Weird Polycom Issue - Delayed Ringing

[pjr]

Hi All,

Our Polycom phones seem to have developed a strange behaviour recently. When called by 3CX (ie receiving an incoming call) the phone display will flash the call coming in, and the caller ID as you would expect but it wont actually ring for around 3-5 seconds.

It never used to do this - ie the display would flash and the ring would start simultaneously

Nothing has changed either in terms of 3CX or Polycom phone config.

It doesnt do this on internal phone to phone calls, but external calls cause this to happen, and calls made via the 3CX assistant (ie where it calls your desk phone first to connect you) exhibit this behaviour.

Has anyone seen this behaviour before?

Paul

 

[leejor]

It sound like something (download config/auto firmware update?) has changed, changes such as this don't start for no reason. Are all of the sets behaving this way? Are you sure that there was nothing done at the time this issue began?

Given that there is a difference between internal and external calls, could it be something related to caller ID, and perhaps name/address book look-up, or distinctive ring?

 

[pjr]

I have done further tests and am at a total loss as to explain it.

A single phone I have been using to test has exhibited the issue intermittently this morning - so nothing has changed and it cannot be firmware or template file changes as the phone has not been rebooted at all in between the issue being experienced.

It seems to come and go?

The issue occurs regardless of if an entry in the phone book calls it or it "makecall" from 3CX calls it, and the issue can happen and disappear with calls from the same number!

We have also had reports of the same issue occuring intermittently on 2 other 3CX systems we support with Polycom phones - again no changes have been made on any of these systems either.

Paul

 

[pjr]

Sussed it!

I found this post after some googling

http://community.polycom.com/t5/VoIP/VVX1500-ringing-delay/td-p/11794

Interestingly despite it being posted on the Polycom Support forums, the query is answered by Kevin from 3CX support.

The issue he describes is what is happening but I still had to do some more digging to find a resolution.

The behaviour I have seen relates to V10 installs using Polycom phones. In V10 Alert Info is sent in the SIP header and specifies the following URL http://www.notused.com

I believe something has changed in relation to that url recently (ie an A record for it now exists), and this has triggered the change in behaviour we are seeing.

To figure this out I did the following

pinged http://www.notused.com - this resolves to 141.8.224.25

I blocked access to this IP on the firewall of the affected sites but the problem remained.

I then did some internal testing with a Polycom phone and a mirrored port on a switch and can see for each call the phone queries DNS for that URL, gets the result 141.8.224.25 and attempts to reach it. Whilst it's trying this, the phone displays the call but the ringing doesnt start for a few seconds.

After further testing it appeared in this scenario the ringing problem was constant. Prior to this it was intermittent but happened 9 times out of 10. I didnt pursue this anomaly further as I needed to resolve it 100% of the time.

Next step was to prevent the phone from being able to resolve the URL at all. To achieve this I statically addressed a phone and didnt specify any DNS servers. This resolved the issue.

As all our client installs rely on DHCP for IP addressing, not specifying DNS servers was not an option so I then created a zone for notused.com on the DNS server on our LAN and didnt specify an A records for www. This also resolved the issue.

Luckily for the vast majority of our clients we manage their DNS servers as well as their VoIP, however, for some we dont meaning this isnt an option.

Having done some further digging it appears that support for Alert-Info wasnt introduced to 3CX until after V8 (we still have a lots of customers happily running V8 without this issue). In V10 (we skipped V9) the URL specified is http://www.notused.com and its not possible to change this.

In V11 3CX obviously realised their mistake and the URL specified is now http://www.notused.invalidtld and is also configurable in advanced parameters.

Now there's several hours of my life I will not get back all because someone specified a potentially valid domain for something that should never be valid by default!

Paul