Subject: Comments on draft-malis-pwe3-sonet-03

From: Akiva Sadovski <[email-masked]>
Date: Sun, 30 Jun 2002 10:38:45 +0200

Andy,

1) In section 5.2 "CEP Header" there is Note 1:
"Implementations that choose to support programmable payload 
   lengths SHOULD support payloads that are an integer multiple of 8 
   bytes." Further, in section 9.1 the draft states "...EPAR implementations
SHOULD 
   support a minimum payload length of 783/3 or 261 bytes" . IMHO, the draft
will be more
  consistent with one of these SHOULDs dropped. As for me,  the statement of
section 
  9.1 based on SONET/SDH ptr management principles better fits the draft
than that of 5.2
  based on ... maybe some implementation experience.

2) 6.2 Description of Normal CEP Operation : "The jitter buffer SHOULD be
adjustable in length to 
   account for varying network delay behavior. " It is not clear from the
text of the draft whether the 
   jitter buffer size can be changed during normal PW operation, or it is
preconfigured
   during PW setup  (taking into account nework behavior, etc) and cannot be
changed during PW operation.

3) In 6.4 : "If a CEP de-packetizer supports re-ordering, any packet
received before its play 
   out time will still be considered valid". Not _any_ ; it depends on the
reordering buffer 
   (same as jitter buffer) length.

4) More from 6.4: "However, if the jitter buffer is empty or the 
   packet to be played out has not been received, the CEP de-packetizer 
   will play out an empty packet onto the SONET interface in place of 
   the unavailable packet." What is the definition of this empty packet ?

5) From 7.2.2   STS SPE Unequipped Indication  : "The CEP de-packetizer MUST
use this 
   information to transmit a packet of all zeros onto the SONET/SDH 
   interface, and adjust the payload pointer as necessary." To cause the CE
to 
   recognize the Unequipped condition, the only thing we have to do is to
set byte C2 of 
  Path Overhead to zero. No need in payload zeroing...

thanks,
  Akiva

---

From: "tom k. johnson" <[email-masked]>
Date: Mon, 1 Jul 2002 14:45:59 -0400

Akiva - 

>   consistent with one of these SHOULDs dropped. 

Agreed.  This was part of an unfortunate episode where I found out after that fact that some folks had implemented with an eye toward long-word alignment and others had implemented with an eye towards 783 byte alignment.  I'm thinking that we should keep the 783 byte MUST and all the SHOULDs should be long-word aligned.  But, I'm open to suggestion...

> As for me,  
> the statement of

I think the assumption is that it would be configured at PW setup.  But I suppose there's no reason it couldn't be adjusted during operation.  Although any change in jitter buffer depth during run-time would be accompanied by errors in the reassembled SPE.

>    (same as jitter buffer) length.

I suppose that's true.  I guess the point we were trying to make is that any packet received after it's play-out time would definitely be considered invalid.  

>    the unavailable packet." What is the definition of this 

It would be a packet where the payload area is filled with a fixed byte pattern (for example all ones).

>   Path Overhead to zero. No need in payload zeroing...

That is what the text says.  But, you're not the only one who has raised this as a question.  And, I belive there's some contradictory text elsewhere in the draft that indicates that Unequipped will be generated when packet stream is received that happens to have all zeros in the payload.  So, we probably need to scrub that aspect of the draft to make it coherent.

Hope that helps...

-Tom

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