1. Network Simulation One tool to simulation network protocols for the Internet is the network simulator (NS) The simulation environment needs to be set- up carefully to produce meaningful results The simulation set-up is called ‘simulation scenario’

2. Simulation Scenarios In general, a simulation scenario consists of three different main components (or dimensions) –Routed Topology –Connections, Traffic and Agents/end-host protocols –External events and Failures

3. Routed Topology Defines the number of nodes and their connectivity Defines the links connecting the nodes, their bandwidth, delay, queuing discipline and other characteristics Defines the routing protocols running in the nodes in terms of unicast and multicast routing Can use topology generators (e.g., GT-ITM)

4. Connections, Traffic and Agents Agents are end-host protocols, such as TCP, ftp, Telnet, UDP.. etc. Traffic source can be: (uses a traffic model) –constant bit rate (CBR) at rate R –with distribution (Poisson or Pareto) –trace driven Connection definition includes spatial distribution of connections (TCP sender/receiver, or group members)

5. External events and Failures External events include the temporal distribution of connections: –start and end of TCP connections –join/leave patterns for multicast group members Failures include link failures, packet loss patterns and congestion patterns and may follow a failure model or distribution Events may also include movement patterns of mobile hosts

6. The network simulator (NS) It is a packet-level discrete-event simulator The simulation engine is written in C++ and mainly handles the event-queue and per packet processing (such as TCP and forwarding caches) Most protocols (such as unicast/multicsat) routing protocols are implemented in Otcl (Object Tcl) Check the vint project catarina.usc.edu/vint, and follow the on-line step-by-step tutorial

7. Getting Started Download the ns from: –http://www.isi.edu/nsnam/ns –Tcl/tk, otcl, tclcl, ns Install ns in your system –Binary release is provided for windows 9x/NT –NS-allinone package is strongly recommended Download nam if visualization is needed –http://www.isi.edu/nsnam/nam –Included in ns-allinone package Get help from ns-users@isi.edu –check the mailing lists on the ns web page

8. What is ns otcl: Object-oriented support tclcl: C++ and otcl linkage Discrete event scheduler Data network (the Internet) components tcl8.0 otcl tclcl ns-2 Event Scheduler Network Component

9. Internals Discrete Event Scheduler Network Topology Routing Transport Application Packet Flow

10. Discrete Event Scheduler time_, uid_, next_, handler_ head_ -> handler_ -> handle() time_, uid_, next_, handler_ insert head_ ->

11. Network Topology - Node n0n1 Addr Classifier Port Classifier classifier_ dmux_ entry_ Node entry Unicast Node Multicast Classifier classifier_ dmux_ entry_ Node entry Multicast Node multiclassifier_

12. Network Topology - Link n0n1 enqT_queue_deqT_ drophead_drpT_ link_ttl_ n1 entry_ head_

13. Routing n0n1 Addr Classifier Port Classifier classifier_ dmux_ entry_ Node entry 0 1 enqT_queue_deqT_ drophead_drpT_ link_ttl_ n1 entry_ head_

14. Routing (cont.) n0n1 Addr Classifier Port Classifier classifier_ dmux_ entry_ 0 1 Addr Classifier Port Classifier classifier_ dmux_ entry_ 1 0 Link n0-n1 Link n1-n0

15. 0 1 Transport n0n1 Addr Classifier Port Classifier classifier_ dmux_ entry_ 0 Agent/TCP agents_ Addr Classifier Port Classifier classifier_ dmux_ entry_ 1 0 Link n0-n1 Link n1-n0 0 Agent/TCPSink agents_ dst_=1.0 dst_=0.0

16. Application 0 1 n0n1 Addr Classifier Port Classifier classifier_ dmux_ entry_ 0 Agent/TCP agents_ Addr Classifier Port Classifier classifier_ dmux_ entry_ 1 0 Link n0-n1 Link n1-n0 0 Agent/TCPSink agents_ dst_=1.0 dst_=0.0 Application/FTP

17. Packet Flow 0 1 n0n1 Addr Classifier Port Classifier entry_ 0 Agent/TCP Addr Classifier Port Classifier entry_ 1 0 Link n0-n1 Link n1-n0 0 Agent/TCPSink dst_=1.0 dst_=0.0 Application/FTP

18. NS\VINT web pages\tutorial: –http://catarina.usc.edu/vint –http://www.isi.edu/nsnam/vint –http://www.isi.edu/nsnam/ns/tutorial/index.html