[VoiceOps] Question about SS7 routing

Paul Timmins ptimmins at clearrate.com
Wed Sep 2 19:11:27 EDT 2020

  1.  You route it to the one that's least expensive, or provides the highest quality, or whatever your target market is. This part's really up to you and it's part of the differentiator of your product.
  2.  Apply for the blocks with NANPA/National Pooling after getting all the right licensure, interconnection agreements with whoever the local tandems are run by, then make a relationship with an AOCN (NANPA runs one) that can input your blocks into the LERG.
  3.  Reach out to your local tandem operators before doing this to work out the finer details of routing inbound calls. There are usually the local ILEC, but there are alternative tandem providers such as Inteliquent.
  4.  Realize that regardless, you may have to connect with many tandems, and several local phone companies to get proper inbound coverage for your numbers. Connecting in the Chicago LATA, this can be something like a minimum of 10-11 T1s to various tandems and trunk groups, in the Upper Penninsula of Michigan this could be two T1s to Marquette, MI, one for local/intralata calling, one for interlata calls.


From: Ross Tajvar <ross at tajvar.io>
Sent: Wednesday, September 2, 2020 6:10 PM
To: Paul Timmins
Cc: VoiceOps
Subject: Re: [VoiceOps] Question about SS7 routing

I see, that makes sense. So then I have two follow-up questions:

  1.  If you are connected to multiple carriers, e.g. multiple long distance carriers, how do you populate your routing table? (Obviously "it depends" but I'd be interested to hear an example.)
  2.  If you are setting up equipment for the first time, with a new number block, how do you make sure other people include you/your block in their routing tables?

On Wed, Sep 2, 2020 at 5:56 PM Paul Timmins <ptimmins at clearrate.com<mailto:ptimmins at clearrate.com>> wrote:

You only send calls to point codes you're connected to with ISUP trunks (what is a control network without bearer channels?), so you don't really do it that way. You would look at your usual LCR/routing table, and the adjacent switch you want to pass it to, be it a local end office, feature group D regional ILEC tandem, or long distance carrier wholesale circuit, and you would send it to the point code of the switch you're connected to that is the appropriate next hop for the call.

From: VoiceOps <voiceops-bounces at voiceops.org<mailto:voiceops-bounces at voiceops.org>> on behalf of Ross Tajvar <ross at tajvar.io<mailto:ross at tajvar.io>>
Sent: Wednesday, September 2, 2020 5:46 PM
To: VoiceOps
Subject: [VoiceOps] Question about SS7 routing

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?

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