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1. PeerSim (P2P Network)
Sijo Emmanuel & Hein Min Htike

2. What is PeerSim?
● Peer Simulator (PeerSim) is a simulation engine
○ Used to write network protocols for P2P (Peer-to-Peer) networks
○ Scalable (up to 1 million nodes), portable and highly configurable
○ Open source Peer-to-Peer (P2P) system developed using Java
○ Developed at the department of Computer Science in University of Bologna

3. What is a simulation engine?
● An application on top of which we can write simulations, collect results and
analyze them.
● The engine takes care of the temporal structure of the experiment
● The programmer takes care of the logic of the interactions among the
elements of the scenario.
● There are two modes of simulation engines:
● More on next slide!!

4. PeerSim Simulation Engines
● PeerSim has two simulation modes:
● Event-driven: a set of events (messages) are scheduled at different simulation
time and the node protocols are run accordingly to messages’ delivery times.
● Cycle-driven: sequential simulation, in each cycle each protocol’s actions are
executed by every node (we will be focusing on this)

5. Aim
● To create new protocol
○ protocols to find Min & Max in the network
● To explore PeerSim package

6. Objectives
● To create new protocols to generate networks with the maximum and
minimum value.
○ create package for new codes
○ create two classes for Min and Max protocols
○ create observer classes
○ create Max and Min configuration files
○ visualise the topology of the network

7. Key themes/Ideas
● Key theme and idea was to calculate Max and Min values that exists within
the network
● Source of idea - Average function ??
● More on next slides!!!

8. Average Function
● Calculates average between two interacting nodes, and assign that value to
them.
● Perform that computation at every node in each cycle.
● After certain amount of time, all the average values in the network converge.

9. Min/Max Function
● Finds min/max value between two interacting nodes, and assign that value to
them.
● Perform that computation at every node in each cycle.
● After certain amount of time, all the values in the network become (the same)
min/max.

10. Design & Implementation

11. MaxFunction and MinFunction
● Took AverageFunction class as example to create MaxFunction and
MinFunction

12. Observer classes
● Based on AverageObserver, we created two different observer classes
a. node values in the network (NodeValuesObserver)
b. similar to average observer (MaxMinObserver)

13. NodeValuesObserver
● observes the values at each node in all the cycles.
○ to see how the values of the nodes change over time

14. NodeValuesObserver
● same as AverageObserver,
except execute() method,
● use MedianStats Object
○ to print out all the values in
node
○ more about MedianStats in
next slide
● line 111
○ protocol name
○ cycle
● line 112 - 114: print node
values
● line 115: number of nodes

15. MedianStats and IncrementalStats
● included in peersim.util package
● IncrementalStats - keep track of statistics about the network
○ average, min, max, etc.
● MedianStats - extends IncrementalStats
○ can retrieve median element
○ STORE all the elements (ArrayList)
○ we added a getter method to retrieve all the elements

16. MaxMinObserver
● Observe the statistics about the nodes at each cycle
● Same as AverageObserver, except changes to what we want to see in output

17. MaxMinObserver
● same as AverageObserver, except execute() method
● MedianStats is used
● line 112 - prints out only Minimum and Maximum values of the network and no. of nodes

18. Configuration File
● We wrote several configuration files with different components to learn more
about PeerSim.
● Different components we tried will be preseneted in coming slides.

19. Configuration File
● Created configuration files based on Average configuration file for Max and
Min
● simulation.cycles value are
the number of cycles in the
network
● network.size is the size of
the network

20. Configuration File: Protocols
● Created new protocols to run Max and Min functions
● IdleProtocol is the topology of the network which
determines the nodes and degree of network
● aMaxMin.MaxFuntion reads in the Max function and
uses it to find the maximum value in the network
● IdleProtocol serve as a source of neighbourhood
information for other protocols
● It stores links: useful to model a static link-structure

