Log In

Come Join Us!

Are you a
Computer / IT professional?
Join Tek-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Tek-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Distorted audio

Distorted audio

Distorted audio


I have a strange issue.
A lot of outgoing calls with distorted audio.
Sip trunk involved.

We captured all the packets of a faulty call via a mirrorport on a phone.
Playing the audio stream in Wireshark there are no issues. Jitter, delay etc no problems.

I hope someone can point me into the right direction to figure it out.

Thanks in advance,


RE: Distorted audio

If ypu can verify audio is clean going out, trouble lies beyond MCD, MBG and in the carrier network or sip provider IMHO

RE: Distorted audio


Outgoing call, but incomming audio stream is clean when we playback, but for the user on the Mtel phone it's very bad.


RE: Distorted audio

Do you have QoS on the network?
If so, can you check PCAP trace to see if the packets are marked correctly

Is there an MBG involved?
If so run trace on MBG and verify if quality degrades before or after the MBG

Is the SIP trunk over the net or private circuit?

Clever men learns what Wise men shares!

RE: Distorted audio


First i want to thank you for replying.

QoS is configured correctly.

Yes there is a MBG involved.
Sip trunk is connected to the MBG.

When we do a packet trace on the mirrorport on the back of the phone it's all fine.
We have connected also a phone on a TW MBG. We can reproduce it.
We recorded de audio stream on the phone itself and we used our smartphone to record the phone itself.
On the phone robotic sounds, playback in Wireshark everything is fine.

This is so strange.

SIP trunk is connected on a Private Circuit.

For testing we have programmed a 2nd siptrunk(over the net)
We selected 5 phones. Those are using this new trunk for outgoing cals.

Still waiting for results


RE: Distorted audio

Hi Bigsin

Wireshark application is designed in such away that it re-aligns the packets which most times gives you the false audio playback.
I do not rely on the actual audio, you need to look in the packets.

If SIP trunk is anchored on the MBG, then you can pull the trace straight from the MBG itself.
At least this way you will be able to see the difference in the internal and external traffic.

You mentioned QoS is configure correctly, but my questions is are the packets marked correctly - signalling and RTP?

Clever men learns what Wise men shares!

RE: Distorted audio

Capture on the MBG for both incoming and outgoing call.
Compare SDP of the good and the bad.
Having problems with outgoing calls only rules out the phone hardware and configuration.
Could be a difference in routing.

RE: Distorted audio

John Keri

Appears to be a phone hardware issue on 53xx series(52xx not sure)
It's only occuring on Vodafone SIP trunks(Netherlands)

What s happening. In the RTP stream every now and then there is a faulty packet.
In the Packet traces this packet has a different (smaller) packetlength.

When this happening the phone is adapting to this packet length.
All correct packets will be processeced as it is a smaller packet.
Result: Distorted audio.

Firmware or higher should resolve this issue.

RE: Distorted audio

Hi Bigsin,

Thank you for the explanation.
Interesting problem. Considering that every SIP session negotiates the packetization rate in ms, it is not nice to send packets that do not adhere to that rate.
That said, considering the flexibility of SIP, devices can be made to support almost anything if the coding is correct.

In case this is specific to support an RFC, would appreciate a note of that for reference.

Just curious, why would this happen for outgoing calls only?



RE: Distorted audio

John Keri,

Why it's only happen on outgoing calls? I realy don't know.
Vodafone probably route their outgoing traffic via some very bead cheap routes.
It's looks like its only happen for specific countries, numbers.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Tek-Tips Forums free from inappropriate posts.
The Tek-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Tek-Tips forums is a member-only feature.

Click Here to join Tek-Tips and talk with other members! Already a Member? Login

Close Box

Join Tek-Tips® Today!

Join your peers on the Internet's largest technical computer professional community.
It's easy to join and it's free.

Here's Why Members Love Tek-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close