what about 48 bits?

Bill Bogstad bogstad at pobox.com
Mon Apr 5 15:54:06 UTC 2010


On Mon, Apr 5, 2010 at 12:05 AM, joel jaeggli <joelja at bogus.com> wrote:
> On 4/4/2010 7:57 PM, Richard A Steenbergen wrote:
>>
>> On Mon, Apr 05, 2010 at 10:57:46AM +0930, Mark Smith wrote:
>>>
>>> Has anybody considered lobbying the IEEE to do a point to point version
>>> of Ethernet to gets rid of addressing fields? Assuming an average 1024
>>> byte packet size, on a 10Gbps link they're wasting 100+ Mbps. 100GE /
>>> 1TE starts to make it even more worth doing.
>>
>> If you're lobbying to have the IEEE do something intelligent to Ethernet
>> why don't you start with a freaking standardization of jumbo frames. The
>> lack of a real standard and any type of negotiation protocol for two
>> devices under different administrative control are all but guaranteeing
>> end to end jumbo frame support will never be practical.
>
> Not that I disagree, given that we use them rather a lot but 7.2usec (at
> 10Gbe) is sort of a long time to wait before a store and forward arch switch
> gets down to the task of figuring out what to do with the packet. The
> problem gets worse if mtu sizes bigger than 9k ever become popular,  kind of
> like being stuck behind an elephant while boarding an elevator.

I didn't run the numbers,  but my guesstimate is that would be roughly
half the latency that a max sized standard packet would have taken on
a 1Gbe switch.   It sound reasonable to me that at some point during
the march from 10->100->1000->10000 mbit/sec a decision could have
been made that one of those upgrades would only decrease max. per hop
packet latency by a factor of 2 rather then 10.  Particularly since
when first introduced, each speed increment was typically used for
aggregating a bunch of slower speed links which meant that the actual
minimum total latency was already being  constrained by the latency on
those slower links anyway.

OTOH, I totally buy the argument on the difficulty of frame size
negotiation and backward compatibility.  I think that one of the
reasons for the continuing success of "Ethernet" technologies has been
implementation simplicity and 100% compatibility above the level of
the NIC.

Bill Bogstad




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