SIMULATING A MOBILE PEER-TO-PEER NETWORK Simo Sibakov Department of Communications and Networking (Comnet) Helsinki University of Technology Supervisor: Prof. Raimo Kantola

Contents ► Background ► Protocol introductions  SIP, P2PSIP, RELOAD ► Overlay Concept ► DHT  concept  DHT algorithms Chord and Kademlia ► Routing modes ► OverSim simulator ► Input parameters ► Output parameters ► Results ► Conclusions

Background of the study ► The task was to:  simulate a P2PSIP network using RELOAD as its peer protocol  evaluate P2PSIP’s applicability for mobile telephone networks ► The study included:  Writing a C++ class for the simulation program to model the RELOAD messages  Making other necessary additions to the simulation program code.  Collecting and analyzing the results

SIP (Session Initiation Protocol) ► SIP is a signaling protocol used for setting up multimedia sessions ► SIP supports user mobility and localization ► SIP is a traditional client/server protocol dependent on server elements

Location Service 1 REGISTER 5 Response 2 Store 3 INVITE 4 Query ProxyRegistrar 6 INVITE UA domain.com sip.domain.com (public URI) (SIP URI) SIP MESSAGE OTHER PROTOCOL

P2PSIP (Peer-to-Peer SIP) ► An alternative solution to the session establishment ► Provides the same localization service as SIP but without server elements ► Every node (peer) has equal functions and responsibilities for data storage and message routing RELOAD (Resource LOcation And Delivery) ► The peer protocol of P2PSIP ► RELOAD is used for inter-peer communications in the P2PSIP overlay

DHT (Distributed Hash Table) ► Distributes the data and query load evenly to all nodes in the overlay ► Divides the keyspace between the participating nodes ► Each node has an identifier (node ID) ► Stored data elements also have identifiers (resource ID) ► Two DHT algorithms, Chord and Kademlia, are used in this study ► DHT algorithms define the logical location of the nodes in the overlay

Physical links Logical links UNDERLAYING NETWORK OVERLAY NETWORK Overlay concept

Chord ► Nodes are logically arranged in the identifier circle ► Keys are assigned to the node whose ID succeeds the ID of the key ► Chord has two independent routing tables: successor list and finger table

Kademlia ► Nodes are treated as leaves of a binary tree where nodes are located according to the shortest unique prefix of the node ID. ► Every node sees the network as a group of subtrees ► For every subtree a node has a k-bucket in which there is information about k nodes. SUBTREE MODELK-BUCKETS (k=2)

Routing modes SYMMETRIC RECURSIVEITERATIVE

OverSim - Overlay Network Simulator ► Based on OMNeT++ discrete event network simulator ► Consists of modules that are implemented in C++ ► In this study RELOAD was modeled in the DHT TestApp module.

Input parameters ► In the simulations 4 input parameters were observed ► Other parameters were kept fixed ► Altogether 57 simulation scenarios were run ► Simulation time for each simulation run was 14 days

Output parameters ► Overall bandwidth usage ► Message overhead for maintenance  Only when using Chord. Kademlia does not use separate maintenance messages ► Number of lookup hops  Length of the lookup path ► Lookup message overhead  Amount of data transferred in the lookup processes in bytes ► Lookup delay  Delay between sending a lookup and receiving an answer ► Key distribution  Mean number of keys stored per node ► Lookup success rate

► Input paremeters affecting the mean total traffic are number of nodes and key update interval ► Kademlia uses more than twice as much bandwidth than Chord ► Iterative routing uses more bandwidth than recursive routing when Chord is used ► Mean total traffic is generally low (maximum bw for GPRS is ~14kB) Results

Results ► Kademlia needs less time to complete lookups than Chord does ► Kademlia uses more bandwidth for lookup traffic than Chord does

► Kademlia gives higher lookup success rates than chord ► Recursive routing gives higher lookup success rates than iterative routing when Chord is used ► The shorter the key update interval the higher the lookup success rate ► The longer the mean node lifetime the higher the lookup success rate Results

Conclusions ► 2G mobile telephone networks can handle the bandwidht usage of a P2PSIP network using RELOAD peer protocol ► With the input parameters used in this study, lookup success rates are in general too low for session establishment to work satisfyingly. ► Kademlia outperforms Chord when lookup delay and success rates are compared ► Kademlia uses more than twice the bandwidth that chord does. FUTURE RESEARCH: This study could be developed by using more exact input parameters The reasons for the low lookup success rate could be investigated

Questions?