Re: [dcp] Protocol Version number

[Mark Handley <mjh@icir.org>]

>I noticed the DCP header portion is mising  a protocol version field,
>though section 4.6 makes reference
>to "The version of DCCP".  Can we add a version field in the protocol
>header?

It seems to be a waste of bits.  There are a number of ways to evolve
protocols.  

 - If the packet formats need to change enough so that receivers or
   middleboxes would be confused, then you might as well use a different
   IP protocol number.  

 - If the change is minor, then it's most easily done in a backward
   compatible way by adding a feature that is negotiated.  

 - If the change is not so minor, a non-negotiable feature could be
   sent in the DCP request.

 - Finally, there are four bits in the DCP common header that are
   marked as MUST BE ZERO for this version of DCP.  If we decide at some
   future point that we really need a version number, between one and
   four of these bits can be designated as a version number field.

Neither TCP nor UDP has a version field.  I think time has shown this
to be a reasonable decision.

Cheers,
	Mark

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