Subject: Re: [linux-audio-dev] Introducing DMIDI
From: Phil Kerr (phil_AT_plus24.com)
Date: Fri Dec 21 2001 - 20:53:40 EET
Hi list,
Nice discussion. I've been AFK over the last few days and i'm catching up
here.
DMDI requires a higher bandwidth than MIDI. Cat 5 has higher throughput than
bell wire. The packetization of DMIDI can be very efficient. When receiving
MIDI notes from an interface DMIDI has to introduce it to the network. This
high header/payload ratio for one byte is as bad as it gets, yet the network
loading is still way within the limits for a 10mb network. If you send
complete MIDI control sequences or sysex messages within one DMIDI packet the
header/payload ratio will probably out strain the MIDI hardware interface.
It would be interesting to compare this limit of throughput from an 8k
DMIDI packet on different cards.
RTP provides far greater control in the delivery of packets. Yes, but it's a
pig to implement easily. DMIDI relies on a well set-up local network to work
correctly. Turn off ARP broadcasts, don't run NFS/Samba. Treat your network
like audio cable and DMIDI will work fine. MWPP is a fantastic protocol for
broadcasting over public networks with reliability but it's not been designed
from MIDI hardware up. It's roots lie in MPEG4 and is an extension to an
AV protocol. DMIDI's implementation is far easier to program, so developing
applications is far easier.
The risk of packet loss will be an issue with both protocols, accept it.
Regardless of what recovery methods are used there will always be a risk of
packet loss. I can't think of any AV protocol, that attempts packet recovery
so why do you need it on a private lan? MWPP type reliability could be
achieved with DMIDI but to do so would duplicate MWPP. DMIDI is a private lan
protocol and MWPP is best used for public broadcasts. They are focusing on two
separate set's of users.
Now, the only way to move things forward is to start developing applications
using both protocols. The most important thing is to get some MIDI
applications out running on Linux. I've written some code to demonstrate
DMIDI, someone write the same for MWPP, and lets get coding.
Phil
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