lecture9 - Alan Mislove amislove at ccs.neu.edu...

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Unformatted text preview: Alan Mislove amislove at ccs.neu.edu Northeastern University 1 CS4700/CS5700 Fundamentals of Computer Networks Lecture 9: Bridging Slides used with permissions from Edward W. Knightly, T. S. Eugene Ng, Ion Stoica, Hui Zhang Alan Mislove amislove at ccs.neu.edu Northeastern University 2 Recap Broadcast network is a simple way to connect hosts Everyone hears everything Need MAC protocol to control medium sharing Problem: Cannot scale up to connect large number of nodes Too many nodes, too many collisions, goodput (throughput of useful data) goes to zero Broadcast technology host host host host host host host host Hub Hub emulates a broadcast channel Easy to add a new host Alan Mislove amislove at ccs.neu.edu Northeastern University 3 Need Switching Techniques Switching limits size of collision domains, allows network size to scale up To how big? Can Internet be one big switched Ethernet? Will return to this question Switches are more complex than hubs Intelligence, memory buffers, high performance host host host host host host host host host host host host Hub Switch Switch host host host host Alan Mislove amislove at ccs.neu.edu Northeastern University 4 Switch Switch has memory buffers to queue packets, reduce loss Switch is intelligent: Forward an incoming packet to the correct output interface only High performance: Full N x line rate possible input interface output interface Switch fabric input interface output interface Switch Hub N Alan Mislove amislove at ccs.neu.edu Northeastern University 5 Taxonomy of Networks Communication Network Circuit-Switched Network Packet-Switched Network Datagram Network Virtual Circuit Network Frequency Division Multiplexing Time Division Multiplexing Alan Mislove amislove at ccs.neu.edu Northeastern University 6 Building Large LAN Using Bridges Bridges connect multiple IEEE 802 LANs at layer 2 Datagram packet switching Only forward packets to the right port Reduce collision domain In contrast, hubs rebroadcast packets. host host host host host host host host host host host host Bridge Alan Mislove amislove at ccs.neu.edu Northeastern University 7 Transparent Bridges Overall design goal: Complete transparency Plug-and-play Self-configuring without hardware or software changes Bridges should not impact operation of existing LANs Three parts to transparent bridges: (1) Forwarding of Frames (2) Learning of Addresses (3) Spanning Tree Algorithm Alan Mislove amislove at ccs.neu.edu Northeastern University 8 Frame Forwarding Each bridge maintains a forwarding database with entries < MAC address, port, age> MAC address: host address or group address port: port number of bridge age: aging time of entry interpretation: a machine with MAC address lies in direction of the port number from the bridge. The entry is age time units old. Alan Mislove amislove at ccs.neu.edu Northeastern University 9 Assume a frame arrives on port x.Assume a frame arrives on port x....
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lecture9 - Alan Mislove amislove at ccs.neu.edu...

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