Subject: [ippm] question on the reordering draft 09

From: Lei Liang <[email-masked]>
Date: Thu, 31 Mar 2005 17:28:30 +0100

Dear all,
  I am confused when reading the definition of the Type-P-Reordered
(part 3.3) when it talks about the reordered and in-order. It says:

  The value of Type-P-Reordered is defined as TRUE if s < NextExp (the
packet is reordered). 

   The value of Type-P-Reordered is defined as FALSE if s >= NextExp
   (the packet is in-order).

Then, as I understand it says a packet with sequence number S < the 
expected sequence number of the following packet should be reordered. 
the example can be given as a packet with sequence number of 3 and NextExp
of 4 is not in order???? it doesn't make sense.
or, it means that the sequence number s should be compared with the
NextExp number of the previous packet. then the example becomes as a packet 
with sequence number of 3 is not in order because the previous packet has a
metric parameter NextExp=4. this make sense.
Seems to me, the two explanations can both fit the definition. And I suggest
to stress the NextExp in the definition to clarify that it's belong to the 
previous packet rather than the current measured one.
cheers,
lei Liang

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From: Al Morton <[email-masked]>
Date: Thu, 31 Mar 2005 14:03:41 -0500

Lei,
Thanks for your comment, see below:

>    (the packet is in-order).

Both paragraphs above go on to say how to determine NextExp so that
the next arriving packet can be evaluated.

>of 4 is not in order???? it doesn't make sense.

Right, it doesn't make sense to calculate NextExp using the
packet that you are trying to evaluate. Whether or not NextExp is
re-calculated is conditioned on the outcome of the s to NextExp
comparison. So the sentences you left out above are very important.

>NextExp number of the previous packet.

Yes, that's what we said when introducing the "next expected" concept in
Section 3.0.

>then the example becomes as a packet

Will this help you (added second sentence)?

+  NextExp, the Next Expected Sequence number at the Destination,
    in units of messages. This stored value in NextExp is determined
    from a previously arriving packet.

Al