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Noise in audio stream over VPN and RDP

Dennis Kirschner

Hello,

we have problems with the following scenario:

In the company there is a remote desktop server and a VoIP phone system (Starface). The HomeOffice users connect with the Sophos Connect Client (SSL VPN) to our Sophos XGS116w (SFOS 18.5.2 MR-2-Build380). The VoIP client of the PBX is installed on the remote desktop server. The audio stream is then tunneled to the terminal server via RDP.
In this constellation, the person who was called by this user hears "robot noises" again and again at random intervals (between 10 seconds and 10 minutes).

These problems do not occur in the company, although the users there also work in the same way on the remote desktop server.
If the user installs the VoIP client on his local PC, these problems do not occur either.
The problem must therefore be an interaction between Sophos and the audio stream via RDP.

We have already tried the following:

- system system_modules sip unload
- set advanced-firewall udp-timeout-stream 150
- set ips sip_preproc disable
- set vpn conn-remove-tunnel-up disable

We have also already turned IPS off completely with no improvement.

Does anyone have an idea how we can solve this?

Thank you.

Best Regards

Dennis



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  • 0

    because RDP is a secure protocol, which requires a cert exchange between the client and the RDP server the firewall will not see the SIP session and RTP stream transparently, so those system module settings will not be impacting any of this. The best way to handle this is to make sure the SSL VPN client is getting enough bandwidth. Also there is a good chance that the terminal server might be compressing the RTP stream when it is sending it across the IP to the thin clients and if this mechanism is not happening or if this mechanism is being impacted because of traversing across  a tunnel. When you say you turned off IPS completely did you stop the service ? or did you disable it on the rule only ?

  • 0 in reply to kranthi yadlapudi

    Hello,

    I will carry out the firmware upgrade in the short term.

    But we were able to narrow down the problem a bit again:
    We have set up a direct NAT to the terminal server instead of the VPN, so that we could connect to the server without VPN for testing. The problem occurs there as well. I had the impression that it did not occur so often, however.

    We can therefore rule out VPN as the only cause.

    We deactivated IPS via the switch under IPS protection.

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  • 0 in reply to kranthi yadlapudi

    Hello,

    I will carry out the firmware upgrade in the short term.

    But we were able to narrow down the problem a bit again:
    We have set up a direct NAT to the terminal server instead of the VPN, so that we could connect to the server without VPN for testing. The problem occurs there as well. I had the impression that it did not occur so often, however.

    We can therefore rule out VPN as the only cause.

    We deactivated IPS via the switch under IPS protection.

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