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Lost audio when answering a call between two T54W phones
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ash Offline
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Post: #1
Lost audio when answering a call between two T54W phones
We've been deploying the Yealink T54W's lately and have been receiving a lot of complaints that when a call is answered the start of the call is not heard.

We have been able to reproduce this in a lab environment using 2 x T54W and doing the following:
  • Call from T54W to another T54W answering and saying 1, 2, 3, 4.
  • On each occasion we hear 2 or above, never 1

Doing the above, we are using G729, PCMA, PCMU codecs.

If we remove G729, PCMA, PCMU and only have G722 then you will always hear 1.

We have also tested the same scenario between two T42S phones and always 1 is heard so no dropped audio.

The other test we did was to go from a T54W to a T42S and 1 is also heard, so it only appears to be an issue between two T54W, or at least this is the most reproducible combination.
08-02-2019 07:43 AM
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complex1 Offline
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Post: #2
RE: Lost audio when answering a call between two T54W phones
(08-02-2019 07:43 AM)ash Wrote:  We've been deploying the Yealink T54W's lately and have been receiving a lot of complaints that when a call is answered the start of the call is not heard.

We have been able to reproduce this in a lab environment using 2 x T54W and doing the following:
  • Call from T54W to another T54W answering and saying 1, 2, 3, 4.
  • On each occasion we hear 2 or above, never 1

Doing the above, we are using G729, PCMA, PCMU codecs.

If we remove G729, PCMA, PCMU and only have G722 then you will always hear 1.

We have also tested the same scenario between two T42S phones and always 1 is heard so no dropped audio.

The other test we did was to go from a T54W to a T42S and 1 is also heard, so it only appears to be an issue between two T54W, or at least this is the most reproducible combination.

Hi,

In your test I miss 1 test... a call from a T42S to T54W.

Please try the T54W to T54W test again but now use codec PCMA or PCMU only and see if it happens again?

BTW: do you make use of a PBX?

Best regards,
Frank.

I'm Dutch, not English. Sorry for my imperfect grammar.
08-02-2019 06:08 PM
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jolouis Offline
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Post: #3
RE: Lost audio when answering a call between two T54W phones
Also are you running the T54W over wireless or on a wired connection?

I have a T53W, T54W and T57W here at my disposal so if you give me details I can test and try to investigate also.
08-02-2019 08:55 PM
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ash Offline
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Post: #4
RE: Lost audio when answering a call between two T54W phones
(08-02-2019 06:08 PM)complex1 Wrote:  Hi,

In your test I miss 1 test... a call from a T42S to T54W.

Please try the T54W to T54W test again but now use codec PCMA or PCMU only and see if it happens again?

BTW: do you make use of a PBX?

We can reproduce the issue using a T54W to T54W using G729, PCMA, PCMU, if you answer and count 1, 2, 3 you will hear 2 or above. Using a G722 you always hear 1.

Worth noting in the earpiece you can also tell the RTP hasn't established yet either.

If using a T54W and a T42S all codecs work, you will always hear "1". This seems to point me in the direction of a T5X issue.

All tests performed using Ethernet, have tried PoE and Power Supplies.

The PBX is FreeSWITCH 1.8 and we've also tried 1.6 to ensure it isn't anything on FreeSWITCH.

@Yealink - The latest firmware was released in April, is there a T5X SIP BETA firmware I can get access to and see if it is a bug that has been addressed.

(08-02-2019 08:55 PM)jolouis Wrote:  Also are you running the T54W over wireless or on a wired connection?

I have a T53W, T54W and T57W here at my disposal so if you give me details I can test and try to investigate also.

I can PM details to our servers if you like for testing but if you were to do the following my theory is you should be able to reproduce:

- 2 x T54W running firmware T54W-96.84.0.30.rom
- Factory reset the phones and setup the basics to register to a PBX
- Remove all Codecs and have G729 as the only listed codec
- Dial from Extension A to B, Answer B and say 1 2 3 4 and see if you hear 1

The configuration we are using is this:

- PBX is hosted on a public IP in an external data centre
- The two test phones are behind a NAT router connecting to the PBX on the public IP

I will try the same test today using a PBX on the same network segment as the phones just to confirm it isn't a NAT based issue, but as we don't appear to see the issue on T4X, T3X, T2X phones I don't think this will be the issue.
(This post was last modified: 08-03-2019 01:47 AM by ash.)
08-03-2019 01:39 AM
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ash Offline
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Post: #5
RE: Lost audio when answering a call between two T54W phones
Have now tested with the PABX on the same network segment as the IP phones and there is still a delay when answering the ringing phone.

With G722 I've noticed you can sometimes get it to miss the start of the answered call, but not as much as G729, PCMA/U.

Curious to know if anyone else is seeing this as well.
08-03-2019 08:53 AM
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sam_at_url Offline
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Post: #6
RE: Lost audio when answering a call between two T54W phones
As per the OP's scenario, I have been able to reproduce the bug calling between two T54W phones using an Asterisk 13-based server with PJSIP.

At least this potentially eliminates the voice switch platform as the cause.

Regards,

Sam
URL Networks Pty Ltd
08-04-2019 11:14 AM
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ash Offline
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Post: #7
RE: Lost audio when answering a call between two T54W phones
Hi Team,

Any update on this?
08-07-2019 06:44 AM
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