we encountered an issue with a customer using the default Jitsi (stable build 2.2 Mac or Windows or even Windows nightly build Jitsi 2.3.4951 Windows 7) when Jitsi tries to make a SIP call – Example:
The SIP-Proxy requires proxy authentication, so Jitsi tries to send a new INVITE containing the additional authentication parameters plus the SDP.
As the default settings in Jitsi include many codecs, the new INVITE SIP message contains now more than 1500 bytes (in that example 1552 bytes) so on the network layer only a frame of ca. 53 bytes is created. This package does not appear on the SIP-proxy side as SIP package - no further INVITE can be seen from the proxy, the call setup fails (Jitsi tries to resend the INVITE however the problem of size stays the same) .
1. change to TCP protocol (not preferred)
2. or disable some codecs (overwriting global codec settings) to reduce the size of the SDP so that it fits in one single MTU frame
Why an issue?
There is no easy way for a service provider who usually does not have access to the user's client to find the cause of the problem as the "lost" SIP messages cannot be traced on the SIP proxy side.
Additionally there is no warning for the Jitsi user that the message size exceeds standard network settings – normal users will never find the cause of the problem as they are trusting the standard setup of Jitsi.
Possible solutions: Either a proper warning (e.g. reduce number of codecs), changing the default settings for selected codecs or an active handling of the SDP container to adapt to message sizes.