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Module 4: Deployment Requirements

7 Digit vs. 10 Digit LRNs

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Local Number Portability
The next set of LNP Requirements that you should know about is 7 Digit LRN vs.10 Digit LRN Trunk Signaling.

  • Prior to LNP Implementation and/or Testing, when a service provider's LIS Trunking was turned up for service, many LIS Trunking groups were turned up with 7 digit signaling. In some cases, where 10 digits were requested, the signaling was changed to 7 digits as a result of discussions or activities between technicians.

  • According to the NANC LNP Architecture and Administrative Plan, "LRNs are 10 digit numbers that are assigned to the network switching elements (Central Office-Host and Remotes as required) for routing of calls in the network. The first six digits of the LRN will be one of the assigned NPA/NXXs of the switching element. The purpose and functionality of the last four digits of the LRN have not yet been defined but are passed across the network to the terminating switch."

  • Either a 7 or 10 digit LRN transmission option will work based on how the participating CLECs have set up their trunking and signaling network. It is vital that the CLECs on both ends of a trunk group understand what is being sent and received, and that the 7 or 10 digits are counted from right to left.

  • Technically, an LRN in a signaling message looks just like a phone number. The switch uses the LRN for routing information just like a called party phone number, therefore, the switch determines where to route a call by the NPA/NXX included in the LRN. This routing is based on the complex translations that are built into a switch. The Translations Routing Work Group uses the information from the Local Exchange Routing Guide (LERG) to determine where and how the NPA/NXX should be routed. This includes the number of digits signaled (SS7 or MF) on trunk groups that are to be used for trunking to a particular switch.
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