Jumbo Frames?

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Apr 15th, 2006
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Hello's...


Could anyone give me a synopsis of the pro's and con's of Jumbo Frames? What does it do? Just bump up the MTU to 9000 instead of 1500? Do most devices support this now?


As for home networks, I use Linksys gear... Do any Linksys products support Jumbo Frames?


Thanks for any info

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balajitvk Sun, 04/16/2006 - 22:03
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Hi,


Large IP frames, also called "jumbograms" or "jumbo frames," have been recommended for high-performance networks. The MTU is set independently for every interface in an IP flow's path, and any interface can limit the size of the flow by fragmenting it.


Jumbo frames are Ethernet frames up to 9216 bytes (larger than the IEEE Ethernet maximum transmission unit [MTU]). This feature enables a device to forward frames as large as 9216 bytes, rather than declaring them "oversized" and discarding them.


Path MTU discovery, described in RFC1191, attempts to discover the optimal MTU for the path to avoid fragmentation


Jumbo frames are typically enabled to improve performance of large data transfers between servers.


Yes most of the newer devices support this option.


But i don't find any linksys support for that feature.


Hope this could give clarity on jumbo frames.


Rate if it does,

Rgs

adignan Mon, 06/05/2006 - 16:45
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Do you see any issues with enabling jumbo frames on a voice network?

scottmac Mon, 06/05/2006 - 19:35
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Oh yes .... big issues. You do not want to run jumbo frames on wireless, especiall in the b/g bands.


The main reason is interference ... one little glitch, and you've got to a) recognize that the (jumbo) frame was dropped, then b) get around to re-sending it. In a voice environment, that would be a completely trashed voice transmition.


If you do a trace of a Cisco VoIP system (wired), you'll note that the frames/packets are in the ~200 byte range (212, 222, something like that).


The reason is that it's more likely for a small frame to make it across the wire uncorrupted, it a much smaller chunk of voice to patch up if it is dropped / lost, and it gives the system (ala de-jitter) a better chance to adapt to a very dynamic environment.


Yes, there is a bit more overhead, but the payoff is higher voice quality (generally speaking ... fewer drops), and greater reliability.


Wireless, especially in the 802.11b/g bands is prone to a great deal of interference. Think of a jumbo frame as a jumbo target for interference, even in a relatively "quiet" environment, having more than one conversation with jumbos would be nearly impossible .... one client would have to wait while another was transmitting the huge frames (voice tend to use fixed / relatively same size packets).


Not a good thing. Data with jumbo frames on a wired environment is a Good Thing; Voice in jumbo frames over wireless would be a Very Bad Thing.


Hope this helps, Good Luck


Scott

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