Re: new HW/SW trend?

[Kim Flint <kflint@loopers-delight.com>]

At 12:28 PM 1/21/2003, Jon Wagner wrote:
> > I've been wondering if manufacturers would move more towards "real"
>networking, ie: Ethernet.  With Gigabit ethernet hardware chips coming 
>down
>in price, giving bandwidth to spare, I'm wondering why manufacturers 
>haven't
>moved in that direction.
> >
>
>Me too. ethernet seems so obvious - its been around for a long time and 
>its
>not going anywhere anytime soon, and bandwidth is not a problem at all.  I
>wonder, is there a problem with variable (unpredictable) latency of 
>ethernet
>used for with audio stuff?

Ethernet is a horrible choice for networking realtime audio and other 
multimedia data for exactly the reason you suspect. The latencies can be 
quite large and unpredictable. Ethernet arbitrates the network at the 
hardware level with collision detection mechanisms and random back-off 
times, which means there is no way to guarantee a specific time when your 
message will arrive. TCP/IP at the higher layers makes this worse. The 
whole network is designed with the goal of getting the data there reliably 
and intact, not getting it there at a guaranteed time. You have to do a 
lot 
of buffering to overcome this, which makes real-time usage a major problem.

It is even worse for control data streams like MIDI. Can you imagine 
trying 
to play drums where the sounds you trigger are shifting variably by 
+/-50ms 
or more? Even shifting by 10ms would make it impossible to play a groove 
with a laid back feel vs on top of the beat. For that type of application 
a 
network that guarantees latency is even more critical.

(Long ago I worked on the zipi project, where we sought to solve this 
issue. we developed a token passing network similar to the type of thing 
used for "mission critical" control applications like factory automation 
and space launches. A good idea, but too much of a niche to get the 
momentum for it to survive.)

For these reasons, Ethernet was long ago discarded by the AES as an option 
for digital audio networks. 1394 (now called by apple's name Firewire) was 
designed from the beginning to handle media and control data streams, and 
is a much better choice. This is why you see all the audio companies 
adopting it (finally), and why camcorders and other video devices use it 
as 
well. Unlike something like zipi, it has wide enough usage and backing to 
really survive.

kim


______________________________________________________________________
Kim Flint                     | Looper's Delight
kflint@loopers-delight.com    | http://www.loopers-delight.com