[linux-audio-dev] ethernet vs serial MIDI again ...

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Subject: [linux-audio-dev] ethernet vs serial MIDI again ...
From: Benno Senoner (sbenno_AT_gardena.net)
Date: pe tammi  21 2000 - 09:26:51 EST


On Thu, 20 Jan 2000, jfm3 wrote:
> Dan Hollis wrote:
>
> > On Thu, 20 Jan 2000, jfm3 wrote:
> > > 10/100baseT doesn't make a good real time control protocol physical layer. It's
> > > not "real time" enough.
> >
> > And 38400 baud aysnc serial is? Boggle.
>
> Don't think about throughput, think about latency. When I send a message out on a
> MIDI cable, I have 100% certainty of when it will arive at its destination(s) within
> constant bounded tolerances (1 ms.). Similar claims can not be made of ethernet.
>
> Not that the limitations of MIDI don't bite me daily, but ethernet seems a lot like
> the wrong tool for the job.
>
> (jfm3)

I am not an ethernet expert, but assume that you run 10Mbit (or 100Mbit) through
a switch, which eliminates the collisions.

Of course if there is a trasmission error or packet loss, this packet will be
delayed and retransmitted.
Anyone who knows how much msecs this will take ?

Date can be lost on a serial cable too especially on long distances.

So my thoughts are the following:
on serial MIDI if you loose a byte (or a transmission error occurs) it can do
some damage due to potential misinterpretation of the sucessive data.

On ethernet using TCP the data will just arrive to destination in a reliable
fashion, the only problem could be a little delay in the case of a packet loss
or data transmission error.

what is the packet error rate on a switched ethernet network in case of using
decent equipement (especially cable).

I think this error rate is so low that we can assume the channel is virtually
error free, therefore NO NASTY DELAYS.

On ethernet you can even use optical fibers to achieve up to 2000 meters at
100Mbit.

As long as there are no packet collisions or transmit errors, ethernet
can be regarded as a realtime transmission medium.

I don't think that if you connect 2 musical instruments via ethernet, you are
doing large FTPs on the same bus-network during a live concert performance.

It's just like you have to avoid do run the defragmenter on your HD while
recording your 32 tracks with Cubase on windows.

Therefore my only remaining concerns are the packet-loss rate on a switched
network, but I think that for pratical purposes, it doesn't have any influence
on real-world performance.

any thoughts ?

Benno.
 


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