Re: [Bloat] Jumbo frames and LAN buffers

["Richard Scheffenegger" <rscheff@gmx.at>]

Also found this:
http://www.stanford.edu/~balaji/papers/QCN.pdf

Jim, you may notice that the congestion feedback probability function looks 
just like the basic RED marking function :)

Regards,
  Richard

----- Original Message ----- 
From: "Richard Scheffenegger" <rscheff@gmx.at>
To: "Kevin Gross" <kevin.gross@avanw.com>; <bloat@lists.bufferbloat.net>
Sent: Monday, May 16, 2011 8:36 PM
Subject: Re: [Bloat] Jumbo frames and LAN buffers


> Kevin,
>
>> My understanding is that 802.1au, "lossless Ethernet", was designed
>> primarily to allow Fibre Channel to be carried over 10 GbE so that SAN 
>> and
>> LAN can share a common infrastructure in datacenters. I don't believe 
>> anyone
>> intends for it to be enabled for traffic classes carrying TCP.
>
> Well, QCN requires a L2 MAC sender, network and receiver cooperation (thus 
> you need fancy "CNA" converged network adapters, to start using it - these 
> would be reaction/reflection points; plus the congestion points - 
> switches - would need HW support too; nothing one can buy today; 
> higher-grade (carrier?) switches may have the reaction/reflection points 
> built into them, and could use legacy 802.3x signalling outside the 
> 802.1Qau cloud).
>
> The following may be too simplistic
>
> Once the hardware has a reaction point support, it classifies traffic, and 
> calculates the per flow congestion of the path (with flow really being the 
> classification rules by the sender), the intermediates / receiver sample 
> the flow and return the congestion back to the sender - and within the 
> sender, a token bucket-like rate limiter will adjust the sending rate of 
> the appropriate flow(s) to adjust to the observed network conditions.
>
> http://www.stanford.edu/~balaji/presentations/au-prabhakar-qcn-description.pdf
> http://www.ieee802.org/1/files/public/docs2007/au-pan-qcn-details-053007.pdf
>
> The congestion control loop has a lot of similarities to TCP CC as you 
> will note...
>
> Also, I haven't found out how fine-grained the classification is supposed 
> to be (per L2 address pair? Group of flows? Which hashing then to use for 
> mapping L2 flows into those groups between reaction/congestion/reflection 
> points...).
>
>
> Anyway, for the here and now, this is pretty much esoteric stuff not 
> relevant in this context :)
>
> Best regards,
>  Richard
>
> ----- Original Message ----- 
> From: "Kevin Gross" <kevin.gross@avanw.com>
> To: <bloat@lists.bufferbloat.net>
> Sent: Monday, May 16, 2011 3:15 PM
> Subject: Re: [Bloat] Jumbo frames and LAN buffers
>
>
>> All the stand-alone switches I've looked at recently either do not 
>> support
>> 802.3x or support it in the (desireable) manner described in the last
>> paragraph of the linked blog post. I don't believe Ethernet flow control 
>> is
>> a factor in current LANs. I'd be interested to know the specifics if 
>> anyone
>> sees it differently.
>>
>> My understanding is that 802.1au, "lossless Ethernet", was designed
>> primarily to allow Fibre Channel to be carried over 10 GbE so that SAN 
>> and
>> LAN can share a common infrastructure in datacenters. I don't believe 
>> anyone
>> intends for it to be enabled for traffic classes carrying TCP.
>>
>> Kevin Gross
>>
>> -----Original Message-----
>> From: bloat-bounces@lists.bufferbloat.net
>> [mailto:bloat-bounces@lists.bufferbloat.net] On Behalf Of Jim Gettys
>> Sent: Monday, May 16, 2011 5:24 AM
>> To: bloat@lists.bufferbloat.net
>> Subject: Re: [Bloat] Jumbo frames and LAN buffers
>>
>> Not necessarily out of knowledge or desire (since it isn't usually
>> controllable in the small switches you buy for home).  It can cause
>> trouble even in small environments as your house.
>>
>> http://virtualthreads.blogspot.com/2006/02/beware-ethernet-flow-control.html
>>
>> I know I'm at least three consumer switches deep, and it's not by choice.
>>                     - Jim
>>
>>
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>