Jurisdictional routing

Jurisdictional routing is telephone call routing logic based upon the locations of the calling and called number and regulatory considerations.

Routing by state

Paradoxically, intrastate calls (i.e., calls within a state) generally cost more than interstate calls (from one state to another). For a service provider to optimize their least cost routing, they must have multiple tables, one for intrastate calls and another for interstate calls.

Indeterminate jurisdiction

Jurisdictional routing is determined by the ANI (Automatic Number Identification), or telephone number, of the calling party. With VoIP calls, it is common for the ANI to be an invalid value, such as a random number that is not a telephone number or the SIP URI of the calling party. Calls with an invalid ANI are also called indeterminate calls, since the call jurisdiction cannot be determined.

Some carriers may block calls that do not have a valid ANI. However, most carriers will accept and rate these calls at the higher intrastate rate if they are completed.

Indeterminate calls are effectively a third type of jurisdictional call, and full optimization requires a third least cost routing table.

Routing by LATA

Inter- and intra-LATA calls are yet another form of jurisdictional calls. LATAs (Local Transport and Access Areas) were defined by the Department of Justice in 1984 as the operating demarcation between local and long-distance telephone companies. Jurisdictional routing based on LATA was ubiquitous before the 1996 telecom deregulation act but now is rarely used.

Local routing

Local routing is another form of jurisdictional call routing that is determined by the NPA-NXX-X of the calling party and the called party. Interconnection of local calls is usually charged at very low rates—much less than intrastate calls—and offers another least cost routing optimization. The major challenge of local call routing is the lack of a uniform definition of local calling areas.

State and LATA boundaries are well defined, but there is no analogy for local calling areas, which are defined in tariffs filed by each Local Exchange Carrier (LEC). Local calling areas can range from very small, such as a wire centers, which are defined in the Local Exchange Routing Guide (LERG), to LATA-wide calling areas, which can include multiple area codes. (A telephone area code is also known as Numbering Plan Area or NPA.)

There are various local calling area definitions between wire centers and LATAs, such as expanded local calling areas and local toll areas.

Several firms maintain databases of all tariffs filed by local telephone companies and their defined local calling areas, including iconectiv, CCMI and KFR Services.

Routing table implications

An additional challenge with local call routing for most VoIP providers is the size of the table that defines the source and destination NPA-NXX-X combinations for each local calling area. Unlike Local Exchange Carrier switches that serve limited geographic areas, a VoIP service provider’s softswitch can serve customers anywhere in the US. A table that defines all the local calling areas in the US would have over a billion NPA-NXX-X combinations.

Telecom service providers need a way to define and maintain termination rates across all of the jurisdictions they serve. By keeping these routes and rates accurate and up-to-date, they can better control their pricing and operating margin.

To keep this data effective, daily updates should be made for local exchange routing (NPA-NXX and rate centers) to the LERG from the National Number Pool Administration. For example, TransNexus includes such updates with our NexOSS and ClearIP software products as part of the standard service.

Jurisdictional routing summary

Here’s a recap of the various types of jurisdictional routing described above:

  1. Local routing. Determined by the number blocks, or NPA-NXX-X, of the calling and called parties
  2. Intrastate routing. Calls between two points within the same state
  3. Interstate routing. Calls made from one state to another
  4. Intra-LATA routing. Calls between two points that are in the same LATA (Local Transport and Access Area)
  5. Inter-LATA routing. Calls made from one LATA to another
  6. International routing. Calls made from one country to another
  7. Invalid ANI, or indeterminate routing. Calls where the calling number is any value other than a valid telephone number—these are usually rated at the intrastate rate
Clicky