Re: DDP segment sequences for Untagged DDP message

On Jan 27, 2004, at 8:01 AM, Culley, Paul wrote:

> OK, I realize that I missed a small point; in the first case below
>
>   1. QN = 0, MSN = 1, MO = 100 L = 1 Payload = 100 bytes
>   2. QN = 0, MSN = 1, MO = 0   L = 0 Payload = 100 bytes
>   Result: DDP Message (bytes 0-200) is delivered to ULP
>   [prc] yes
>   [pat]DDP message (bytes 0-200) occurs after 1.
>      2 will cause an invalid MSN error
>
> I was thinking of TCP segments as they arrive at the receiver, not as
> sent at the transmitter.  If the example was sent in this order, I 
> agree
> that an invalid MSN error is the correct answer,

The MSN is invalid, but the receiver is not obligated to catch it.

If DDP-Segment 2 is placed *before* DDP-Segment 1 is completed, then
no error will be detected. Both the MO and MSN are in range. The
100 bytes will be placed.

This obviously can occur if DDP-Segment 2 arrives before DDP-Segment 1.
But it can also occur if they arrive in order and the receiver
pipelines processing of DDP-Segments. Remember that all implications
of out-of-order processing hold no matter what the reason for the
out-of-order processing is. The packets do not have to have been
in the "wrong order" on the wire for out-of-order processing
to occur.

Similarly, the fact that MSN 17 invalidated STag 504 does not
guarantee that use of STag 504 in a tagged message that is
latter in the LLP stream will be flagged as an error. Invalidation
is only guaranteed by the time it is reported to the Data Sink ULP.




-- 
Caitlin Bestler - [email protected] - http://asomi.com/