Wireless Mesh Networks (WMNs) have emerged to meet a need for a self-organized
and self-configured multi-hop wireless network infrastructure. Low cost infrastructure
and ease of deployment have made WMNs an attractive technology for last mile
access. However, 802.11 based WMNs are subject to serious fairness issues. With
backlogged TCP traffic, nodes which are two or more hops away from the gateway
are subject to starvation, while the one-hop away node saturates the channel with
its own local traffic. We study the interactions of TCP and IEEE 802.11 MAC
in WMNs to aid us in understanding and overcoming the unfairness problem. We
propose a Markov chain to capture the behavior of TCP sessions, particularly the
impact on network throughput performance due to the effect of queue utilization
and packet relaying. A closed form solution is derived to numerically derive the
throughput. Based on the developed model, we propose a distributed MAC protocol
called Timestamp-ordered MAC (TMAC), aiming to alleviate the unfairness problem
in WMNs via a manipulative per-node scheduling mechanism which takes advantage
of the age of each packet as a priority metric. Simulation is conducted to validate our
model and to illustrate the fairness characteristics of TMAC. Our results show that
TMAC achieves excellent resource allocation fairness while maintaining above 90% of
maximum link capacity in parking lot and large grid topologies. Our work illuminates
the factors affecting TCP fairness in WMNs. Our theoretical and empirical findings
can be used in future research to develop more fairness-aware protocols for WMNs.
| Date of Award | May 2011 |
|---|
| Original language | English (US) |
|---|
| Awarding Institution | - Computer, Electrical and Mathematical Sciences and Engineering
|
|---|
| Supervisor | Basem Shihada (Supervisor) |
|---|