Subject: ATM encap sequence number processing

From: "Yaakov Stein" <[email-masked]>
Date: Wed, 30 Oct 2002 18:47:19 +0200

I have two comments regarding 
section 4.1.2. "Processing the sequence number"
in the recently released draft-ietf-pwe3-atm-encap
document.

1) The following is stated 
  "If a packet passes the sequence number check, 
  or is in order then, it can be delivered immediately."
where in order is defined as
  "if the packet sequence number >= the expected sequence number"

This is contradiction with the later statement that 
reordering may be employed at the discretion of the receiver.

If the sequence number is > the expected sequence number
and this packet is shipped out, reordering is no longer
possible.

The wording should either read 
 "If a packet passes the sequence number check, 
  or is in order then, it MAY be delivered immediately."
where the MAY refers to the case that reordering is not
used.  Otherwise the condition could be changed to
  "if the packet sequence number equals the expected sequence number"

In addition, the following is stated
  "When an emulated VC is initially set up, the "expected sequence
   number" associated with it MUST be initialized to 1."
I assume that this means that the first sequence number transmitted
should also be set to one. This may raise security issues.
Perhaps it should be set to a random non-zero number.

Y(J)S