[Spice-devel] spice udp support

[Sunny Shin]

I heard that iptv uses udp multicast, so I thought that performance might
be better if we use udp for video streaming. We can ignore missing and out
of order frames. Does it make sense?

I understand that we need tcp channels for all others such as input and
audio channels.

2016-02-02 23:03 GMT+09:00 Gerd Hoffmann <kraxel at redhat.com>:

> On Di, 2016-02-02 at 10:24 +0100, Christophe Fergeau wrote:
> > Hey,
> >
> > On Tue, Feb 02, 2016 at 06:10:28PM +0900, Sunny Shin wrote:
> > > I have a few questions about udp version of spice protocol.
> > >
> > > Is there a plan to support udp in spice protocol?
> > >
> > > If we support udp, what do we need to implement?
> > > Is it enough to change tcp channels to udp ones?
> >
> > Maybe that would be enough, maybe more changes would be needed, I cannot
> > exactly tell you. My main worries with UDP would be packet drops as
> > there is nothing guaranteeing you that the packets you send will arrive
> > at all to the other end of the connexion.
>
> That is exactly the problem.  Packets may get dropped.  Packets may also
> arrive out-of-order.  So using UDP is fine if loosing data is fine[1].
>
> For spice this is largely not ok.  Maybe for the audio channel, if you
> are willing to accept sound dropouts in case of packet loss.  Loosing
> display channel messages will lead to rendering gliches due to missing
> data and render tree inconsistencies.  Not cool.  Loosing input channel
> messages may mess up the keyboard state such as keys being stuck due do
> keyup messages being lost.  That is even less funny.  Webdav file
> sharing corrupting your files?  Have the backups ready!
>
> cheers,
>   Gerd
>
> [1] In theory one could implement some scheme to track packet
>     status, resend lost packets etc to fix this.  In practice
>     the better answer to that is "use TCP" which does exactly
>     that.  And keep in mind that the TCP algorithms in todays
>     OS kernels are the result of decades of network protocol
>     research.  Coming up with an implementation which matches
>     TCP in performance certainly is not trivial.
>
>
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