Subject: RE: [PWE3] Regarding PW header's SeqNum field.

From: "Aanand, Siddharth" <[email-masked]>
Date: Mon, 19 Feb 2007 09:26:12 -0500

Ganesh,

I am not exactly sure why you need the cell sequence number but in any case
let us assume that you do, we know that a packet is either completely
delivered at the Egress PE or not. In that case can the egress PE not keep a
running count (on a per-flow basis) as it is extracting cells from the
concatenated packet?

Sidd

-----Original Message-----
From: D, Ganesh (Ganesh) [mailto:[email-masked]] 
Sent: Saturday, February 17, 2007 7:13 AM
To: [email-masked]
Subject: [PWE3] Regarding PW header's SeqNum field.

Hello All,
 
- The PW header's seq num is suppose to have sequence num of PW pkt's.On
the Egress side each pkt will have 16 bit seq num is incremented for
every pkt (  0 to 2^16 ).
- And on the Ingress side these pkts will be held in a buffer and the
seq num will help in reordering the pkt's if they got out of order while
traversing the PSN. And seq num will also help in abroving the PSN
jitter.
 
Here is a situation observing am dealing with,
 
- If the PWE solution should use the existing jitter buffer mechanism
already existing, then the pkt seq num should be converted to cell seq
num.
- The pkts contain cells. Lets say a PW is configured for
'CellConcatDepeth'. And let 'CellOffset' be the offset of the cell with
in this PW pkt ( first cell will have 'CellOffset' = 0, second cell will
have 'CellOffset' = 1, and so on till 'CellOffset' =
(CellConcatDepeth-1) ).  
- Then the cell seq num can be easily calculated as 'cell seq num' =
(CellConcatDepth*PktSeqNum) + (CellOffset).
- But the problem is PW Pkt may contain number of cells less than
CellConcatDepth. In that case above formula will have holes in the
cellSeqNum.
- The above problem can be solved if, PW header contains cellSeqNum of
cell at CellOffset = ZERO ( let me call it cell0_seqNum ). Then 'cell
seq num' =  cell0_seqNum + CellOffset    .
 
Can any body please tell me how can i carry this extra information? or
shall pkt seq num be replaced with cell0_seqNum ( but that's against the
draft ).
Can any body through some light at other way of solving this problem.
 
Thanks in advance
Ganesh.D 

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---

From: Stewart Bryant <[email-masked]>
Date: Mon, 19 Feb 2007 15:23:56 +0000

This looks rather like a proprietry buffer management
design issue rather than a PWE3 protocol issue.

- Stewart