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RE: [RPRWG] control TTL




Hi,

The accompanying presentation hp_size
http://grouper.ieee.org/groups/802/17/documents/presentations/jul2001/hp_siz
e_02.pdf

concludes the upper bound on nodes should be 128, and that an 8-bit
TTL is sufficient.  This is why the motion Motion: 2001-05-17-08 was worded
that way.

	thanks,

	robert

-----Original Message-----
From: Anoop Ghanwani [mailto:anoop@xxxxxxxxxxxxxx]
Sent: Wednesday, June 19, 2002 10:13 AM
To: 'Harry Peng '; 'Tom Alexander '; 'stds-802-17@xxxxxxxx '
Cc: ''djz@xxxxxxxxxxx' '; 'John Lemon '; Anoop Ghanwani
Subject: RE: [RPRWG] control TTL



 
Harry,

Per my reading, the objective says that we will support
at least 64 nodes "with an objective to go up to 255 nodes".
I assume that we have 2 separate numbers in the objective
because it was thought that that might be issues going 
up to 255 nodes.  I wasn't active in this group back then,
so I'm not sure why it was worded in this way.

-Anoop

-----Original Message-----
From: Harry Peng
To: Tom Alexander; stds-802-17@xxxxxxxx
Cc: 'djz@xxxxxxxxxxx'; John Lemon; 'Anoop Ghanwani'
Sent: 6/19/02 6:54 AM
Subject: RE: [RPRWG] control TTL


Point of order 

One of our objective voted in is to support 255 stations on a ring. 
The motion was passed July 2001. 

Regards, 

Harry 


-----Original Message----- 
From: Tom Alexander [ mailto:Tom_Alexander@xxxxxxxxxxxxxx
<mailto:Tom_Alexander@xxxxxxxxxxxxxx> ] 
Sent: Tuesday, June 18, 2002 10:35 PM 
To: stds-802-17@xxxxxxxx 
Cc: 'djz@xxxxxxxxxxx'; John Lemon; 'Anoop Ghanwani' 
Subject: RE: [RPRWG] control TTL 



John, David, 

Both of these numbers arose out of the resolution to 
comment #155 on D0.2. Specifically, the comment wanted 
distance, speed and number of stations on the ring to 
be part of the statement of RPR performance objectives. 
The group resolution was as follows: 

  "Contributions are requested on the following topics: 
  what performance objectives (distance, speed, MAC 
  end-to-end delay, delay jitter, etc. for specific 
  configurations) should be specified? What should these 
  objectives be for the RPR MAC? 

  Recommendations: The maximum number of stations should 
  be defined compatible with an 8-bit TTL field, as 
  determined by Clauses 6 and 11. The maximum ring size 
  should be set to 2000 km. As for the remainder, 
  contributions are requested." 

With regard to the distance, there is unfortunately no 
clause in D0.2 where a distance is specified at all, let 
alone in a normative manner. Therefore, the CRG followed 
what it believed to be the stated intent of the WG, and 
set the distance placeholder in D0.2 to 2000 km. There 
was no intent that this should be normative; in fact, an 
editor's note at the very beginning of Clause 1 explicitly 
states that none of the material in the clause is 
normative. 

With regard to the number of stations on the ring, the 
resolution simply requests that the number of stations 
should be defined 'consistent with an 8-bit TTL'. It was 
stated at the time that an 8-bit TTL limits one to 127 
stations (< 255 nodes, each station counting as two nodes) 
to cover the case of a wrapped ring. Therefore, the only 
means available to the editor of satisfying that resolution 
was to put down "127" as the number of stations in the 
objectives. 

It is entirely possible that one or both of the above 
numbers is incorrect or unsatisfactory; this is why the 
comment resolution group started off by requesting 
contributions on the objectives. Clearly, the conversion 
of the placeholders to actual numbers has had the beneficial 
effect of sparking the discussions necessary to produce 
such contributions! 

Best regards, 

- Tom A. 
Chief Editor, P802.17 


-----Original Message----- 
From: David James [ mailto:djz@xxxxxxxxxxx <mailto:djz@xxxxxxxxxxx> ] 
Sent: Tuesday, June 18, 2002 6:43 PM 
To: John Lemon; 'Anoop Ghanwani'; stds-802-17@xxxxxxxx 
Cc: Tom Alexander 
Subject: RE: [RPRWG] control TTL 


John, 

From my recollection, there were items that affected the whole 
draft, rather than specific clauses, and this was one of them. 
That ad-hoc resolution group addressed this and other issues, 
or so I thought. Have to ask Tom Alexander on the details. 

Regardless of recollection, this number is consistent with 
a past working group decision. There are painful repercussions 
in having numbers set at 255, since the number of attachment 
points (that can all be legally visited once) is twice the 
number of stations and should be counted in the TTL field. 

And, I'm most interest in what possible technical reason 
could be used to justify such a large number of devices? 
Particulary when each chip may be required to support 
things like discovery tables. No point is having all 
chips support a large theoretical maximum, when it 
rarely (if ever) will be utilized. 

DVJ 


David V. James, PhD 
Chief Architect 
Network Processing Solutions 
Data Communications Division 
Cypress Semiconductor, Bldg #3 
3901 North First Street 
San Jose, CA 95134-1599 
Work: +1.408.545.7560 
Cell: +1.650.954.6906 
Fax:  +1.408.456.1962 
Work: djz@xxxxxxxxxxx 
Base: dvj@xxxxxxxxxxxx 

> -----Original Message----- 
> From: owner-stds-802-17@xxxxxxxxxxxxxxxxxx 
> [ mailto:owner-stds-802-17@xxxxxxxxxxxxxxxxxx
<mailto:owner-stds-802-17@xxxxxxxxxxxxxxxxxx> ]On Behalf Of John Lemon 
> Sent: Tuesday, June 18, 2002 5:44 PM 
> To: 'Anoop Ghanwani'; 'stds-802-17@xxxxxxxx' 
> Cc: Tom Alexander (E-mail) 
> Subject: RE: [RPRWG] control TTL 
> 
> 
> 
> The maximum number of stations on a ring is 255, not 127. I have no
idea why 
> someone changed clause 1; but clauses 8, 9, 10, 11, and E all use a
value of 
> 255. And the resolution of comments 155 and 431 support this. The
Overview 
> is informative, and is supposed to reflect a simple summary of what
has been 
> decided in the normative clauses. 
> 
> (As an aside, while I have no problem with 2000 km as a recommended
limit, 
> I'm also troubled that such technical changes are being made in the
Overview 
> instead of one of the normative clauses. The Overview should be
reflecting 
> what has been decided in the other clauses, not making its own
decisions.) 
> 
> jl 
> 
> -----Original Message----- 
> From: Anoop Ghanwani [ mailto:anoop@xxxxxxxxxxxxxx
<mailto:anoop@xxxxxxxxxxxxxx> ] 
> Sent: Tuesday, June 18, 2002 3:47 PM 
> To: 'stds-802-17@xxxxxxxx' 
> Subject: [RPRWG] control TTL 
> 
> 
> 
> 
> At the last meeting I had a comment requesting more 
> information on why the control TTL is 2 bytes.  The 
> explanation provided was that 1 byte is not sufficient 
> if we have 255 stations and are wrapping.  With D0.3, 
> the maximum number of stations is 127.  So now I 
> don't see a reason for a 2-byte control TTL.  I'm 
> about to submit another comment for this, unless I 
> can be convinced of a technical reason for a 2-byte 
> control TTL. 
> 
> -Anoop 
> -- 
> Anoop Ghanwani - Lantern Communications - 408-521-6707 
>