Re: [HSSG] Jumbo frames
I agree with you about jumbo frames. I am glad
that Joel mentioned it though because it is a good discussion to get out of the
way. I had a couple of other thoughts about the issues with jumbo frames
and I'd appreciate your feedback (as the P802.3as chair) and that of others with
more MAC standards expertise (Shimon, Larry, etc.):
1) 802.3as is expanding the Ethernet frame, but this
was done in conjunction with 802.1. Therefore, I would assume that any
jumbo frame project would require the same effort.
2) The 802.3 MAC specification doesn't "buffer"
information; therefore, a change in the MAC would be required to perform this
operation to be compliant with the 802.3 MAC service
3) Would this have impact on other 802 dots (.11, .17,
etc.) if something was done in conjunction with 802.1?
I know that jumbo frames have been brought up in the
past. Most previous projects have rejected doing it, and in my humble
opinion, the primary reason has been that the change is more complex than just
altering the 802.3 MAC frame size.
Joel's statement below can
be grossly misinterpreted. He states that all system and silicon vendor supports
jumbo frames. That may be true but I highly doubt it. However, what is not
true is that all or the even the majority of the installed base of Ethernet gear
supports jumbo frames. In addition, many products on the market today do not
support jumbo frames (by products I mean both equipment and silicon). During the
P802.3as Frame Expansion project (soon to complete), UNH IOL kindly tested
hundreds of pieces of gear and combed through hundreds of reports to determine
the maximum frame size supported by Ethernet gear (that had been submitted to
UNH). While not exhaustive, the data indicated a wide range of maximums from
1515 (not a typo) through 2K, 4K, 5K, and 9K and beyond.
Within P802.3as, we
discussed jumbo frames at various times. The following constitutes my
recollection of the reasons against "standardizing jumbo frames" (not
1) Interoperability with
2) Increasing frame size is
a slippery slope. Why 9KB? Why not something larger, like 16KB or
3) The network performance
bottlenecks change over time. Each major component of the network/system goes
through improvements and upgrades, which changes the requirements on other parts
of the network/system.
4) QoS (frame delay, frame
delay variation, etc.) impacts
Note from archive attached
If I go
to any search engine and input "jumbo ethernet
frames chips", I will see that every system and silicon vendor supports
jumbo ethernet frames.
My question is not
wether to support jumbos, because we all already do ... my question is
should we finally spec it out? I think we should, at a minimum,