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Re: [RPRWG] Careful Use of the 802.3 PHY



Devendra, with all due respect, I believe the problem Bob Grow and Geoff Thompson appear to be having with 802.17 is specifically comments like "I do not see any issue with Ethernet."  What they believe our group should be doing (and Bob and Geoff, please correct me if I am incorrectly putting words in your mouths) is carefully reviewing the assumptions that went into developing the Ethernet (and SONET) PHY layers, and then thoroughly analyzing how they will behave in an 802.17 environment, given the differences in the way we are using those physical layers.  The real problem has been our willingness to handwave, rather than digging in and doing the difficult work.
 
I am hammering away at this point because I am concerned that it will come back to bite us during Sponsor ballot.  In addition, I believe we really have the time now to do the evaluations of our PHY layers carefully, within our schedule, and thereby go through sponsor ballot much more cleanly and quickly.
 
Best regards,
 
Robert D. Love
President, Resilient Packet Ring Alliance
President, LAN Connect Consultants
7105 Leveret Circle     Raleigh, NC 27615
Phone: 919 848-6773       Mobile: 919 810-7816
email: rdlove@xxxxxxxx          Fax: 208 978-1187
----- Original Message -----
Sent: Sunday, January 26, 2003 11:18 AM
Subject: RE: [RPRWG] Careful Use of the 802.3 PHY

I guess the only problem is with 802.3ac. With 18 additional byte the length becomes 1540 which is more than  0x600 (the limit for length by 802.3). I guess it will not be 802.3 frame any one. But I do not see any issue with Etheret.
 
Regards,
Devendra.
-----Original Message-----   
From: owner-stds-802-17@xxxxxxxxxxxxxxxxxx [mailto:owner-stds-802-17@xxxxxxxxxxxxxxxxxx]On Behalf Of Castellano, Robert
Sent: Friday, January 24, 2003 9:42 PM
To: Robert D. Love; 802.17
Cc: Thompson, Geoff O; Grow, Bob
Subject: RE: [RPRWG] Careful Use of the 802.3 PHY

Bob,
 
Are there any maximum frame size issues with either the 1Gbps or 10Gbps 802.3 PHY?  An RPR
frame adds 18 bytes on top of the standard 802.3 frame.
 
        thanks,
 
        robert
-----Original Message-----
From: Robert D. Love [mailto:rdlove@xxxxxxxxx]
Sent: Thursday, January 23, 2003 5:43 PM
To: 802.17
Cc: Thompson, Geoff O; Grow, Bob
Subject: [RPRWG] Careful Use of the 802.3 PHY

In order to look at possible stumbling blocks ahead of us at Sponsor Ballot time, I sent a note to Geoff Thompson and to Bob Grow with the following query:
 
Do either of you see any problem with 802.17 using a "standard 802.3 PHY" and supporting frame sizes less than 64 Bytes", especially if the data rates of interest are 1 and 10 Gbits/s?  Would you expect anyone in 802.3 to be upset with 802.17 requiring the PHY to support the small frame sizes?  (I realize that you can't know for sure how everyone will respond to this question.  I am just looking for your gut reaction here.  Thanks.) 
As I look ahead at the Sponsor level ballot, I want to steer around stumbling blocks and want to get an early peek at whether there is any reasonable standards conformance based reason to want to avoid requiring 802.17 PHYs from supporting these small frame sizes.  I expect that we will have a fair number of 802.3 voters in our sponsor ballot pool.
 
As it turns out, both Bob and Geoff have strong concerns with what we are doing. 
 
Geoff's has kindly given me permission to post his reply which was:
"A "standard" 802.3 PHY can not be used unaltered if it has Auto-Negotiation.
                (i.e. you can't just buy Ethernet chips and use them in 802.17 applications)
        We haven't even looked at the ramifications of having radically different path lengths between transmit and receive
        You lose a great deal of your resiliency if you use 1000BASE-T  links in an RPR ring.

Basically, I have grave reservations about using Ethernet chips in an application where you are throwing out a significant number of the basic design assumptions that were in hand when the PHYs were designed. These assumptions are not necessarily documented in any other fashion than that it was an Ethernet chip being designed. That, in and of itself, sets a large number of conditions. I don't think you get to use an Ethernet chip without examining each and every departure from Ethernet assumptions on an engineering basis at the detail level.

Do I know off the top of my head what ALL of the considerations are? No way! I haven't ever had the occasion to look at the appropriate level of depth that is required to develop product. I'm probably not even the right guy to do it as I am not a PHY designer at this point in my life. Can I think of a few off the top of my head? Yup, see above."
 
Bob Grow's reservations were even stronger.  There are two conclusions we should draw from Geoff's remarks.
(1) We should be studying very carefully, not only the requirements that we get from reading the specifications for the PHYs that we pick up, but the assumptions that went into the development of those PHYs
(2) We need to do comprehensive analysis to justify any change to the assumptions used in developing those PHYs.
 
The second conclusion implies that we need to do a great deal of work before assuming that the PHYs can be used for small frame size (less than 64 Bytes).  We may also want to ask the question as to whether the use of short frames is worth the risk of breaking Ethernet PHYs, especially is we are unable to do a comprehensive review of the Ethernet PHY requirements.  We should also look at the implications of large frame size, even though large frame sizes are used in proprietary products today. 
 
Note that problems uncovered during Sponsor Ballot can completely derail the standard and the schedule.  We don't want to be making any significant changes to the draft at sponsor ballot time.  Certainly changing the length of control frames would be highly significant.  We have work to do.  Let's decide how to best address it early enough to stay within our present schedule.
 
 
Best regards,
 
Robert D. Love
President, Resilient Packet Ring Alliance
President, LAN Connect Consultants
7105 Leveret Circle     Raleigh, NC 27615
Phone: 919 848-6773       Mobile: 919 810-7816
email: rdlove@xxxxxxxx          Fax: 208 978-1187