Re: [PWOT] Re: comment on latest draft-martini-l2circuit-encap-mpls-01.txt

RTP already addresses this issue.  See Appendix 1 in RFC 1889 for an
implementation suggestion for header validation through sequence
number sequencing.
							-- Steve

> At 04:34 PM 3/16/2001 -0500, you wrote:
> >Hello Luca,
> >
> >Sorry for the late comment, I didn't know of this draft until recently.
> >I see the addition of the control word and algorithm for handling
> >sequence numbers on send and receive side.
> >
> >It seems that sequence check on receive side does not handle the
> >wrap around correctly, i.e. finds the out-of-sequence little too late.
> >
> >For example if the max was 64,
> >
> >sender                   receiver's expected Seq
> >
> >62          ->           62, next: 62+1=63
> >64          ->           63, 64>=63 packet in order. Next: 64+1=1, wrapped
> >63          ->           1, 63>=1 packet in order. Next: 63+1=64
> >1           ->           64, 1 !>=64. packet out-of-order, drop, next:1+1=2
> >
> >As shown above, out-of-order packet already forwarded!
>
> In general with a circular sequence number space you need to include the
> concept of a 'window' - the maximum sequence number that is reasonable to
> receive. This got left out of the definition in the draft. My inclination
> would be to define the window to 1/2 the sequence space (it could be made
> arbitrarily smaller, but there may not be any point). So, in your example
> above:
> - 63 > 1 + window, so discard
> - 1 == 1, in sequence
>
>
>
>
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