> > > room or the header?? You can't fragment UDP so, as I understand it, you
> > > should never be able to send more than 1480 bytes on UDP. Or am I missing
> > > something?? Have the Specs changed? Can you now blast through anything??
> >
> > What do you mean ? Fragmentation is done at the IP layer ... so why does
> > this have anything to do with UDP ? Did I miss something here ?
>
> Well when I started in "Networking" about a thousand years ago when we
> used puffs of smoke for communication, a "Datagram" was a single packet
> of information which was not guaranteed to go anywhere nor was it
> guaranteed to arrive in the correct order. Datagrams came in two types
> inband, and out-of-band. You would send out-of-band datagrams for
> signaling. Data would go in-band. UDP (Unix Datagram Protocol) are
> (were) datagrams with an IP Header. If the IP "layer" now allows one
hmm this is all still true, at least it was last semester...
> to fragment, i.e., use datagrams that no longer consist of a single
> packet, then the whole reason for using datagrams has disappeared.
this confuses me, what about fragmentation removes the whole reason for
using datagrams. IP itself is a datagram, and must be able to be
fragmented. Fragmentation is necessary to allow larger packets to
travel over networks with smaller MTUs. So unless you are using something
with MTU discovery, or a homogenous network, it is always possible that
you are always going to need to use fragmentation. I understood (was
taught) that datagrams were connectionless and unreliable. Nothing was
ever mentioned that they had to stay as complete units, and could not be
broken up and put back together at the other end...
-chris
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Christopher Rogers Stevens Institute of Technology
Email:gandalf@pobox.com
HomePage http://stute.jacobus.stevens-tech.edu/~gandalf
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