[tforum] Re: [it-managers] Raising the Internet MTU

Tom Ammon tom.ammon@utah.edu
Thu, 19 Apr 2007 12:53:53 -0600


I think this kind of a simulation could be a relevant research project.

We have a few spare cisco boxes at CHPC. I would have to double check to 
make sure they aren't allocated for something else. If we could get 
someone to collaborate with us over a long-distance link, we could set 
up applications on both ends and mix jumbo and small frames. Is UEN 
interested in working on something like this? I think there is the 
potential here for us to make a real contribution to the frame size 
debate. It is pretty clear that the 802.3 working group is committed to 
keeping ethernet frame sizes as they are. There ought to be at least 
some investigation on the other side of the debate.

Tom


Julio Cesar Facelli wrote:
> It looks to me that this is a interesting problem to address in a lab,
> where you can control the traffics and simulate numerous patters and
> traffic mixes.
>
> Julio
>
> -----Original Message-----
> From: Josh Loveless [mailto:josh@uen.org] 
> Sent: Thursday, April 19, 2007 9:05 AM
> To: Thomas L Ammon
> Cc: Joe Breen; network-research@lists.utah.edu; tforum@uen.org;
> it-managers@lists.utah.edu
> Subject: RE: [it-managers] Raising the Internet MTU
>
> All,
>
> I think that the passion comes from the research community...  
>
> On the other hand, we have proved that jumbo frames certainly have their
> place. Jumbo frames belong in environments where bandwidth and
> serialization
> delays are low enough that intermixing jumbo frames and standard frames
> are
> of little concern.  Also if you are doing BGP updates for large tables
> in a
> real time environment jumbo frames are a must.
>
> The real question is - what happens when all applications and hosts (ie
> iTunes, eMule and other bandwidth hogs) are using jumbo frames?  Does
> our
> delay and jitter on a Gigabit or TenGigabit network go back to the days
> of
> fT1 and suboptimal frame relay speeds?  Studies like this one make good
> points... 
>
>  http://sd.wareonearth.com/~phil/jumbo.html
>
> ... but I think the argument will continue until we see a working real
> life
> implementation of jumbo frames from application to application on a
> large
> network.
>
>
> Joshua Loveless CCIET #16638
> Utah Education Network - Network Engineering
> Phone: (801) 585-1133
> Cell: (801) 647-4436
> Email: josh@uen.org
>  
>
> -----Original Message-----
> From: Tom Ammon [mailto:tom.ammon@utah.edu] 
> Sent: Wednesday, April 18, 2007 4:38 PM
> To: Josh Loveless
> Cc: Joe Breen; network-research@lists.utah.edu; tforum@uen.org;
> it-managers@lists.utah.edu
> Subject: Re: [it-managers] Raising the Internet MTU
>
> Just as a general (nontechnical) question-
>
> It seems that the discussion over jumbo frames is almost a religious 
> one- people seem to be very passionate about it, one way or the other. 
> What caused this kind of polarity? Did somebody in the IETF got his 
> lunch eaten over it or something?
>
> Tom
>
> Josh Loveless wrote:
>   
>> I do not have any hard data on actual jitter caused by jumbo frames.
>> However, you might be interested to know the UEN applies a 9000 byte
>>     
> MTU
> to
>   
>> any Gigabit Link in our PoPs.  In most cases our maximum jitter is .1
>>     
> ms.
>   
>> We have been running this way for about three years now. 
>>
>> We have found in most cases the actual packet size is limited by the
>> applications sending and receiving the data.  Also keep in mind that
>>     
> the
> MTU
>   
>> at the edge where the applications connect is usually a standard MTU.
>>     
> We
>   
>> use the jumbo frames primarily for routing protocol updates.  Using a
>>     
> larger
>   
