pox controller's forwarding.hub affects network latency

Question

I used to pox controller's forwarding.hub function in order to measure the effect of network latency on throughput of a ring topology with 10M bandwidth.

However, per my experiments, the effect of network latency changes seems have little impact on throughput(I used 0ms, 2ms,4ms,6ms,10ms). Theoretically, it should significantly impact the network throughput. So i wonder if Pox controller uses a different forwarding rules?

here are the code i used to generate the topology.

    fSwitch = None #the first switch
    lSwitch = None #the last switch

    for i in range(n):
        switch = self.addSwitch('s%s' % (i+1))
        host = self.addHost('h%s' % (i+1))
        self.addLink(host, switch,**lconfig)

        if lSwitch:
            self.addLink(switch, lSwitch,**lconfig)

        if i == 0:
            fSwitch = switch

        lSwitch = switch

    if n > 0:
        self.addLink(lSwitch, fSwitch,**lconfig)