Re: Jumbo frames

["Stephen Sprunk" <stephen () sprunk org>]

Thus spake "Andy Davidson" <andy () 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.

S

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