>> frame allows BGP to converge significantly faster.
>>
>> We also require all new ethernet connections (with a few exceptions
>>     
> for
>   
>> rural areas) to support jumbo frames, just as an FYI.
>>
>> Thanks, 
>>
>> Joshua Loveless CCIET #16638
>> Utah Education Network - Network Engineering
>> Phone: (801) 585-1133
>> Cell: (801) 647-4436
>> Email: josh@uen.org
>>  
>>
>> -----Original Message-----
>> From: Joe Breen [mailto:Joe.Breen@utah.edu] 
>> Sent: Wednesday, April 18, 2007 11:47 AM
>> To: Tom Ammon
>> Cc: network-research@lists.utah.edu; tforum@uen.org;
>> it-managers@lists.utah.edu
>> Subject: Re: [it-managers] Raising the Internet MTU
>>
>>
>>
>>
>> Tom Ammon wrote:
>>   
>>     
>>> Has anyone seen any data concerning large frame size's impact on
>>>       
> jitter?
>   
>>>     
>>>       
>> Tom,
>>
>> As the speed of the link goes up, the impact of larger frame sizes
>>     
> goes 
>   
>> down unless the frame sizes grow significantly.  What you bring up is
>>     
> a 
>   
>> valid question, though, because you don't want latency sensitive 
>> volkswagen beetles stuck behind huge semi-trucks, or latency sensitive
>>     
>
>   
>> voice packets trapped in the queues behind large file transfers.  Some
>>     
>
>   
>> discussion exists in some of the links off of the main link I sent
>>     
> out. 
>   
>>   For example, Phil Dykstra's discussion:
>> http://sd.wareonearth.com/~phil/jumbo.html
>>
>> I will have to dig up some other links I have seen on the subject. 
>> There have been some rigorous papers dealing with the question.
>>
>> In practice, most jitter on voice and multimedia comes from dropped 
>> packets, varying latencies due to changing paths, routers running
>>     
> under 
>   
>> high utilization, strange asymmetric routes or host issues.  As long
>>     
> as 
>   
>> the pipes are fast, packet drop negligible and the routers are truly 
>> running wire speed, jitter issues tend to be lower.   Buffer sizes on 
>> hosts, routers and switches can affect jitter.  Host CPU utilization 
>> also affects jitter.  How well a host is handling interrupts also 
>> affects jitter.  Many factors affect jitter, especially in the Wide
>>     
> Area 
>   
>> Network.
>>
>> Large frame sizes are typically not common on the internet due to ISPs
>>     
>
>   
>> and end-customer devices not supporting Jumbo frames.   However, in
>>     
> the 
>   
>> research world, the national and international backbones do support 
>> jumbo frames as well as very high speed pipes.  Because the pipes are 
>> now 2.5Gigabit to 10Gigabit and the max Jumbo frame is only 9kbytes.
>>     
> A 
>   
>> 9kbyte frame on a 10Gig link is actually less of an impact than the 
>> standard 1500byte frame on a 10Megabit link.
>>
>> 	--Joe
>>
>>   
>>     
>>> Joe Breen wrote:
>>>     
>>>       
>>>> For those following network performance issues,
>>>>
>>>> As networks have progressed in speed from 10Megabit to 10Gigabit,
>>>>         
> the 
>   
>>>> size of the transmission unit has stayed the same.  This fact
>>>>         
> impacts 
>   
>>>> the performance of networks.  The following link is a very useful 
>>>> starting point on Jumbo-frames and larger Maximum Transmission
>>>>         
> Units.
>   
>>>> http://www.psc.edu/~mathis/MTU/
>>>>
>>>> Matt Mathis of the Pittsburgh SuperComputing Center is one of the 
>>>> leading investigators into larger packet sizes and their impact on 
>>>> performance.  He is also one of the co-authors of a new Request for 
>>>> Comment (RFC) regarding path MTU discovery, the ability for end 
>>>> machines to discover the maximum transmission unit.
>>>>
>>>>     --Joe
>>>>       
>>>>         
>>>     
>>>       
>>   
>>     
>
>
>