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- Basics
Queue (buffer) size allocation at wireless mesh routers is an important configuration parameter that determines network performance characteristics. Small queues lead to packet drops when buffers fill up, degrading network performance. On the other hand, large queues can lead to excessive network delays. In this assignment, you will analyze the buffer utilization for a TCP stream over 802.11-based multihop networks in network simulator ns-2. You may do this assignment in groups of two or individually.
- Getting Started
In this assignment you will be extending the core ns-2 functionality. You will need to understand the architecture of a mobilenode in ns-2, as well as the monitoring and tracing functionality available in ns-2. The ns-2 manual may be a useful starting point. It is available on the web: http://www.isi.edu/nsnam/ns/ns-documentation.html
Another reference for understanding the basic ns-2 architecture is the book 'Introduction to Network Simulator NS2' by Teerawat Issariyakul and Ekram Hossain. It is available online at Springer through KAUST's institutional access: http://www.springerlink.com/content/978-0-387-71759-3
- Assignment
In this assignment, you will analyze the queue utilization of a multihop TCP New Reno stream over 802.11-based WMNs. Nodes at the end of a chain topology experience less contention for channel access than nodes in the middle. One may thus surmise that the average queue utilization at the corner nodes is less than the middle nodes. Understanding this behavior can help us design optimal queue size allocation strategies for WMNs.
In the ns-2 mobilenode architecture, IFq sits between the LL and MAC layer. You will report the average utilization of this queue for source as well as relay mesh nodes over a simulation run. At a minimum, your analysis should include a single TCP flow over a chain topology of varying length. You may simplify your analysis using an equidistant node separation with uniform wireless link rates between the nodes.
The queue monitoring functionality in the base ns-2 distribution is designed for wired networks. e.g., the monitor-queue procedure requires two wired nodes sharing a link to identify the queue between them. If you like, you may extend this functionality so that it is also applicable to the wireless setting with a single shared IFq between a node and its multiple neighbors. You are free to experiment with other design criteria. e.g., an alternative solution may be to log enque/deque/drop operations on this queue object and write them to a trace file.
- Handing In
You will present your main results in a brief presentation (10-15 min) to the class. You are required to submit all the code modified in ns-2. Please also include a README file that briefly describes your implementation and how the proposed monitoring functionality can be invoked using tcl scripts.
- Bonus Consider a chain of wireless nodes with multiple upload or download TCP flows to a gateway node at the end of the chain. For bonus points, report on the queue utilization of various flows from different mesh routers along their routing path.
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