We browse websites using an HTTP proxy; there's no direct internet access. The only VoIP program that works out-of-the-box in our network is Skype and it's using that proxy too.
For example, I want to talk to someone who's using Linphone. Is it possible? Maybe through some web site.
To date, there's no good SIP implementation that supports TCP, so I stuck with UDP. Even if there was, others still use UDP
We have a functional socks5 proxy with UDP bind, but there's no SIP software that supports it.
On Linux it is theoretically possible to use
It is also possible to write my own SIP proxy with socks5 UDP bind support and run it in our LAN.
You can use Linphone from inside web browsers:
To install it under Firefox you need to go to LinphoneWeb and allow Firefox to automatically install the extension. Since this Linphone browser plug-in operates from within the web browser, I expect that it will respect any proxy settings that the browser itself honors.
Linphone supports TCP, but it actually depends on the SIP provider. Try Linphone's own SIP service. If Linphone is configured correctly, it supports both UDP and TLS (and most probably TCP).