Solved Yealink T48S Calls Failing when using prefix

[pmterp]

On a new server that was installed yesterday (v16), 3CX pushed firmware 66.84.0.35 for the Yealink T48S phones at the client's location.
The location is using POTS lines from 2 providers into 2 separate Patton SN4114s. There are no issues with 3CX or the Patton devices, that info is just for reference.
We were using the first 2 DSS keys to prefix a single digit, 7 or 8 and then using outbound rules to send the call to the appropriate Patton device.
Pressing the first DSS key would prefix a 7, the user would then dial the phone number, press send and the call would go through Patton #1.
Pressing the second DSS key would prefix an 8, the user would then dial the phone number, press send and the call would fail on the Yealink phone (it was not even being sent to the 3CX server or Patton #2).
I swapped the prefixed digits and still calls using the first key (now prefixing an 8) would go through but calls using the second key would still fail.
We then moved the prefix keys to DSS keys 7 and 8 and both worked so I assumed it was a Yealink bug when using DSS key 2 for prefixing. However, this morning, the users are reporting any calls attempted with the prefix keys (DSS keys 7 and 8) are failing again. They can manually dial a 7 or 8 and then the number and the call goes through.

I'm curious if anyone else has experienced this or could test to see what their results are. I have a Yealink T52S on my desk and I've tested it without issue here.

 

[Saqqara]

How have you provisioning the phones, thru normal 3CX procedure or manually.

How are you changing the DSS keys, guessing it's via the phone webend as 'Prefix' is not one of the options you can select when programming the dss keys within the 3CX management console.

If you are using 3CX normal setup, any manual changes to the DSS keys will be overwritten by the overnight provisioning of the phone.

When it does not work, can you login the web frontend of the phone and check the dss key settings.

 

[pmterp]

We're using a custom template to place the DSS keys which I know isn't officially supported. No other changes have been made to the template.
Even when the call fails, you still see the digit prefixed as expected. So if they hit the 2nd key in the original setup, they'd see the "8", then dial the number, then press SEND, then they would see CALL FAILED on the display and no record of the call in 3CX.

 

[eddv123]

Custom templates can be a minefield so ensure you have enough experience before attempting to create them (obviously).

I know it is highly likely to be a phone issue so you might want to run the logging in level 6 mode and a PCAP from the phone itself (great that Yealink support this feature) and see what happens when you input the DTMF.

You could raise this with Yealink support, the are very helpful.

 

[eddv123]

I think based on your response that you have narrowed down the fault to the Yealink however if you want further clarity run the PCAP from 3CX also to see if the call is reaching the PBX: https://www.3cx.com/docs/capture-network-traffic/

 

[Allen_Miller]

Just kind of wondering if all you are trying to use the DSS key for is to add a single digit (prefix) in the beginning of a dialed phone number - why don't you just forget the DSS key and just dial the single digit? I guess I must be missing something?

 

[eddv123]

@12494 yes i thought along the same lines, or adding the prefix on an outbound rule or even on the Patton gateway itself (Which too would require a little adjustment to the 3CX template).

 

[pmterp]

Thanks for the replies. We've resolved the issue.
We had a working custom template that was created on 15.5SP6 while the phones were on a lower firmware that we copied from. The client is now on V16 which pushed a new Yealink firmware.
On the older firmware, a designation for the "line" for the DSS key when using type 40, prefix, was not required (and shouldn't be required). When configuring the keys manually through the phone's web UI, the line field is unavailable when you select prefix as the type.
On the new firmware, setting a DSS key via the provisioning template without assigning a "line" causes the key to use the line equal to the key number. For example, in our template, DSS key 2 was set to prefix an 8 but since the "line" field was blank, the Yealink was trying to make the call using account 2.
We tested with a Yealink T52S and did not get the same result, it still used account 1 as it did in previous firmware versions.
The simple resolution was to include a "1" in the line field.
We reported this to our distributor to forward along to Yealink. Not sure if it will be addressed or not.

To answer the "why" question. The client uses trunks from 3 different providers depending on where they are calling and/or if a service provider is down (it is in a rural area that experiences frequent provider outages). The users know which provider to use in different scenarios but didn't want to memorize which prefix to use. So the prefix buttons add a digit based on the key they press which are labled with the different provider names. They then dial the number and 3CX's outgoing routing rules decide which trunk to use to process the call.