14 Aug
2004
14 Aug
'04
9:44 p.m.
From: "Steve Harris" <S.W.Harris(a)ecs.soton.ac.uk>
On Sat, Aug 14, 2004 at 10:07:06PM +0200, Benno
Senoner wrote:
No, the roundtrip latency is *at least* 100usecs (or whatever), the hardware
will keep re-transmitting until the packets get through.
In pratice people dont really demand hard realtime and it will be OK, but
the maximum time taken to transmit a UDP packet is unbounded, it uses
exponential backoff IIRC.
It is only unbounded if the network can't provide it, and if that is the case you
would lose the ethernet frame, which might be difficult to handle for something
like MIDI. Losing packets is not really hard real time either...
--ms
UDP also
has unbounded transit time. In practice its OK if you dont want
low latencies (just use RTP), but for low latency you really need one of
the non-IP ethernet protocols that can be relaibly used for audio.
I don't think raw ethernet will buy us anything over using UDP. These
few usecs less simply won't matter.
(but with ethernet you would have the disadvantage that you loose
routability)
On a 100Mbit network the round trip latency between hosts is about
100usecs so the one way latency of MIDI would be
about half of that. and that's form a MIDI point of view instantaneous
because over serial MIDI cable transmitting
a NOTE ON event (3 bytes) takes about 1.1msec which is 20 times slower
than transmitting it over an ethernet cable.