A 2 hosts, 4 switch network that calculates OWD using a probe based algorithm.
Every test file is formatted as follows:
timestamp ingress switch 1 first time, timestamp egress switch 1 first time, timestamp ingress switch 2, timestamp egress switch 2, timestamp ingress switch 1 second time, timestamp egress switch 1 second time.
The RTT between 2 switches is calculated with the help of a probe. The probe goes through s1-s2 and s1 again. This choice is due to the fact that it is always better to use the same clock to measure a delay.
In figure, the RTT is equals to the sum of the red and purple paths. It is equals to: timestamp egress switch 1 second time - timestamp ingress switch 1 first time.
Then, the OWD is obtained by subtracting the red path from the RTT and by halving the result. We simply calculate a bunch of values to start with.
RS1(time spent in the first switch) = (timestamp egress switch 1 first time - timestamp ingress switch 1 first time) + (timestamp egress switch 1 second time - timestamp ingress switch 1 second time)
RS2(time spent in the second switch) = timestamp egress switch 2 - timestamp ingress switch 2
OWD = ( RTT - (RS1 + RS2) ) / 2
Every test is simulated through the use of linux traffic control (tc) with the help of a simulated Mininet network. The test results are divided in 2 cases: normal and good case. The error is the relative error and is calculated as follows:
RE =( (average value of delay measured - delay)/delay ) x 100
| delay(ms) | Normal case | Good case |
|---|---|---|
| 10 | 5.22% | 1.70% |
| 50 | 6.38% | 0.31% |
| 100 | 5.75% | 0.53% |
| 200 | 0.36% | 0.31% |
First, set the Mininet delay value. 1 - Go on the file test_topo.py and edit it. 2 - Go on line 45 and edit the value of delay in the line self.addLink(switch2, switch3, port1=3,port2=3, delay="200ms") - format are Xms, Xs, etc.. with X being the value of the delay
Then, open 2 terminals in P4_delayLink/.
In the first terminal run the following commands, to:
- generate a JSON file with the description of the basic.p4 rules
- start the topography described in test_topo.py
- open a terminal for every node - we will call them h1 and h4
p4c-bm2-ss --p4v 16 basic.p4 -o basic.json
sudo python start_test_topo.py
xterm h1 h4In the second terminal run the following commands, to install rules into the switches:
sudo python cmd_add.pyThen, in the h4 terminal, run the following command to start listening to TCP packets - you need to specify the file in which you want to save tests (-f option, csv file preferred)
./receive.py -f filename.csvThen, in the h1 terminal, run the following command to send 5 packets:
./sendT.shRun the following to calculate OWD, you will see RS1 and RS2 calculation, as well as RTT - you need to specify the file from which you want to calculate OWD (-f option, format specified above):
./calculate_OWD.py -f filename