[VoiceOps] Question about SS7 routing

Paul Timmins ptimmins at clearrate.com
Wed Sep 2 17:56:47 EDT 2020

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> on behalf of Ross Tajvar <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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