NOTE: this page detail the principle for Jami accounts. For SIP accounts, the SIP protocol is used.
When creating a call between two peers, Jami mainly uses known protocols such as ICE, SIP or TLS. However, to make it distributed, the process of creating a call is a bit different. To summarize, when someone wants to contact one of its contact, this is what they will do:
Once the contact is found, send a call request, announcing the known candidates (the ip of each network interfaces + relay addresses (TURN) + reflexives addresses (UPnP, public ones).
Wait for the response of the contact (they will respond their known addresses).
Negotiate the socket via ICE. In fact, two ICE sessions are negotiated. One (preferred) in TCP, one in UDP (as a fallback).
Then, the socket is encrypted in TLS (if TCP) or DTLS (if UDP).
The contact is now able to accept or decline the call. When they accept, a ICE transport (UDP only for now) is negotiated to create 4 new sockets for the medias (2 for audio, 2 for video).
The call is now alive!
Exchange ICE candidates
Everything really starts in jamiaccount.cpp (JamiAccount::startOutgoingCall). Once both ICE objects are ready and when the contact is found via the DHT, the call request for the contact is crafted. This request contains all the informations necessary for the remote ICE session defined by:
where callvid is a random number used to identify the call and blob contains two concatened ICE messages (IceTransport::packIceMsg in ice_transport.cpp) containing the password of the session, the ufrag and ICE candidates.) like:
0d04b9357c33834e7cf944bf0e367b42H6e6ca382 1 UDP 2130706431 2607:fad8:4:6:9eb6:d0ff:dead:c0de 14133 typ hostH42c1g477 1 UDP 2130706431 fe80::9eb6:d0ff:fee7:1412 14133 typ hostHc0a8027e 1 UDP 2130706431 192.168.0.123 34567 typ hostSc0a8027e 1 UDP 1694498815 X.X.X.X 32589 typ srflx0d04b9327c33834e7cf944bf0e367b47H6e6ca682 1 TCP 2130706431 2607:fad8:4:6:9eb6:d0ff:dead:c0de 50693 typ host tcptype passiveH6e6ca682 1 TCP 2130706431 2607:fad8:4:6:9eb6:d0ff:dead:c0de 9 typ host tcptype activeH42c1b577 1 TCP 2130706431 fe80::9eb6:d0ff:fee7:1412 50693 typ host tcptype passiveH42c1b577 1 TCP 2130706431 fe80::9eb6:d0ff:fee7:1412 9 typ host tcptype activeHc0a8007e 1 TCP 2130706431 192.168.0.123 42751 typ host tcptype passiveHc0a8007e 1 TCP 2130706431 192.168.0.123 9 typ host tcptype activeSc0a8007e 1 TCP 1694498815 X.X.X.X 42751 typ srflx tcptype passive
and is sent via the DHT in an encrypted message for the device to hash(callto:xxxxxx) where xxxxxx is the device id. The peer will answer at the exact same place (but encrypted for the sender device) its own dht::IceCandidates. See JamiAccount::replyToIncomingIceMsg for more details.
The ICE session is created both side when they have all the candidates (so for the sender, when the reply from the contact is received).
Pending calls are managed by JamiAccount::handlePendingCallList(), which first wait that the TCP negotiation finish (and if it fails, wait for the UDP one). The code for the ICE negotiation is mainly managed by pjproject but for Jami, the interesting part is located in ice_transport.cpp. Moreover, we add some important patches/features on top of pjproject not merged upstream for now (for example, ICE over TCP). These patches are present in contrib/src/pjproject.
Encrypt the control socket
Once the socket is created and managed by an IceTransport instance, it is then wrapped in a SipTransport corresponding to a TlsIceTransport. The main code is located into JamiAccount::handlePendingCall() and the wrapping is done into SipTransportBroker::getTlsIceTransport. Finally, our session is managed by TlsSession in daemon/src/security/tls_session.cpp and uses the GnuTLS library.
So, the control socket will be a TLS (1.3 if your and your peer gnutls version support it) if a TCP socket is negotiated. If a UDP socket is negotiated instead (due to firewall restrictions/problem in the negotiation/etc), the socket will use DTLS (still managed by the same parts).
The control socket is used to transmit SIP packets, like invites, custom messages (Jami sends the VCard of your profile on this socket at the start of the call, or the rotation of the camera), text messages.