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Transcript
實驗五:媒介存取協定模擬 教師: 助教: 1 Outline Background Transmission Protocols ALOHA CSMA/CD CSMA/CA Network Devices Hub Switch Access Point (AP) Simulation Software - NCTUns Background Supported simulation function User interface Experiment Goals & Experiment methods Wired Networking Wireless Networking Simulation result 2 Background (1/2) Why simulations are needed Plan a new networking topology Estimate the efficiency of networks Evaluate new protocols or devices Advantages Lower cost Easy to build Avoid environmental interference 3 Background (2/2) Goal of this experiment Learn to use the tool of NCTUNS Realize the mechanisms of Transmission protocols Network devices Methodlogy of designing an experiment 4 Transmission Protocols (1/2) ALOHA Transmit data only Two types Pure-Aloha Slotted-Aloha No sensing for collision and congestion Channel throughput: 18% (Stallings, 2000) CSMA (Carrier Sense Multiple Access) Sense the media and transmit data if it’s idle Two implementations: Persistent CSMA Non-persistent CSMA Throughput is much better: over 40% 5 Transmission Protocols (2/2) CSMA/CD CSMA with Collision Detection Wait a random time if collision and then transmit Used in wired networks (ex: IEEE 802.3) CSMA/CA CSMA with Collision Avoidance RTS/CTS mechanism for hidden terminals problems Used in wireless networks (ex: IEEE 802.11) 6 Network Devices Hub Broadcast all packets to every port Switch Build a table for mapping between MAC addresses and ports Broadcast packets at first time to verify the target port Send packets to the target port instead of broadcasting Access Point (AP) A bridge for wired and wireless networks Use RTS/CTS mechanism on wireless network Always broadcast because of the media 7 Simulation Software - NCTUns Background Developed by the Network and System Laboratory (NSL) of NCTU CS Used in both wired and wireless IP networks Directly uses the Linux ’s TCP/IP protocol stack Open-Source Simulation engine Provides complete and high-quality documentations Continuously supported, maintained and improved 8 Supported Simulation Functions Flexibility of creating user’s own Traffic generator Configuration Tool Monitor Tool Different and new types of networks Various networking devices and protocols Generate repeatable simulation results Remote and concurrent simulations 9 User Interface (1/2) Assignment tools Network device Mode selector Zoom tools Topology plane Location info. Time bar Playback tools 10 User Interface (2/2) Four modes: Draw Topology Draw topology by using the network device toolbox Edit Property Enter each device and set their property and reporting information Run Simulation Start simulation and recording the report Play Back Use GUI interface to replay the simulation 11 Experiment Goals : Find the relationship between the offered load and throughput Experiment methods Use different offered loads to run simulations and compare the results Offered load: Capacity of the line divided by the amount of input data offered _ load input (kbps) capacity(kbps) Throughput : The maximum of data rate the network can transmit throughput output(kbps) capacity(kbps) 12 Experiment: Wired Networking Use hubs and switches with different offered loads to run simulations Example topologies: 13 Experiment: Wireless Networking Use mobile hosts, access points (AP) with different offered loads to run simulations Example topologies: 14 Results Use [plot graph] tool to draw the throughput graph Example graphs: The unit of values depend on the log file you selected 15