Re: Jumbo Frames in 10GbE?

[gwinn@ed.ray.com (Joe Gwinn)]

At 1:05 PM 99/6/21, Larry Miller wrote:
>I have heard some folk lore that the CRC-32 algorithm rather suddenly falls
>apart (in terms of high detection rate) above the present maximum Ethernet
>block size (1518 bytes).

At 1:41 PM 99/6/21, Ted Schroeder wrote:
>Please check the document Error Characteristics of FDDI by Raj Jain.
>
>http://www.netlab.ohio-state.edu/~jain/papers/xie1.htm
>
>The CRC-32 algorithm breaks down at 11454 octets given the error
>characteristics he analyzes in his paper.

As the junbo-packet proposals are for 9,000-byte packets, this should not
be a problem.

In general, block checksums (such as the CRC) give a constant protection
per block, so the probability of accepting a damaged block rises linearly
with block size, assuming constant bit error rate.  Some coding schemes
produce bursts of errors for every raw error, complicating things.  This
seems to be the issue that Jain deals with, based on his abstract.


>Indeed, there have been some pleas for "no superpackets, please!" on this
>reflector.

Yes.  The technical rationales supporting these pleas would be interesting.

At 10 gigabit, what existing base is there to protect?  One would have
thought there was none.


>This should be carefully checked before making any great leaps, tempting
>though it may be from an overhead perspective.

Absolutely.

Joe Gwinn



>-----Original Message-----
>From: Joe Gwinn <gwinn@ed.ray.com>
>To: Booth, Brad <bbooth@level1.com>
>Cc: HSSG_reflector (E-mail) <stds-802-3-hssg@ieee.org>
>Date: Monday, June 21, 1999 12:34 PM
>Subject: Jumbo Frames in 10GbE?
>
>
>>
>>At 4:24 PM 99/6/17, Booth, Brad wrote:
>>>Just a small point.  One of the objectives that passed with greater than
>>>75% in Coeur d'Alene was to "preserve minimum and maximum FrameSize of
>>>current 802.3 Std."
>>
>>I don't know that the issue is going to stay decided all that long, based
>>on the recent article "Jumbo Frames gather support" (Jeff Caruso, Network
>>World, 14 June 1999, page 6), which states that IETF has published a
>>working document proposing that ethernet frames be made larger than the
>>current 1,500-byte maximum, the basic rationale being to reduce the packet
>>rate and thus load on packet-handling components of the system.  In short,
>>this is a system issue, and cannot really be decided solely at the MAC
>>level.
>>
>>If jumbo frames are to come, 10GbE would be a logical place to start.
>>
>>The issue will ultimately be decided by an IEEE Ballot Group, not a
>>Plenary.  If the market is really going to bigger packets, as this article
>>implies, it will be hard to resist.
>>
>>Joe Gwinn