So what does local number portability mean, and how does a local end office in the U.S.A. handle it?

I don’t like Rogers Telephone and want to move my service to Meta-Telecom. Local Number Portability (LPN) allows the subscriber to retain their local phone number even if they switch to another phone service provider. Allowing them to do this without impairment of quality and / or service. The Telecommunications Act of 1996 requires local exchange carriers (LEC) to provide this type of capability. The purpose for this is to remove the inconvenience of getting a new number every time the subscriber decides to change their local phone provider.

What happens once I decide to port my number to Meta-Telecom? Meta-Telecom will generate and send to the losing LEC an LSR, a End User Form and a Number Portability Form. The Losing LEC will respond with a Firm Order Commitment. Both LECS will execute the service order. Meta-Telecom will execute a Service Order Activation with NPAC. “Neustar” Both LECS will update 911 centers. Port should be completed.

Who owns the Ported Number Number blocks are assigned to OCNs. When a subscriber ports their phone number to a new service provider, the number is still assigned to the original OCN No limit on how many times a subscriber can port their telephone number. If a subscriber terminates their service, the number ‘snaps’ back to the original OCN.

Basic view of sub dialing ported number Lets go thru the steps that occur to hopefully make this call complete

In our call flow we have a customer “sub B” who has ported their number from LEC-A to LEC-B. And now “sub-A” on LEC-A is trying to call “sub-B”. LEC A subscriber Calls , a dn that Ported out of LEC A

When the call is placed. LEC-A will have in its dialing plan a trigger to launch a TCAP query to the SCP when is dialed. LEC-A sends a TCAP Query to the SCP

What is TCAP Transaction Capabilities Applications Part TCAP messages are designed for accessing databases or other switches to retrieve information or invoke features. TCAP is used to provide information to SSPs. This information is often used to enable successful call completion, but TCAP is not involved in the actual call-setup procedures.

The SCP receives the TCAP from LEC-A with a transaction Id and component portion. These tell the SCP who launched the query and for what reason. The SCP sees the Subsystem specified and does a lookup

The SCP will locate this dn in its database and return to LEC-A the LRN of the recipient switch LEC-B TCAP response to LEC-A

What is an LRN An LRN is an NPA-NXX Operating Companies (OCNs) are assigned number blocks (NPA-NXX) in the LERG Each switch (CLLI code) is assigned one or more NPA-NXXs The OCN assigns one NPA-NXX to be the LRN for each switch

LEC-A receives the response and will look in a LRN routing table to determine which outgoing trunk group to send the call. Check routing tables to determine outgoing tgrp

LEC-A will send an IAM to LEC-B via the STP. This IAM will contain the LRN and the GAP.

What is a GAP? GAP is by definition; Generic Address Parameter. When a originating switch launches a TCAP and receives a response it will modify the IAM message sent out. The original called number becomes the GAP parameter in the IAM. The LRN becomes the called number

LEC-B sees the GAP in the IAM and determines that number now terminates on their switch and the call is routed to subscriber-b

Let’s dissect a portion of a TCAP message MTP SND >> LNK : 0 LST : 0 DPC (NCM): OPC (NCM): SLS: 3 SIO S I : 3 H1H0:9=MSG TYPE MSG : b b c3 f8 28 8b 01 2f e2 2d c7 04 5c e e8 25 e9 23 cf d a bf d f f CALLED PARTY= CALLING PARTY = TRANSLATION TYPE=11 SUBSYSTEM NUMBER=248=LNP MTP RCV << LNK : 0 LST : 0 DPC (NCM): OPC (NCM): SLS: 6c SIO SI : 3 H1H0:9 MSG : c1 f8 02 c1 f8 1f e4 1d c7 04 5c e e8 15 e9 13 cf d f LOCATION ROUTING NUMBER= c1= =Subsystem indicator 0 =Point Code indicator 0000 =Global Title indicator 1=Routing indicator (1= route by DPC & Subsystem )

Now we can look at the IAM being sent out by the originating SSP. ISUP SND >> LNK : 0 LST : 0 DPC (NCM): OPC (NCM): SLS: 3 SIO SI : 5 ISUP MSG TYPE:1 CIC:6 MSG : a d a a ea c c0 08 c MSG TYPE:1 =Initial Address Message Generic Address Parameter= Calling party Number= Called Party Number= , this is the LRN Originating line info=No special treatment Jurisdictional Information Parameter= Forward Call Indicator Bit M:Transalated Number Indicator=1 The receiving end will see the GAP field populated in the incoming IAM determine it can route the call and send back an ACM ISUP RCV << LNK : 1 LST : 1 DPC (NCM): OPC (NCM): SLS: df SIO SI : 5 ISUP MSG TYPE:6 CIC:6 MSG : Message Type:6= Address Complete Message

This gives us a basic idea of how an LNP call is treated A little bit more than just a connection from phone A to phone B.