i am using custom topology as shown in below how we add a flows in pox controller
net.addLink(Host1, Switch1, **linkopts )
net.addLink(Switch1, Switch2, **linkopts )
net.addLink(Switch1, Switch3, **linkopts )
net.addLink(Switch3, Switch4, **linkopts )
net.addLink(Switch2, Switch5, **linkopts )
net.addLink(Switch4, Switch5, **linkopts )
net.addLink(Switch4, Host2, **linkopts )