socket problem

[Gordon Wetzstein]

> > I have a problem with python sockets.
> > I broadcast a lot of pickled objects with socket. sendto(...), that
> > works.
> > Ireceive them on the other site with socket.recvfrom(16384)
> > The pickled objects are smaller (like 10000 bytes) than the max bytes.
> > 
> > The problem appears if I send too many pickled objects very quickly one
> > after another,
> > then I only receive a part of the sent objects.
> 
> As Jp Calderone pointed out, UDP is an unreliable protocol. Therefore,
> it *will* drop packets occasionally. Worse, it doesn't guarantee
> ordering of delivery of packets, meaning that your pickles could
> arrive all jumbled up and unusable.
> 
> You have three main choices to get around this problem.
> 
> 1. Use TCP, which guarantees delivery to the destination address once
> and only once, guarantees that packets will be received in the order
> in which they were sent. However, you can't broadcast with TCP: it's a
> point to point protocol.
> 
> 2. Implement your own guaranteed delivery protocol over UDP. This is
> usually done by assigning packets a sequence number as they are
> transmitted from the publisher. All consumers then keep track of the
> sequence numbers they receive, and re-request any packets they missed.
> Implementing your own such protocol can get quite tricky, depending on
> how complex your requirements.
> 
> 3. Use a pre-made, highly efficient python library which is custom
> designed for the job: spread. Spread is designed to solve all of the
> problems of reliable broadcasting over UDP, and gives you a wide range
> of options for how to balance efficiency versus reliability. And more
> importantly, it's  industrial-strength robust, stable and platform
> independent. Also, it's configurable to work with a wide range of
> network topologies. More info from
> 
> http://www.python.org/other/spread/
> 
> If I were you, I'd seriously consider spending an hour getting up and
> running with Spread: could be the most productive hour you'll spend in
> this area.
> 
> HTH,
> 
> -- 
> alan kennedy

thanks, i will try it.
gordon

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