Subject: [rddp] (no subject)

From: "Barry Reinhold" <[email-masked]>
Date: Thu, 8 Apr 2004 10:42:24 -0400

How would you expect a MPA receiver to handle an out of order TCP
segment with markers disabled and CRC off? Does it just buffer it until
the gap is filled?

Also, if CRCs are enabled and we are processing an out of order PDU
without markers, what is the behavioral expectation of a failed CRC
check? A matched CRC would be sufficient to determine FPDU alignment,
but a failed CRC appears only to say that you may not have FPDU
alignment. 

That is, if I created a test that produced a gap in the TCP sequence and
then sent an unaligned FPDU within a TCP segment, followed by the
missing information I would expect the receiver to: (1) Not drop the
connection, (2) Advance the ACK through the unaligned segment when the
missing information was sent.

Is this the correct understanding?

Barry Reinhold
Lamprey Networks
[email-masked]
(603) 868-8411

_______________________________________________
rddp mailing list
[email-masked]
https://www1.ietf.org/mailman/listinfo/rddp

---

From: "Carrier, John" <[email-masked]>
Date: Thu, 8 Apr 2004 15:55:07 -0700

Hi Barry,

FPDU alignment is a property of the TCP segment where the first byte of the FPDU follows the TCP header.  A valid FPDU CRC, however, does not guarantee FPDU alignment.  Thus, turning CRCs off is orthogonal to turning markers off.

If markers are disabled, an MPA receiver can only determine the start of the next FPDU from the length of the previous FPDU.  If a TCP segment is received out of order, the MPA receiver would have to buffer the segment until the gap is filled. 

--jc

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]]On 
> Behalf Of Barry
> Reinhold
> Sent: Thursday, April 08, 2004 7:42 AM
> To: RDDP
> Subject: [rddp] (no subject)
> 
>

---

From: "Teisberg, Robert" <[email-masked]>
Date: Thu, 8 Apr 2004 17:07:07 -0500

> segment with markers disabled and CRC off? Does it just 

Most likely.  It could also discard it.  Anything plain TCP can do is
allowed.

For what it's worth, if markers and CRCs are turned off, the
implementation is probably software MPA over MPA-unaware TCP.  A
survey of existing TCP implementations will give you a good idea what
to expect.

> Is this the correct understanding?

It's one possibility.

Depending on timing and the receiver's TCP implementation, there are
some potentially interesting alternatives:

(2a) Discard the out-of-order segment, and advance the ACK only through
the previously missing information (go-back-n).

(2b) and (2c) SACK, and otherwise behave as in either (2) or (2a).

I don't know how likely these are, but they're all legitimate.