srtt.py

#!/usr/bin/env python
# Round Trip Time -> Smoothed RTT -> 
#  -> Retransmission Timeout (RTO) Simulation
# See RFC 793 http://www.faqs.org/rfcs/rfc793.html
import random
import pylab

alpha = 0.8
beta = 2.0
ubound = 20.0
lbound = 10.0

rtt = [random.randrange(2,10) for i in range(100)]
srtt = [0.0]
for i in range(1,100):
    srtt.append(alpha * srtt[i-1] + ((1 - alpha) * rtt[i]))
rto = [min(ubound, max(lbound, beta*srtt[i])) for i in range(100)]
pylab.plot(rtt)
pylab.plot(srtt)
pylab.plot(rto)
pylab.show()