BitTorrent is one of the Internet's most efficient content distribution protocols. It is known to perform very well over the wired Internet where end-to-end performance is almost guaranteed. However, in wireless ad hoc networks, many constraints appear as the scarcity of resources and their shared nature, which make running BitTorrent with its default configuration not lead to best performances. To these constraints it adds the fact that peers are both routers and end-users and that TCP-performance drops seriously with the number of hops. We show in this work that the neighbor selection mechanism in BitTorrent plays an important role in determining the performance of the protocol when deployed over a wireless ad hoc network. It is no longer efficient to choose and treat with peers independently of their location. A first solution is to limit the scope of the neighborhood. In this case, TCP connections are fast but there is no more diversity of pieces in the network: pieces propagate in a unique direction from the seed to distant peers. This prohibits peers from reciprocating data and leads to low sharing ratios and suboptimal utilization of network resources. To recover from these impairments, we propose an enhancement to BitTorrent which aims to minimize the time to download the content and at the same time to enforce cooperation among peers. Our solution considers a restricted neighborhood to reduce routing overhead and to improve throughput, while establishing few connections to remote peers to improve diversity of pieces. With the help of extensive NS-2 simulations, we show that these enhancements to BitTorrent significantly improve the file completion time while fully profiting from the incentives implemented in BitTorrent to enforce fair sharing.
Paper:
Mohamed Karim Sbai, Chadi Barakat, Jaeyoung Choi, Anwar Al Hamra, Thierry Turletti, "Adapting BitTorrent to wireless ad hoc networks" to appear in proceedings of 7th International conference on ad hoc networks and wireless 2008 (AD-HOC NOW), Sophia Antipolis, France, September 2008. download
The Network Simulator 2 (ns-2) is a popular and powerful simulation tool for the simulation of packet-switched networks, which provides substantial support for simulation of TCP, routing, and MAC protocols over wired and wireless networks, such as wireless LANs, mobile ad hoc networks (MANETs), and satellite communications, etc, and is widely used in both academia and industry. Although many protocol modules have been implemented in the ns-2, the IEEE 802.16 broadband wireless access networks (BWANs) or WiMAX module has not been contributed yet. Thus, in this paper, we present our detailed design and implementation of the WiMAX module based on the IEEE 802.16 standard with the point-to-multipoint (PMP) mode for the ns-2. The implemented module comprises fundamental functions of the service-specific convergence sublayer (CS), the MAC common part sublayer (CPS), and the PHY layer. A simple call admission control (CAC) mechanism and the scheduler are also included in this module.
Installation
To install the patch, follow the instructions below:
The objective of this assignment is to get familiar with the network simulator tool (ns-2) and mobile wireless network environment. This study about ad hoc wireless network will be carried out by simulations using the ns-2 tool. These simulations will be run using Sun workstations of the Birdland (Lintula). The results of the work will be reported in writing.
In this document there are first some are conceptual definitions, instructions for simulations, reporting, grading and returning the report. In the end of this document there are some facts related to implementation details and tips for those who find the required scripting problematic.
Using ns-2
"Ns is a discrete event simulator targeted at networking research. Ns provides substantial support for simulation of TCP, routing, and multicast protocols over wired and wireless (local and satellite) networks." (http://www.isi.edu/nsnam/ns, 18.6.2004) ns-2 is an interpreter of OTcl language, which includes objects for simulating networks. Those objects are implemented using C++, but OTcl is an interface that can be used for calling methods of the objects.
The network topology, transmission and application agents In the picture every circle represents a wireless mobile node. The network consists of TCP source node (n0) and destination node (n1) over an area size of 500m x 500m. Node (n0)uses Agent/TCP/Reno as the sending TCP agent and FTP traffic source. Node (n1) is the receivers of FTP transfers, and it uses Agent/TCPSink as its TCP-agent for the connection establishment.
The routing protocol used for the simulation scenario is ad hoc routing protocol Destination Sequenced Distance Vector (DSDV) and IEEE 802.11 MAC protocol. The targets of the simulation.
In this simulation you will study, the three different wireless network scenario;
TCP connection over two static nodes network. The ns-2 script file 2node_script.tcl (http://www.cs.tut.fi/kurssit/TLT-2756/assign.html) for this wireless network is provided. This creates the topology described earlier, runs the simulation for 150 seconds and shows the TCP window size in two static nodes scenario with DSDV routing protocol. Run the script and analyze the output graph for the given scenario.
TCP connection over 2-nodes (1 mobile and 1 static) network. Use the given script file and change the state of the node (n1) from static to mobile for this second scenario. At time 10 s, node (n1) starts moving towards the point (45, 285) at a speed 5 m/s. The syntax of movement command;
