Call audio drops out during a call

[John14]

Hi,

One of our clients are experiencing intermittent call audio drops incoming as the external party can still hear the client but the client has no audio. Seems to range with when the audio drops and today audio dropped but a few seconds later audio came back. Its one way audio when this issue happens but the call is still connected. This happen 2 to 3 times a day so it's hard to replicate the issue and capture it.

I checked router details to make sure SIP ALG is disabled and port forwards are applied correctly. I made sure the internet bandwidth is not an issue by doing a connection test. Also completed the firewall check and was all fine.

Has anyone had this issue before and how did they resolve this? Any ideas what i can do?

thanks

 

[eddv123]

If I did have this issue, you have already suggested the two areas I would look at, SIP ALG and bandwidth. I assume you have checked your bandwidth calculations with: https://www.3cx.com/blog/docs/bandwidth-utilised-for-voip/

Have you managed to capture this issue using Wireshark, you could at the very least see the audio paths and get a better understanding of the issue.

 

[John14]

If I did have this issue, you have already suggested the two areas I would look at, SIP ALG and bandwidth. I assume you have checked your bandwidth calculations with: https://www.3cx.com/blog/docs/bandwidth-utilised-for-voip/

Have you managed to capture this issue using Wireshark, you could at the very least see the audio paths and get a better understanding of the issue.

Yes thats where i checked aswell. i can re evaluate the bandwidth just to make sure. Yeah it hard to get a capture on this issue as the issues doesn't seem to happen all time.

 

[cobaltit]

Doesn't sound like SIP ALG to me. Possibly bandwidth but you don't mention the internet connection speed/type. It sounds like a network issue with something inducing packet loss. Having outbound audio but no inbound audio is odd. I'd expect it to be the other way around with an asymmetric connection.

 

[John14]

Doesn't sound like SIP ALG to me. Possibly bandwidth but you don't mention the internet connection speed/type. It sounds like a network issue with something inducing packet loss. Having outbound audio but no inbound audio is odd. I'd expect it to be the other way around with an asymmetric connection.

I will re check the internet connection and see if i get a capture which will determine more info.

 

[drewt]

I had the same issue with a few clients, and the problem was being caused by to many switchs on the LAN, I upgraded the main switch to Netgear Smart Managed Plus Switch Series, jgs524pe and the work group switchs to gs305e. Netgear claims, and it seems to work, that these switchs are designed to be used together on the same network segment.

 

[John14]

I had the same issue with a few clients, and the problem was being caused by to many switchs on the LAN, I upgraded the main switch to Netgear Smart Managed Plus Switch Series, jgs524pe and the work group switchs to gs305e. Netgear claims, and it seems to work, that these switchs are designed to be used together on the same network segment.

They do have a switch at the office side which is where the base station for the cordless phones are connected. Right now i'm going to do some isolation test by connecting the station directly to the router and see if the calls drop after the change.

 

[eddv123]

Doesn't sound like SIP ALG to me.

I can see why you have said this as most related issues of SIP ALG are failed calls, registration issues (pre-call setup not during).

As you are aware SIP ALG inspects SIP traffic packets and modifies them in unexpected ways - unexpected being the definitive word here so I will always consider SIP ALG as I have experienced it working in different ways based on the vendor in use.

 

[eddv123]

@John14 another couple of points/questions:

Is your firewall doing packet inspection of your VoIP packets?

When you experience a drop, how is the CPU on your firewall - is it running heavily ?
If turned on and possible, your VoIP traffic should bypass your packet inspection.

Whilst on that subject you can (as a test) change your transport/traffic type on your IP handset from UDP to TCP, this would require to be done manually or via custom template however firewalls are more friendly to TCP traffic (due to TCP 3 way handshake) so it is a worth-while test.

Have you looked at your network setup specifically uplinks, for example regardless of bandwidth a congested uplink might cause issues for traffic if over-saturated or QoS is not in place.