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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
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Background (1/2)
Why simulations are neededPlan a new networking topologyEstimate the efficiency of networksEvaluate new protocols or devices
AdvantagesLower costEasy to buildAvoid environmental interference
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Background (2/2)
Goal of this experimentLearn to use the tool of NCTUNSRealize the mechanisms of
Transmission protocolsNetwork devices
Methodlogy of designing an experiment
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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%
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Transmission Protocols (2/2)
CSMA/CDCSMA with Collision DetectionWait a random time if collision and then transmitUsed in wired networks (ex: IEEE 802.3)
CSMA/CACSMA with Collision AvoidanceRTS/CTS mechanism for hidden terminals problemsUsed in wireless networks (ex: IEEE 802.11)
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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
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Simulation Software - NCTUns
BackgroundDeveloped by the Network and System Laboratory (NSL)
of NCTU CSUsed in both wired and wireless IP networks Directly uses the Linux ’s TCP/IP protocol stack Open-Source Simulation engineProvides complete and high-quality documentationsContinuously supported, maintained and improved
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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
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User Interface (1/2)
Network device
Assignment tools
Zoom tools
Mode selector
Time bar Playback tools
Location info.
Topology plane
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User Interface (2/2)
Four modes:Draw Topology
Draw topology by using the network device toolboxEdit Property
Enter each device and set their property and reporting informationRun Simulation
Start simulation and recording the reportPlay Back
Use GUI interface to replay the simulation
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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
Throughput : The maximum of data rate the network can transmit
)(
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kbpscapacity
kbpsoutputthroughput
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kbpscapacity
kbpsinputloadoffered
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Experiment: Wired Networking
Use hubs and switches with different offered loads to run simulations Example topologies:
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Experiment: Wireless Networking
Use mobile hosts, access points (AP) with different offered loads to run simulations
Example topologies: