--- "Perry E. Metzger" <perry@piermont.com> wrote:
> 
> Ali Khayam <ali_khayam@yahoo.com> writes:
> > Setting the checksum to zero means not performing
> any
> > checksum i.e. not even the header. But, not
> > checksumming the header is totally absurd because
> you
> > might end up processing a packet meant for someone
> > else.
> 
> Not very likely. In fact, it is so unlikely in a
> modern network that
> IPv6 eliminated header checksums entirely, deciding
> they weren't worth
> the bother.

True, but one of the major driving factors for this
decision was the presence of a checksumming capability
in the transport layer.

> If one insists, though, it is trivial to include a
> UDP header checksum
> in the data portion if you want. It will be static
> so you only have to
> compute it once. You can just shove it in the first
> couple of bytes of
> the data portion of the packet and the receiver
> could check that it
> showed up. Big Deal.

The "Big Deal" here is the incorporation of
prioritized traffic e.g. for MPEG transmission you
would like to perform a complete checksum on the
I-frames while checksumming only the header of the P-
and B-frames. Such capability can not achieved with
the static checksumming technique that you mentioned.

 
> > And UDP Lite is always used in combination with a
> variation of the
> > Link Layer Protocol.
> 
> In real networks, you're never going to have control
> like that over
> the link layer.

Its just a matter of turning the checksum capability
on/off. I am not an expert on that but it sure doesnt
sound very far fetched.

> 
> > UDP Lite has shown a lot of promise for real-time
> multimedia
> > applications on wireless networks.
> 
> I'm very active in the IETF's transport area. I
> hadn't heard of this

I know that this protocol was once an Internet Draft
of IETF (The UDP Lite Protocol
<draft-larzon-udplite-01.txt> ). Maybe you will be
kind enough to check its current status for me.

> previously, and as I said, the functionality seems
> like for practical
> purposes it is already there -- not that I can see
> how one would
> rationally use it.

I can not see how this functionality can be achieved
without over-burdening the application layer
protocols.


  -- Ali


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