RE: Potential data corruption in DDP with MSN protocol violation

Barry,

The receiver can detect this protocol error by keeping track of the next
MSN to be delivered. So, while delivering MSN=3, it can identify a hole
in the MSN. I agree with you that this case is not covered in the errors
section.

I would propose we add an error "Invalid MSN - gap in MSN" (type=0x2,
code=0x00) for Untagged buffer errors.

Thoughts?

Hemal 

-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of
Barry Reinhold
Sent: Friday, April 23, 2004 12:41 PM
To: RDDP
Subject: [rddp] Potential data corruption in DDP with MSN protocol
violation

Based on the current wording in ddp draft 02, clause 9 it appears that a
receiver can place and deliver a sequence of DDP messages that arrive
with sequence number MSN=1, MSN=3, MSN=4 if there is no gap in the LLP
stream sequence. This could only be generated by a protocol error on the
transmitting side. 
However, if the transmitter did indeed generate this sequence
incorrectly it is conceivable that the receiver would have old data in a
buffer associated with MSN=2 and deliver it to the ULP.

Although one does not in general like to have the receiver check for
protocol errors, this may be an area in which the wording of the
standard should be strengthened a bit, such that DDP messages can not be
delivered when there are holes in the MSN space.

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




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