[VoiceOps] TNS SS7 Outage

[Mary Lou Carey]

That's really odd for all of your SS7 services to go down because 
carriers typically connect to 2 A-links which are backed up by 2 
D-links. So there are a total of 4 STPs (Signaling Transfer Points) 
programmed to back each other up. It could be down for one of two 
reasons.

In the SS7 network, each switch is assigned a unique point code (9 digit 
number that identifies the switch location). In order for the ISUP 
trunks to work, the SS7 provider has to establish a route between your 
switch and the other carrier's switch. To make it a little easier to 
understand let's pretend you have a switch in CA and you are connecting 
it to 3 of AT&Ts San Francisco tandems. If each switch had the following 
point code assignments:


Your switch's point code: 005-123-456
San Francisco tandem: 222-000-111
Oakland tandem: 222-000-222
Santa Rosa tandem: 222-000-333

Then your SS7 provider would build 3 point code routes:
Your switch 005-123-456 to AT&T San Francisco tandem 222-000-111
Your switch 005-123-456 to AT&T Oakland tandem 222-000-222
Your switch 005-123-456 to AT&T Santa Rosa tandem 222-000-333

When your customer makes a call that is served by the Oakland tandem, 
the call would be routed over the 005-123-456 to 222-000-222 route set. 
If your links work but the call doesn't complete either your route set 
failed for some reason, or either AT&T's SS7 links or trunks went down. 
I'd ask them where the failure occurred.

MARY LOU CAREY
BackUP Telecom Consulting
Office: 615-791-9969
Cell: 615-796-1111

On 2022-01-19 04:13 PM, Mike Hammett wrote:
> The links have since come back. This is the second major failure of
> TNS within 6 months. No RFO yet, but I will certainly be on them for
> some detail.
> 
> My Metaswitch support rep verified that (pardon my lack of using the
> correct terminology, I'm not that familiar with it) our SS7 links
> never actually went down, it just lost connectivity beyond that. Sorta
> like my BGP peer stayed up, but I lost the global routing table behind
> it.
> 
> -----
> Mike Hammett
> Intelligent Computing Solutions
> http://www.ics-il.com
> 
> Midwest Internet Exchange
> http://www.midwest-ix.com
> 
> -------------------------
> 
> From: "Mike Hammett" <voiceops at ics-il.net>
> To: "voiceops" <voiceops at voiceops.org>
> Sent: Wednesday, January 19, 2022 4:05:32 PM
> Subject: [VoiceOps] TNS SS7 Outage
> 
>  Does anyone have any information on the TNS SS7 outage going on now?
> Both of our A-links go to different facilities (Chicago and Ashburn)
> over different VPNs (which are up).
> 
> TNS has acknowledged that it's a carrier issue. That they're
> investigating.
> 
> -----
> Mike Hammett
> Intelligent Computing Solutions
> http://www.ics-il.com
> 
> Midwest Internet Exchange
> http://www.midwest-ix.com
> 
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