topology

    import sys
    from nest.experiment import *
    from nest.topology import *
    from topo_helper import topo_helper
    from nest.topology.address_helper import AddressHelper

    class PodError(Exception):
        def __init__(self,message):
            self.message=message


    class Pod:
        def __init__(self,k,net,bw,delay):

            self.agg_switches=[Switch('as'+str(i+1)) for i in range(k/2)]
            self.edge_switches=[Switch('as'+str(i+1)) for i in range(k/2)]
            t=k**3/4

            self.hosts=[Node('h'+str(i+1)) for i in range(t)]
            '''
            Connections between host to Edge switch
            '''
            for i,switch in enumerate(self.edge_switches):
                start=i*(k/2)
                for j in range(start,start+k/2):
                    with net:
                        (i1,i2)=connect(switch,self.hosts[j])
                        i1.set_attributes(bw, delay)


            '''
            Connectins between edge switch to agg switch
            '''
            for a_switch in self.agg_switches:
                for e_switch in self.edge_switches:
                    with net:
                        (i1,i2)=connect(a_switch,e_switch)
                        i1.set_attributes(bw, delay)




    class Fat_tree_helper(topo_helper):
        def __init__(self,k,nid,bw='100mbit',delay='1ms'):

            super().__init__(bw,delay)

            if k<0:
                raise PodError("Negative pod count")
            elif k%2==1:
                raise PodError("Odd pod count")

            self.pod_cnt=k
            self.core_cnt=(k//2)**2
            self.core_switches=[Switch('cs'+str(i+1)) for i in range(self.core_cnt)]

            self.nid=Network(nid)
            self.blocks=[Pod(k,nid)]*k



            bw=topo_helper.get_bandwidth()
            delay=topo_helper.get_delay()

            '''
            Connections betwween core switch to agg switch
            '''

            for block in self.blocks:
                start=0
                for s in block.agg_switches:
                    for i in range(start,start+k/2):
                        t=self.core_switches[i]
                        with self.nid:
                            (i1,i2)=connect(s,t)
                            i1.set_attributes(bw, delay)


                    start+=(k/2)

            AddressHelper.assign_address()



        def __str__(self):
            return "This is Fat tree class"