I'll try to make this as short and sweet as possible even though it's pretty complicated. Point Codes are the 10 digit addresses for a particular switch and LRNs are the 10 digit addresses for a particular connection point that switch is associated with. In the PSTN world, all connections are dedicated and implemented by LATA / Tandem area for Local / IntraLATA traffic. When you get your first NPA-NXX for a LATA / tandem area, you enter it in the LERG (National Routing Database) and populate the tandems (Local, IntraLATA and FGD) that you are connecting to. Then you assign a 10 digit phone number from your NXX block to be your LRN. You add that to both the LERG and NPAC (National Porting Database). Once you've published all your switch information in the LERG and NPAC, then you establish your ISUP trunks with each ILEC you're interconnecting with. You can set up additional trunks with other carriers if you want a cheaper option for routing traffic, but the minimum required is the ILEC. Each carrier's switch will have a distinct point code associated with it so you'll order ISUP trunks to each switch (point code route) you need to be connected to. You'll also associate the distinct LRN for that LATA / carrier tandem area with that trunk group. Usually there's multiple trunk groups per LATA / tandem area so you'll program your routing tables with the NPA-NXXs each trunk group serves. That way when a customer originates a call, your switch can do the LNP dip to find the LRN and send it over the route that the NPA-NXX of the LRN is associated with. Routing tables can get complicated depending on how many carriers you're connected to. Companies that operate in more than one ILEC area or LATA usually purchase Least Cost Routing software so they can send their originating traffic out over the cheapest route. IXC traffic is routed a little differently because it is routed by CIC (4 digit code that identifies the IXC) rather than by NPA-NXX. They connect to all the ILEC carriers just like the CLECs do, but they populate their routing information in the SMS database instead of the NPAC database. Once the call is dipped, the traffic is delivered in pretty much the same way.....by dedicated trunk group / tandem area. MARY LOU CAREY BackUP Telecom Consulting Office: 615-791-9969 Cell: 615-796-1111 On 2020-09-02 04:46 PM, Ross Tajvar wrote:
Hi all,
I'm trying to understand how routing works in SS7-land. I am familiar with portability, and I know (at least in the US) the first step in routing a call is doing an LNP dip to get the LRN.
However, it looks like addresses in MTP3 are "point codes" (PCs) which are assigned to switches. Calls are set up with ISDN-UP, which is transported via MTP3. So in order for a call to be set up, the destination switch's PC must be known. How is the destination PC determined from the destination LRN?
Thanks, Ross _______________________________________________ VoiceOps mailing list VoiceOps at voiceops.org https://puck.nether.net/mailman/listinfo/voiceops