Subject: Re: [linux-audio-dev] Introducing DMIDI
From: Dominique Fober (fober_AT_grame.fr)
Date: Wed Dec 19 2001 - 13:45:13 EET
There are some interesting ideas in these works and I would like to add a contribution to the discussion:
from my point of view, preserving the transmitted events scheduling with a maximum accuracy is important as this scheduling is part of the musical information itself. However, except considering that the protocol is intented to run on a fast local dedicated network, the transport latency will introduce an important time distortion. Therefore, a mecanism to compensate for the latency variation seems to me to be necessary.
Another point is the efficient use of the transmitted packets: sending one packet for each event is probably not the best solution. In this case and due to the underlying protocols overhead, the useful information part of a packet may become less than 10% of the packet size. Moreover, hardware layers such as Ethernet for example, often require a minimum packet size to operate correctly.
There are solutions to these problems: I've recently presented a paper at WedelMusic 2001 which take account of efficiency, scheduling and clock skew. Maybe, combining the different things may result in a improved solution.
You can temporarely get the paper at http://www.grame.fr/~fober/RTESP-Wedel.pdf
-df
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Dominique Fober <fober_AT_grame.fr>
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GRAME - Centre National de Creation Musicale -
9 rue du Garet 69001 Lyon France
tel:+33 (0)4 720 737 06 fax:+33 (0)4 720 737 01
http://www.grame.fr
>> But from what I understand of RTP the same
>> thing would/could happen if the protocols are switched.
>
>Yes, using RTP isn't about getting QoS for free --
>
>BTW, some LAD-folk may not be aware that sfront networking:
>
>http://www.cs.berkeley.edu/~lazzaro/nmp/index.html
>
>uses RTP for MIDI, we presented our Internet-Draft at IETF
>52 in Salt Lake a few weeks ago:
>
>http://www.ietf.org/internet-drafts/draft-lazzaro-avt-mwpp-midi-nmp-00.txt
>
>and it received a good reception -- the odds are good that
>it will become a working-group item for AVT. The bulk of
>this I-D describes how to use the information in RTP to
>handle lost and late packets gracefully in the context of
>network musical performance using MIDI ...
>
> --jl
>
>-------------------------------------------------------------------------
>John Lazzaro -- Research Specialist -- CS Division -- EECS -- UC Berkeley
>lazzaro [at] cs [dot] berkeley [dot] edu www.cs.berkeley.edu/~lazzaro
>-------------------------------------------------------------------------
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