Subject: RE: [rddp] Error code returns for DDP tagged buffer messages

From: "Shah, Hemal" <[email-masked]>
Date: Mon, 26 Apr 2004 12:25:21 -0700

Barry,

See my comments below embedded between <hvs> and </hvs>.

Hemal

-----Original Message-----
From: [email-masked] [mailto:[email-masked]] On Behalf Of
Barry Reinhold
Sent: Friday, April 23, 2004 12:22 PM
To: RDDP
Subject: [rddp] Error code returns for DDP tagged buffer messages

Clause 9.2 DDP Error Numbers provides the error codes "Invalid STag" and
"STag not associated with DDP Stream", but the language of the first
paragraph is not clear enough for me to understand the expectation for
the following:

<hvs>
For an "Invalid STag" memory access is not allowed at all. "STag not
associated with DDP Stream" means that the STag is valid but is not
associated with the DDP Stream on which the DDP Segment was received. In
other words, memory access using the STag is not allowed on this DDP
Stream. 
</hvs>

Is it the intent to require that a receiver delineate between "Invalid
STag" and "STag not associated with DDP Stream"? That is, if STag 10 was
valid on stream A but not on stream B, MUST the receiver return "STag
not associated with DDP Stream?" if a DDP Segment is received on stream
B with STag 10, or is "Invalid STag" acceptable.
<hvs> No. The receiver MUST return "STag not associated with DDP Stream"
in this case. </hvs>

This question also applies to delineating between "Invalid MSN - no
buffer available", and "Invalid MSN - MSN range is not valid". However,
this is a bit more difficult conceptually as Clause 9.1, item 5 states:

       The legal range is defined as being between the MSN value
assigned to
       the first available buffer for a specific QN and the MSN value 
       assigned to the last available buffer for a specific QN.

Which appears to tie "invalid MSN pretty closely to no buffer available.
<hvs>
Let us say QN has a queue length QLEN. So, at any given point [MSN1,
MSN2] represents the MSN range of the entries of the queue. Here,
MSN2-MSN1 = QLEN-1 (in modulo arithmetic). Let us say the number of
buffers posted on the queue at any given time is N (0 <= N <= QLEN).

So, for N > 0, if a MSN is not in [MSN1,MSN1+N-1] and MSN1 <= MSN <=
MSN2, then it is the condition "Invalid MSN - no buffer available". For
N=0, if MSN is in [MSN1, MSN2], then it is the condition ""Invalid MSN -
no buffer available".

If MSN is not in [MSN1,MSN2], then it is "Invalid MSN - MSN range not
valid" condition.
</hvs>  

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

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