1. 1 The ns-2 Network Simulator H Plan: –Discuss discrete-event network simulation –Discuss ns-2 simulator in particular –Demonstration and examples: u Download, installation, and configuration u Network topology and traffic modeling u TCP protocol models, and wireless models u Simulation results u Automating simulation scripts

2. 2 Performance Evaluation Analytical Methods Simulation Methods Experimental Methods Time-DrivenEvent-DrivenMonte Carlo Sequential ParallelDistributed... ns-2...

3. 3 Discrete-Event Simulation (recap) H A system is modeled as a set of entities that affect each other via events H Each entity can have a set of states H Events happen at specific points in time and trigger state changes in the system H Very general technique, well-suited to modeling discrete systems and networks H Simulator has an event list, and processes events in timestamp order

4. 4 Network Simulation H In networking research, the simulation is often of the Internet (or part thereof!) H Entities: hosts, routers, links, buffers,… H Messages: packets sent by protocols H Events: state changes of the network as packets move through the system H A network simulation models the movement of data and/or control packets through the network, according to the protocols being modeled

5. 5 ns-2 H ns-2: one example of network simulator H Originally developed at USC/ISI H Public-domain (free!), with open-source code contributed by many people H Versions of ns: –ns: original version of ns –ns-2: current version, widely used –ns-3: currently under development/testing –pdns: parallel/distributed ns execution

6. 6 Basic Information about ns-2 H Widely used in networking research H Written mostly in C++ H Over 50,000 lines of code H Can download, compile, and install on most any Linux system (or Windows?) H Also has tcl/tk interface for defining and manipulating models H Optional network animation tool (nam) for tracing, playback, and visualization

7. 7 Using ns-2 H Download from ns-2 site H Extract and compile H Look at examples provided H Look at documentation available H Look at ns-2 book (U of Manitoba) H Configure some simple experiments H Try some simulation scripts

8. 8 Strengths of ns-2 H Everything you need to get started! H Models for hosts, links, routers, buffers H Detailed protocol models for TCP H Usable for configuring topology H Usable for configuring network traffic H Some modeling for wireless, mobility H Tracing and visualization support H Large community of users and resources available (doc, examples, etc)

9. 9 Weaknesses of ns-2 H Too much stuff to get started! (code,doc) H Minimal protocol models for IP H Weak models for wireless, mobility H Few models for application-layer traffic H Minimal validation of any ns-2 models H Extracting results and statistics is hard H Debugging large and complex models H Cryptic error messages and crashes H Compatibility across ns-2 versions

10. 10 Some ns-2 Examples (1 of 2) H Example 1: TCP Throughput Testing –Simple dumbbell network topology –One-way TCP traffic –Bulk data transfer –Fixed RTT –Bottleneck link has finite DropTail buffer –Throughput is primary metric

11. 11 Some ns-2 Examples (2 of 2) H Example 2: Web Proxy Caching –Hierarchical network topology –Two-way TCP traffic –Web-like data transfers (server to clients) –Heterogeneous RTTs –DropTail router buffers –Response time is primary metric

12. 12 Summary H The ns-2 network simulator is a widely used platform for networking researchers H Large and cumbersome, yet very useful H Good starting point for many projects H Detailed TCP models available H Limited validation of most ns-2 models H Try it if you want!