North American Network Operators Group

Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical

Re: MTU of the Internet?

  • From: Frank Kastenholz
  • Date: Thu Feb 05 10:42:27 1998

At 09:11 AM 2/5/98 -0500, Eric Osborne wrote:
>
>I think that "triple" is perhaps an oversimplification.  This assumes that
>without a 576-byte MTU, all packets would be 1500-byte MTUs.  1500/576 ~=~ 3.
>
>Remember, there's three kinds of average: mean, median, mode.  While the mean 
>packet size may be 200-250 bytes, the mode and median are probably different.  
>I don't have any statistics on this, but I'd be willing to guess that if you 
>plotted the packet sizes frequency you'd see something like a bimodal curve, 
>with a small peak at around 64 (ping) and a larger one near 1500 (10Mbit 
>Ethernet/T1 MTU).  As to median packet size, I have no idea.  It's probably 
>somewhere in the middle.  :)

the real data sez...
packet size distribution is roughly tri-modal
the 25-jun-97 numbers show
- roughly 38%  at 40bytes (tcp acks mostly)
-           .6    41
-          6%     44      (syn+mss)
-          1      52
-         10%     55
-           .6    56
-           .7    61
-          5%     576
-         12%     1500
nothing else accounts for >0.5% of the packets

and for those that really care
- 40 byte packets represent ~  4% of the bytes-on-the-fiber
- 552                         16
- 576                          8%
- 1500                        49%

the median packet size is 56 bytes

(http://www.nlanr.net/NA/Learn/packetsizes.html)