TCP maximum throughput... LFN's

So in my previous post on Nagle's Algorithm I mentioned educating folks on maximum theoretical TCP throughput over Long Fat Networks  (LFN's) during a cross country Data Center migration.

I thought it might be a good idea to post a few of the calculations you can do yourself if so inclined.  There are quite a few web sites that will do this for you but I believe its a basic calculation a Network Engineer should know how to do, if for no other reason than to be able to "check the work" of those websites.

Calculating Maximum theoretical throughput
 
   tcp window in bits / latency in seconds  =  throughput (bps)

So to calculate the following:
   1.)  64KB Window Size
   2.)  50ms Round trip time
   3.)  Say 45mbp/s link
   4.)  Assume 0% packet loss for now

Convert Max TCP window to bits
  64KB = 65535 bytes   65535 * 8 =  524280 bits
Divide bits by latency in milliseconds
  524280 / .050 =  10485600 which is 10.4 mbp/s per flow

This is just the basic calculation and does not take into account congestion and congestion avoidance mechanisms, optimizations that can (at a price) increase window size, etc.  I expect to share some more on this interesting subject over the next few posts.

If you have a great interest in this and desire further information sooner there are tags associated with this post you can google but I would also recommend this excellent and recently updated book.
TCP/IP Illustrated Volume I