---
tags: mininet-wifi-tutorials
---

# Act 3 - OpenFlow Protocol

You now will learn and put into practice basic concepts of the OpenFlow protocol, such as idle/hard timeouts, and apply them into a wireless scenario to understand the impact in mobile communications.

## Activity 1: Mobility

Plese consider the content of handover.py below:

#!/usr/bin/python

'Example for handover'

from mn_wifi.net import Mininet_wifi
from mn_wifi.cli import CLI
from mininet.node import Controller
from mininet.log import setLogLevel


def topology():

    "Create a network."
    net = Mininet_wifi()

    print "*** Creating nodes"
    sta1 = net.addStation('sta1', mac='00:00:00:00:00:01', ip='10.0.0.1/8')
    ap1 = net.addAccessPoint('ap1', ssid='new-ssid1', mode='g',
                             channel='1', position='15,30,0')
    ap2 = net.addAccessPoint('ap2', ssid='new-ssid1', mode='g',
                             channel='6', position='55,30,0')
    s3 = net.addSwitch('s3')
    h1 = net.addHost('h1', mac='00:00:00:00:00:02', ip='10.0.0.2/8')
    c1 = net.addController('c1', controller=Controller, port=6653)

    net.setPropagationModel(model="logDistance", exp=5)

    print "*** Configuring WiFi Nodes"
    net.configureWifiNodes()

    #s3.plot(position='35,90,0')
    #h1.plot(position='35,80,0')

    print "*** Creating links"
    net.addLink(ap1, s3)
    net.addLink(ap2, s3)
    net.addLink(h1, s3)

    'plotting graph'
    net.plotGraph(max_x=100, max_y=100)

    net.startMobility(time=0, repetitions=1)
    net.mobility(sta1, 'start', time=1, position='10,30,0')
    net.mobility(sta1, 'stop', time=80, position='60,30,0')
    net.stopMobility(time=80)

    print "*** Starting network"
    net.build()
    c1.start()
    ap1.start([c1])
    ap2.start([c1])
    s3.start([c1])

    print "*** Running CLI"
    CLI(net)

    print "*** Stopping network"
    net.stop()

if __name__ == '__main__':
    setLogLevel('info')
    topology()    

and then run it:

~/mininet-wifi$ sudo python handover.py

Now, let h1 keep pinging sta1:

mininet-wifi>h1 ping sta1

**Question 1.1**: As you can see, h1 cannot reach sta1 when sta1 goes to ap2. Why? Two important commands should help you to answer this question:

mininet-wifi>links
mininet-wifi>sh ovs-ofctl dump-flows s3

_Tip: Observe both idle_timeout and idle_age._

**Question 1.2**: Now you know the answer, how could sta1 be reached by h1? Suggest (and prototype) some possible solutions.

## Activity 2: Remote Controller

In the activities made so far, the controller has run on your computer and in a somewhat abstract way. That is, we started Mininet-WiFi and the controller was started along with Mininet-WiFi. However, in the real world, the controller is installed and run on a known computer or server. Be it a physical computer or even a virtual machine. So, let’s run a test with a controller other than the ovs-testcontroller, the controller that starts with Mininet-WiFi. To do so, we will use the Ryu controller. The source code of Ryu can be found at https://github.com/osrg/ryu, however, we will consider for this activity a copy of the official repository available at https://github.com/ramonfontes/ryu, especially the branch book.

git clone https://github.com/ramonfontes/ryu -b book

To follow up on this tutorial, let’s then run the following command. The command sudo mn has been presented previously, however, we will use it next to the --controller parameter.

sudo mn --controller=remote

Now, let’s try a ping between h1 and h2.

mininet-wifi> h1 ping -c1 h2

**Question 2.1**: What happened? You now must start Ryu so that the nodes can communicate with each other. To do so, try to start Ryu on a new terminal. As the Ryu source code has been previously obtained, it can be started as follows.

~/mininet-wifi/ryu$ sudo PYTHONPATH=. ./bin/ryu-manager ryu/app/simple_switch_13.py

Now, let’s repeat the ping between h1 and h2.

mininet-wifi> h1 ping -c1 h2