porting between wireline and wireless providers). There are a few technical differences, however, in WLNP—Especially with concern to the time intervals allowed.
Fax and paging numbers Some service providers, especially related to fax services, do not qualify as a "local exchange carrier" or other form of telecommunications carrier.47 USC 251(b)(2): Each local exchange carrier has the following duties: *** (2) The duty to provide, to the extent technically feasible, number portability in accordance with requirements prescribed by the Commission. 47 U.S.C.A. § 153(32): The term “local exchange carrier” means any person that is engaged in the provision of telephone exchange service or exchange access. Such service providers may be the "customer of record" from the LEC's perspective. As a result, the applicable law may not require that such service provider port out the number to another provider. Users and providers often negotiate portability and port out fees. eFax is one vendor that claims it is not a telecommunications company and does not allow porting out of numbers originally assigned by them to their customers; however, numbers ported by customers into eFax may be ported out.
A fax machine connected to its own physical telephone line at the subscriber's premises is portable in the same manner as any other standard wireline service. Distinctive ring sometimes poses problems, as one landline may have two or three numbers with a fax or dial-up modem programmed to answer just one of the secondary numbers on the line. Porting out the main number will usually unsubscribe the entire line, disconnecting the secondary numbers without moving them to the new provider.
In Canada, pocket pager answering services are exempted from all local number portability requirements. The same is not true of mobile telephones, which are fully portable to another carrier or another service type (such as landline or voice over IP) within the same local interconnection region.