RE: DDP segment sequences for Untagged DDP message

Note: this is the second sending, it did not show after the first time
within 24 hours...

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, if they were merely
received in this order (they got flipped in route and were received out
of order, but sent in order), then the result would be a normal
delivery.

I am not certain I agree with Pat on the "optional" nature of checking
for errors that are not even mentioned in the specification.  I think
that if we have to list all of the checks that we DO NOT perform in the
specifications, then we have quite a bit of writing left to do.

That said, we should perhaps be a bit more clear about the rules on
Sending overlapped segments, or Sending Gaps.  I am definitely not in
favor of requiring the receiver to check for either case.  If we were to
add text to DDP for this I think it would say something like:

When sending an Untagged Message, the Sender MUST send data to each
offset within the target buffer only one time.

When sending an Untagged Message, the Sender MUST send a contiguous
stream of bytes to the destination buffer, starting at offset 0.

In my mind, we should allow the receiver to check for these conditions
only if these rules are made on the sender.

Paul R. Culley
HP Fellow
281-514-5543


-----Original Message-----
From: [email protected] [mailto:[email protected]] 
Sent: Friday, January 23, 2004 4:45 PM
To: Culley, Paul; [email protected]; [email protected]
Subject: RE: [rddp] DDP segment sequences for Untagged DDP message


My responses are marked pat

-----Original Message-----
From: Culley, Paul [mailto:[email protected]]
Sent: Friday, January 16, 2004 12:28 PM
To: Barry Reinhold; RDDP
Subject: RE: [rddp] DDP segment sequences for Untagged DDP message


Below...

Paul R. Culley
HP Fellow
281-514-5543


-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of
Barry Reinhold
Sent: Friday, January 16, 2004 1:09 PM
To: RDDP
Subject: [rddp] DDP segment sequences for Untagged DDP message



So, is there agreement, for the sequences that follow, that the
specified "result" given below is the correct (and desired?) behavior as
defined by the 01 draft.

Untagged DDP Segment Sequences:

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

1. QN = 0, MSN = 1, MO = 100, L = 0, Payload = 100 bytes
2. QN = 0, MSN = 1, MO = 0,   L = 1, Payload = 100 bytes
Result: ULP sent Error type=Untagged Buffer Error, Error Code=Invalid MO
[prc] No, the receiver will place both segments, but inform the ULP that
only 100 bytes was delivered, ending at MO=99.  No error should be
detected or reported, unless the receiver's buffer was not large enough
to hold the second 100 bytes. [pat] Checking for the error of last
segment not containing highest MO is optional. Both behaviors above
would be valid responses.

1. QN = 0, MSN = 1, MO = 0, L = 0, Payload = 100 bytes
2. QN = 0, MSN = 1, MO = 0, L = 1, Payload = 100 bytes
Result: DDP Message (bytes 0-100) is delivered to ULP
[prc] yes, but it is not certain which segment ends up in the buffer, it
won't matter unless the two payloads are different. [pat] agree. 

1. QN = 0, MSN = 1, MO = 000, L = 0, Payload = 100 bytes
2. QN = 0, MSN = 1, MO = 200, L = 1, Payload = 100 bytes
Result: DDP Message (bytes 0-300) is delivered to ULP
[prc] yes, but the middle 100 will contain unknown values (probably what
they had before the buffer went through DDP). [pat] There are two valid
behaviors. The receiver may deliver the message as above or it may be
checking and report an error.

1. QN = 0, MSN = 1, MO = 300, L = 1, Payload = 100 bytes
Result: DDP Message (bytes 0-400) is delivered to ULP
(This is based on wording in 6.3, MO field. Note that the second
sentence simply says that the MO "that references the first octet MUST
be set to zero", not that a segment having a zero MO is required) [prc]
yes, but first 300 is unknown [pat] Again the receiver is allowed to
deliver or to report an error.

1. QN = 0, MSN = 1, MO = 100, L = 0, Payload = 100 bytes
2. QN = 0, MSN = 1, MO = 000, L = 1, Payload = 0 bytes
Result: ULP sent Error type=Untagged Buffer Error, Error Code = Invalid
MO (There is ambiguity between 6.1 L bit field description ( Segment w/
L bit set must have highest MO), and 9.1 (implies that for non-zero
length segments the header fields are not validated.) [prc] no, at least
not because of a protocol error.  There is only an error if the buffer
limits as defined by the ULP is exceeded.  You should get an indication
that a zero length message was delivered. [pat] The ambiguity you point
out is probably an error. The MUST on checking Untagged DDP segments
required that they be validated before placement. A zero length segment
isn't placed so the MUST didn't apply to it. There probably should be a
statement about checking the fields before delivery of zero length
untagged messages or zero length segments with the L bit set. Also even
if that statement is added, this is another case where the receiver is
allowed to deliver or report an error.

1. QN = 0, MSN = 1, MO = 000, L = 0, Payload = 100 bytes
2. QN = 0, MSN = 1, MO = 100, L = 1, Payload = 0 bytes
Result: DDP Message (bytes 0 - 100) is delivered to ULP
[prc] yes
[pat] yes. Note that this is another case where there should be a
requirement that the zero length segment header values be checked before
delivery.

1. QN = 0, MSN = 1, MO = 100, L = 1, Payload = 0 bytes
Result: DDP Message (bytes 0 - 100) id delivered to ULP. 
[prc], yes, but with unknown data values.
[pat] May deliver the message or may scoreboard and report an error.

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



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