21. Configuration: Linking Nodes
● link nodes to form network
● takes “linkable” protocol, add edges to define topology
● WireKOut: adds random connection
○ Parameter: k - number of edges coming out of each node

22. Configuration: Assigning Values to Nodes
● assign values to the node during initilisation
● ways to distribute values
○ provided in peersim.vector package
○ PeakDistribution
■ parameter: peak - peak value
■ assign peak nodes the peak value, the rest 0
○ LinearDistribution
■ parameter: min and max
■ assign values in the range (min & max) in linearly increasing manner from min to max
○ UniformDistribution
■ parameter: min and max
■ assign values in random from the range (min & max)

23. Configuration: Distribution Examples
Uniform Distribution
Linear Distribution
Peak Distribution

24. Configuration File: Visualisation
● used built-in GraphPrinter control
○ provided in peersim.report package
○ print the whole graph in given format
● two parameters
○ outf - prefix of filename
■ extension - .graph
■ prefix0000001.graph
○ format - format of output graph
■ neighborlist: neighborlist
■ edgelist: one node pair at each line for each edge
■ gml: generic format for many graph tools
● We used Gephi to visualise the graph
○ change file name from .graph extension to .gml

25. Configuration File: Visualisation Example
Example .gml file
Graph visualised in Gephi
Nodes = 1000, k = 10
Edges = 10000

26. Configuration File: Statistics
● Used built-in DegreeStats control
○ provided in peersim.report package
○ statistics about the node degree in graph
● four parameters
○ n: numbers of nodes for sampling degree
○ method: method to print results
■ stats: statistics about degrees of graph (min degree, max degree, average degree, etc.)
■ freq: frequency of degrees of graph
■ list: lists degree of sampled nodes
○ linktype: type of links to print information about (live (default), dead, all)
○ trace: trace the given number of nodes

28. Configuration File: Statistics Example
Example print out to console using stats
Example print out to console using lists & n = 10
Example: freq & n = 25

29. Configuration File: Dynamic Network
● dynamically change the size of network
○ add or remove nodes from the network
● line 31: adds DynamicNetwork control to configuration file.
○ provided in peersim.dynamics package
● line 32: take out 500 nodes from network
● line 33 & 34: when to add/remove nodes from network

30. Results - I
Network size: 10,000
Protocol: MaxFunction
Connection: WireKOut (k=30)
Observer: MaxMinObserver
Dynamic Network: remove 500
from cycle 1 till 5

31. Results - II
Network size: 10,000
Protocol: MinFunction
Connection: WireKOut (k=30)
Observer: MaxMinObserver
Dynamic Network: remove 500
from cycle 1 till 5

32. What have been achieved?
● Created Max/Min functions
● Created two observer classes
● Multiple configurations with different components
● Visualised the graph

33. Observations
● the more the edges, the faster it reaches min/max/average of the network
○ using the same configurations except k;
■ k=10, 20 cycles for all nodes to become minimum value
■ k = 20, 14 cycles for all nodes to become minimum value
■ k = 30, 12 cycles for all nodes to become minimum value

34. Lessons learnt & Conclusions

35. Benefits of PeerSim (P2P Network)
● Portability
○ Possible to reuse simulation code with minor modification
○ Allows user defined entities to replace almost all predefined entities
○ highly configurable
○ Architecture based on extendable and pluggable component features
● Scalability
○ Provides high scalability
○ Can simulate millions of network nodes
○ Can hold up a network up to 106 nodes in the cycle-based model
○ Able to solve problems related to scalability
○ One of the major parameters on which a simulator can be analysed

36. Limitations of PeerSim
● Lacks support for simulating unstructured or semi-structured P2P routing
protocols
● Ability to scale will be reduced if resources are not used efficiently
● Limited support for extending the simulator for protocols other than Bit
○ Difficult to implement other protocols as the simulator is tightly coupled to the Bittorrent
protocol
● No support for distributed simulation
● Simulator makes use of main memory to store visualisation events
○ Limits the system performance in terms of nodes