Outline q Background q Transmission Protocols q ALOHA

Outline q Background q Transmission Protocols q ALOHA q CSMA/CD q CSMA/CA q Network Devices q Hub q Switch q Access Point (AP) q Simulation Software - NCTUns q Background q Supported simulation function q User interface q Experiment q Goals & Experiment methods q Wired Networking q Wireless Networking q Simulation result 2

Background (1/2) q Why simulations are needed q. Plan a new networking topology q. Estimate the efficiency of networks q. Evaluate new protocols or devices q Advantages q. Lower cost q. Easy to build q. Avoid environmental interference 3

Background (2/2) q Goal of this experiment q. Learn to use the tool of NCTUNS q. Realize the mechanisms of q. Transmission protocols q. Network devices q. Methodlogy of designing an experiment 4

Transmission Protocols (1/2) q ALOHA q Transmit data only q Two types q Pure-Aloha q Slotted-Aloha q No sensing for collision and congestion q Channel throughput: 18% (Stallings, 2000) q CSMA (Carrier Sense Multiple Access) q Sense the media and transmit data if it’s idle q Two implementations: q Persistent CSMA q Non-persistent CSMA q Throughput is much better: over 40% 5

Transmission Protocols (2/2) q CSMA/CD q. CSMA with Collision Detection q. Wait a random time if collision and then transmit q. Used in wired networks (ex: IEEE 802. 3) q CSMA/CA q. CSMA with Collision Avoidance q. RTS/CTS mechanism for hidden terminals problems q. Used in wireless networks (ex: IEEE 802. 11) 6

Network Devices q Hub q Broadcast all packets to every port q Switch q Build a table for mapping between MAC addresses and ports q Broadcast packets at first time to verify the target port q Send packets to the target port instead of broadcasting q Access Point (AP) q A bridge for wired and wireless networks q Use RTS/CTS mechanism on wireless network q Always broadcast because of the media 7

Simulation Software - NCTUns q Background q. Developed by the Network and System Laboratory (NSL) of NCTU CS q. Used in both wired and wireless IP networks q. Directly uses the Linux ’s TCP/IP protocol stack q. Open-Source Simulation engine q. Provides complete and high-quality documentations q. Continuously supported, maintained and improved 8

Supported Simulation Functions q Flexibility of creating user’s own q Traffic generator q Configuration Tool q Monitor Tool q Different and new types of networks q Various networking devices and protocols q Generate repeatable simulation results q 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) q Four modes: q. Draw Topology q. Draw topology by using the network device toolbox q. Edit Property q. Enter each device and set their property and reporting information q. Run Simulation q. Start simulation and recording the report q. Play Back q. Use GUI interface to replay the simulation 11

Experiment q Goals : q Find the relationship between the offered load and throughput q Experiment methods q Use different offered loads to run simulations and compare the results q Offered load: q Capacity of the line divided by the amount of input data q Throughput : q The maximum of data rate the network can transmit 12

Experiment: Wired Networking q Use hubs and switches with different offered loads to run simulations q Example topologies: 13

Experiment: Wireless Networking q Use mobile hosts, access points (AP) with different offered loads to run simulations q Example topologies: 14

Results q Use [plot graph] tool to draw the throughput graph q Example graphs: The unit of values depend on the log file you selected 15