One Way Speech

I’m experiencing intermittent one way audio (I can hear the other person, but they can’t hear me). I’d like to know the best way to troubleshoot this issue. I have WireShark set up and can mirror any port to my WS machine. Before I re-invent the wheel, I thought it might be a good idea to post this request to the forum. What steps should I take to troubleshoot this issue? Are there any articles that someone can point me to, or point out which port I should mirror and what I should be looking for in a WireShark trace. Right now I’m assuming it could be a piece of gear on my network, but don’t know.

Thanks in advance for any help that can be provided.

are both ends of the call internal (on the same network as the pbx)? with a bit more info about your environment it might be possible to make an intelligent guess as to the problem

Thanks for the response.
This is on external calls; One phone is connected to FreePBX and the other one is external to the network (its on PSTN).

Would anyone else have an idea as to how I can troubleshoot this?

Thanks for any help provided.

Hi Michael,

i don’t have a general method to trouble shoot this, but to my experience, those Problems are either a NAT Problem, especially, you have the other phone not in the local Network, or i also found sometime codec Problems causing those Problems.
That’s where I would look into first.
Hope i maybe could help.

Cheers, Niels

Make sure the extension NAT mode = Yes (force_rport,comedia)

Thanks very much for the responses. I will look into it. In the meantime I did find this article on the FreePBX Wiki that I think could be quite helpful:

Also, just as an FYI my cable modem / router is a Cisco DPC3825 DOCSIS 3.0 Gateway. Any advice on specific settings for this?

Thanks again for the help.

Be aware that many cable providers don’t like you using VOIP as it is competition, make sure that the modem and/or your provider is not obstructing/delaying your voip traffic. Use iax2 if you can . . .

the cisco docsis modems sometimes come with alg turned on. log into the router and turn it of or call the cable provider and have them do it for you

Also be careful with Cable service, as it often goes to pieces at about 4:20 pm when the kids get home and you are sharing your bandwidth with gamers and down-loaders :wink:

i guess i was assuming this person was using comcast business, not their residential service. i have never looked into how they do it, but business service does not suffer the same slow down effect that residental users experience.

Here’s an update. I did call Rogers and they are not delaying any VoIP traffic. My latest incident happened at 12:30pm, July 8, 2016 (hopefully network traffic on the Rogers side wasn’t that busy). I’ve now got the FreePBX server wired directly to the modem (by-passing my switch) and it’s in the DMZ (by-passing the router). I have the FreePBX Firewall on with “Responsive Firewall” enabled. Interestingly I have an Avaya IP Office phone plugged directly into the cable modem and VPN’d into my companies switch. It has horrible one way speech. I’m thinking that I may have a modem issue?
FYI, here are the latest speed tests:
Last Result:
Download Speed: 36006 kbps (4500.8 KB/sec transfer rate)
Upload Speed: 5558 kbps (694.8 KB/sec transfer rate)
Latency: 20 ms
Jitter: 2 ms
2016-07-09, 12:15:56 PM

As always, any feedback is greatly appreciated.

did you log into the cable router/modem and see if alg is turned on?


I contacted Rogers and they logged into the modem but are unable to turn off ALG. It appears the next step would be to buy a router, connect it to the modem and put the Rogers cable / router / modem into bridge mode.

Does that make sense?


what i would do is, if rogers allows it, but a new docsis modem (motorola surfboard is a recommendation) and return the rogers supplied one and then purchase your own router/firewall. i can assure you that will fix the problem. depending on your budget/expertise i would suggest putting in an edgemarc 4700 session border controller. it will allow you to do traffic shaping (among other things) so when you start viewing a video on your computer, your phone call voice quality does not go in the dumper. you can monitor MOS scores as well. i am sure others will give you plenty of opinions on routers as well but we have used edgemarc’s for years - in fact we will not provide hosted phone service if the customer does not agree to put one in (i just hate the phone call -'i have choppy voice"). i even use one at home

Thanks for the response.
Unfortunately, the cable / modem / router is mine. I wouldn’t be able to return it to Rogers. So… I’m thinking of buying the Ubiquity Edge Lite.

I don’t know if Rogers will sell me a Motorola Surfboard but I know they’ll sell me the latest Docsis (which apparently ALG can be turned off).

All this might not take place until August as I’ve got other commitments. In the meantime I can swing the analog phone back onto the PSTN line and keep the SIP trunk on the FreePBX system and continue experimenting with the features of FPBX.

Thanks for the advice and I’ll update this post with my findings.

I thought I would update the group, in case anyone else runs into a similar situation. I basically followed Bob’s advise; some what. I kept the Cisco DPC3825, and changed it from “router” mode to “bridge” mode. Then I installed a Ubiquiti Edge Lite Router with QOS enabled. I now don’t have the one way speech issue’s I was experiencing before. I have an Avaya phone VPN’d into my work switch and FreePBX going throught the same network without any issue’s. Unfortunately the wireless has been turned off, but I’ll be upgrading that in the future.
Thanks again for all the help. Very much appreciated.