Jumbo frames

Stephen Sprunk stephen at sprunk.org
Fri Mar 30 16:33:59 UTC 2007

Thus spake "Andy Davidson" <andy at nosignal.org>
> The original poster was talking about a streaming application - 
> increasing the frame size can cause it take longer for frames to fill  a 
> packet and then hit the wire increasing actual latency in your 
> application.
> Probably doesn't matter when the stream is text, but as voice and  video 
> get pushed around via IP more and more, this will matter.

It's a serious issue for voice due to the (relatively) low bandwidth, which 
is why most voice products only put 10-30ms of data in each packet.

Video, OTOH, requires sufficient bandwidth that packetization time is almost 
irrelevant.  With a highly compressed 1Mbit/s stream you're looking at 12ms 
to fill a 1500B packet vs 82ms to fill a 10kB packet.  It's longer, yes, but 
you need jitter buffers of 100-200ms to do real-time media across the 
Internet, so that and speed-of-light issues are the dominant factors in 
application latency.  And, as bandwidth inevitably grows (e.g. ATSC 1080i or 
720p take up to 19Mbit/s), packetization time quickly fades into the 
background noise.

Now, if we were talking about greater-than-64kB jumbograms, that might be 
another story, but most folks today use "jumbo" to mean packets of 8kB to 
10kB, and "baby jumbos" to mean 2kB to 3kB.


Stephen Sprunk      "Those people who think they know everything
CCIE #3723         are a great annoyance to those of us who do."
K5SSS                                             --Isaac Asimov 

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