Re: [SWMP] TCP, UDP, and multicast: are they really equivalent?

Paul Aslin <> Fri, 07 September 2007 03:51 UTC

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Date: Thu, 6 Sep 2007 20:51:10 -0700 (PDT)
From: Paul Aslin <>
Subject: Re: [SWMP] TCP, UDP, and multicast: are they really equivalent?
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--- wrote:


> When I think about using swmp (or the enlarged version I
> proposed in 
> I 
> wonder whether I would ever use UDP or multicast for
> anything other than a 
> way to receive notifications as a result of a
> subscription.  Indeed, I 
> doubt I would want to receive all notifications via UDP. 
> Structural 
> changes, such as adding/dropping a node or
> adding/dropping a field are 
> probably sufficiently important that I would want to
> ensure reliable 
> delivery.  Indeed, some update notifications might occur
> infrequently or 
> be critical triggers and I would probably prefer to use
> TCP for them.
> The canonical example of where I really want UDP is
> updates about the 
> position of a moving object.  If I miss one update, I'll
> just wait for the 
> next one.  So long as the coding of the update is to
> declare the new 
> position rather than give me the delta, the improved
> speed is worth the 
> occasional loss.

Yeah position updates are a fine example of where data loss
isn't so much an issue. Probably should be some sort of
limiter applied to constantly updateing values, that more
an issue for programmers writing SWMP clients/servers/

I can see instances where programmers will be using SWMP
fields for information which lost data would be noticeable.
Say using a string to transfer chat text, or boolean states
of things like doors.

Perhaps we need to look at a flag, that can be set per
field/node as to the priority of updates to fields. In
other words, 'priority TRUE' would mean use TCP (or UDP
with some way of resending lost packets), FALSE would be
use UDP.

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