Schools Broadband and Xelion

[gpjt]

Morning,

 

I have an ongoing issue that is causing many frustrations and wonder if anyone can offer any advice after going back and forward to SBB?

 

We have SBB as our ISP and a Xelion VOIP system.

 

Fail over line (80/20) VOIP works fine, yet on the main leased line (sky 1gig) we have an unusable phone system. We also have the same setup at another school and all is fine there, yet SBB can't get to the bottom as to why there are issues on the leased line at the other site.

 

TIA

[PaddyNewman]

Is your firewall on prem? Packet capture not giving you any hints?

 

 

[gpjt]

Firewall is with the ISP. We've ran a diagnostic check both on the fail over and main line using Xelions software. All that it showing is an issue with the Jitter connection. Some further changes have been made and ready to test.

[ChetterHummin]

When you say unusable on the Sky line, is it a case of very poor call quality or are the phones failing to connect at all over it?

[gpjt]

Calls are so poor in quality on the main line, that we have the school using their fail over line which works fine. As of today calls made by the school are the issue. Incoming and internal calls are fine.

[PaddyNewman]

Your other school thats all fine, does that have the same firewall, I would assume fortigate and different vdom but the same physical hardware?

 

The lines, are they presented on prem to a single router and is there any qos on the router (assuming its just an NTU/router on prem with 2 feeds in)

 

Unsure what to suggest without seeing captures and the like, it just sounds like theres a problem that ISP and VoIP company need to lock together with, captures and debug on sip to see what's going on. Raw sip and rtp captures usually give you significant info, unless SIPS then...ugh. 

[ChetterHummin]

I've done some VoIP in my time and my hunch here is the codec the outbound calls are being negotiated in is causing the issue.

 

There are different codecs a VoIP system can negotiate to use- they are usually set at the config level. See if your VoIP provider can set a different codec to be preferred/higher up the priority list. See below an example:

[ChetterHummin]

To give more context: If inbound calls are fine, we know its not just an issue with the line. Otherwise any call going over it would have the same issue, whether inbound or out.

 

Outbound calls will follow the codec priority list of your own VoIP system, whereas inbound calls will have the remote side's codec priorities.

 

Internal calls would be fine since they wouldn't go over the Internet line. In other words, a particular codec likely isn't performing well over that Sky line for some reason.

[gpjt]

To update this thread,

 

SBB managed to find the issues and have resolved them. It was caused by packet duplication. 

 

Many thanks to them for sorting the issues out. It took longer than i'd hoped after escalation to a more senior engineer who identified the problem and resolved it.