Updated optical.py to allow parametrized topologies.

 #!/usr/bin/env python
 
-''' file: custom/optical.py '''
+''' file: optical.py '''
 
 from mininet.topo import Topo
+from mininet.node import RemoteController
 from mininet.net import Mininet
 from mininet.cli import CLI
 from mininet.log import setLogLevel, info
+from mininet.link import Intf, Link
 from mininet.util import irange
 
+class NullIntf( Intf ):
+    "A dummy interface with a blank name that doesn't do any configuration"
+    def __init__( self, name, **params ):
+        self.name = ''
+
+class NullLink( Link ):
+    "A dummy link that doesn't touch either interface"
+    def makeIntfPair( cls, intf1, intf2, addr1=None, addr2=None ):
+        pass
+    def delete( self ):
+        pass
+
 class OpticalTopo( Topo ):
 
-    def build( self, n=3, tapStart=3 ):
+    def addIntf( self, switch, intfName ):
+        "Add intf intfName to switch"
+        self.addLink( switch, switch, cls=NullLink,
+                      intfName1=intfName, cls2=NullIntf, intfName2=intfName )
+
+    def build( self, n=2, tapStart=3 ):
 
         # Add hosts and switches
         hosts = []
         switches = []
         for i in irange( 1, n ):
             h = self.addHost( 'h%d' % i )
-            s = self.addSwitch( 's%d' % i )
+            s = self.addSwitch( 's%d' % i, dpid="0000ffffffff%04d" % i )
             self.addLink( h, s )
             hosts.append( h )
             switches.append( s )
@@ -25,23 +44,23 @@ class OpticalTopo( Topo ):
         # Add optical tap interfaces
         tapNum = tapStart
         for sw in switches:
-            self.addLink( sw, sw, intfName1='%s-eth0' % sw, intfName2='tap%d' % tapNum )
+            self.addIntf( sw, 'tap%d' % tapNum )
             tapNum += 1
 
 # if you use, sudo mn --custom custom/optical.py, then register the topo:
-#sudo mn --custom optical-topo.py --topo optical,5
+#sudo mn --custom optical.py --topo optical,5
 topos = { 'optical': OpticalTopo }
 
 def installStaticFlows( net ):
-    for swName in [ 's1', 's2', 's3', 's4', 's5', 's6' ]:
-      info( 'Adding flows to %s...' % swName )
-      sw = net[ swName ]
+    for sw in net.switches:
+      info( 'Adding flows to %s...' % sw.name )
       sw.dpctl( 'add-flow', 'in_port=1,actions=output=2' )
       sw.dpctl( 'add-flow', 'in_port=2,actions=output=1' )
       info( sw.dpctl( 'dump-flows' ) )
 
-def run():
-    net = Mininet( topo=OpticalTopo() )
+def run( n ):
+    topo = OpticalTopo( n )
+    net = Mininet( topo=topo, controller=RemoteController, autoSetMacs=True )
     net.start()
     #installStaticFlows( net )
     CLI( net )
@@ -49,5 +68,12 @@ def run():
 
 # if the script is run directly (sudo custom/optical.py):
 if __name__ == '__main__':
+    import sys
+    try:
+        n = int( sys.argv[1] )
+    except:
+        print ( 'Usage: ./optical.py n    # n is number of switches\n'
+                'Starting with default of 2 switches...\n' )
+        n = 2
     setLogLevel( 'info' )
-    run()
+    run( n )