|
|
|
|
Voice over IP
|
|
|
|
|
-------------
|
|
|
|
|
Matrix can also be used to set up VoIP calls. This is part of the core
|
|
|
|
|
specification, although is at a relatively early stage. Voice (and video) over
|
|
|
|
|
Matrix is built on the WebRTC 1.0 standard. Call events are sent to a room, like
|
|
|
|
|
any other event. This means that clients must only send call events to rooms
|
|
|
|
|
with exactly two participants as currently the WebRTC standard is based around
|
|
|
|
|
two-party communication.
|
|
|
|
|
|
|
|
|
|
{{voip_events}}
|
|
|
|
|
|
|
|
|
|
Message Exchange
|
|
|
|
|
~~~~~~~~~~~~~~~~
|
|
|
|
|
A call is set up with messages exchanged as follows:
|
|
|
|
|
|
|
|
|
|
::
|
|
|
|
|
|
|
|
|
|
Caller Callee
|
|
|
|
|
[Place Call]
|
|
|
|
|
m.call.invite ----------->
|
|
|
|
|
m.call.candidate -------->
|
|
|
|
|
[..candidates..] -------->
|
|
|
|
|
[Answers call]
|
|
|
|
|
<--------------- m.call.answer
|
|
|
|
|
[Call is active and ongoing]
|
|
|
|
|
<--------------- m.call.hangup
|
|
|
|
|
|
|
|
|
|
Or a rejected call:
|
|
|
|
|
|
|
|
|
|
::
|
|
|
|
|
|
|
|
|
|
Caller Callee
|
|
|
|
|
m.call.invite ------------>
|
|
|
|
|
m.call.candidate --------->
|
|
|
|
|
[..candidates..] --------->
|
|
|
|
|
[Rejects call]
|
|
|
|
|
<-------------- m.call.hangup
|
|
|
|
|
|
|
|
|
|
Calls are negotiated according to the WebRTC specification.
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Glare
|
|
|
|
|
~~~~~
|
|
|
|
|
This specification aims to address the problem of two users calling each other
|
|
|
|
|
at roughly the same time and their invites crossing on the wire. It is a far
|
|
|
|
|
better experience for the users if their calls are connected if it is clear
|
|
|
|
|
that their intention is to set up a call with one another.
|
|
|
|
|
|
|
|
|
|
In Matrix, calls are to rooms rather than users (even if those rooms may only
|
|
|
|
|
contain one other user) so we consider calls which are to the same room. The
|
|
|
|
|
rules for dealing with such a situation are as follows:
|
|
|
|
|
|
|
|
|
|
- If an invite to a room is received whilst the client is preparing to send an
|
|
|
|
|
invite to the same room, the client should cancel its outgoing call and
|
|
|
|
|
instead automatically accept the incoming call on behalf of the user.
|
|
|
|
|
- If an invite to a room is received after the client has sent an invite to
|
|
|
|
|
the same room and is waiting for a response, the client should perform a
|
|
|
|
|
lexicographical comparison of the call IDs of the two calls and use the
|
|
|
|
|
lesser of the two calls, aborting the greater. If the incoming call is the
|
|
|
|
|
lesser, the client should accept this call on behalf of the user.
|
|
|
|
|
|
|
|
|
|
The call setup should appear seamless to the user as if they had simply placed
|
|
|
|
|
a call and the other party had accepted. Thusly, any media stream that had been
|
|
|
|
|
setup for use on a call should be transferred and used for the call that
|
|
|
|
|
replaces it.
|
|
|
|
|
|
