An XML Front-End for ns-3

1. An XML Front-End for ns-3 George Riley and Josh PelkeyGeorgia Institute of Technology

2. Overview • Motivation • Approach • Details of XML interface • Problems with the Approach • Alternative Approaches • Summary

3. Motivation • A primary effort from the NSF funding for ns-3 is “educational use”. • The ns-3 simulator requires tools for compiling, linking, and in some cases C++ programming skills. • The majority of classroom educators at college level, either at undergraduate or graduate level are unlikely to have these compiling/linking tools readily available, and are not in fact skilled in these areas. • Often rely on undergraduate or graduate “teaching assistants”, who may or may not have programming skills. • In order to promote “educational use”, we must have a simple way, using tools that are readily available to nearly all users (eg. Text editor)

4. Approach • Describe the ns-3 simulation scenario using the well-known Extensible Markup Language (XML). • Implement an XML parser that both understands the XML syntax, and the meaning of the ns-3 objects specified • The XML parser will read the complete XML file, validate that it is correct, then create the ns-3 objects (nodes, links, protocol stacks, routing objects, and applications) • The parser will produce meaningful and detailed error messages when erroneous specifications are detected. • Allows command line arguments to vary independent variables, to illustrate effects of network parameters. • A difficulty is that the XML syntax is not easily adapted to concepts such as loops, repetitions, and references to other XML elements

5. Details of XML Interface • The XML root element is the ns3 element • Attribute “StopAt” • Subelements: • cmdline • randomgenerators • topology • applications • animation • statistics

6. cmdline element • Attributes are: • name • Name of ns-3 attribute • default • Default value if not specified • help • Help text

7. randomgenerators element • Subelements • exponential • Name • Mean • limit • Uniform • Name • Min • Max • Normal • Name • Mean • variance • Constant • Name • Value

8. randomgenerators example • <randomgeneratorsrunNumber = "$runNumber" seed = "123456" > • <exponential name = "exp1" mean = "1.0" limit = "100.0" /> • <uniform name = "uni1" min = "0.0" max = "1.0" /> • <normal name = "norm1" mean = "0.0" variance = "1.0" /> • <constant name = "const1" value = "0.0" /> • </randomgenerators>

9. Topology Element • Attributes • autoIPV4 • GODRouting • NIXRouting • autoIPV4Base • autoIPV4mask • Subelements • Queue element • P2plink element • Node element • Connect p2p • Dumbbell

10. Applications Element • Subelements • Onoff • Constantbitrate • Bulksend

11. Statistics Element • Log subelement, attributes: • Repeat • Name • Stat • At • Frequency • Example: • <log repeat = "10" name = "sinkRx" stat = "$packetsinkapp$0$totalBytesRx" at = "1.0" frequency = "1.0" />

12. Problems with this Approach • Windows! • The vast majority of teaching faculty use windows. We will have to have a windows versio • John Abraham has already ported most of ns-3 to the win32 API • Animation! • Not only topology and packets, but various metrics (queue occupancy, sequence number for TCP, etc) • Still need detailed understanding of how ns-3 pieces fit together • Lack of “real-time” statistics (ie. Queue occupancy over time as simulation is running). • Requires new code in ns3xml for each release (with new topology, applications, queues, etc).

13. Alternative Approaches • Drag and drop GUI • Still need some “save file format”, so perhaps the drag and drop GUI could produce ns3xml format. • Pre-compile many “scenarios” and use command line arguments for setting independent variables. • Presupposes we an predict in advance all possible teaching scenarios. Seems unlikely

14. Summary • Ns3xml is still work in progress • Usefulness and ease of use in the classroom is yet to be demonstrated • Proof is in the pudding. • We will monitor when and if other teaching faculty download and use ns3xml