The difference in TCP and UDP results is due to the flow control mechanism of TCP.

1. Priority Queuing : Achieving Flow 'Fairness' in Wireless Networks I One hop 0 3 1 2 2 1 2 0 Two hop 5 4 T2 T1 I Routing Packets Queue 0 Own Packets Queue 1 Others’ Packets Queue 2 Q1 Q1 Q1 Q2 Q2 Q2 0 2 ROUTING ROUTING ROUTING 2 1 3 3 Internet Figure1 In a wireless mesh network, routers are connected wirelessly as shown in Figure 1. 3 Flows 1 Traffic from end-users travel through different routes as shown above. The different lengths and contention along each route affects performance of the flows. Routes that service multiple flows are places where prioritization strategies can be utilized to adjust performance. T I 0 2 • Typical Queuing Methods • First-In-First-Out (FIFO) • Packets serviced depending on arrival time. • Strict Priority • Packets placed into different queues according to some criteria (type, source…) • Service queue A, unless it’s empty. Then service queue B, and so on. • Weighted Fair • Packets placed into different queues according to some criteria (type, source…) • Service queue i for xi fraction of the time where • and T = total number of queues. Priority Queuing Achieving Flow 'Fairness' in Wireless Networks Thomas Shen, University of Illinois-UC and Dr. K.C. Wang, Clemson University Our Priority Strategy Figure8 UDP flows are 200Kbps CBR traffic Quad Chain • Use a combination of strict priority and weighted fair queuing • Motivation • Wireless networks of many different topologies are in use today for anytime, anywhere access • Multiple user accesses contend for network resources • Contention is primarily arbitrated in medium access control (MAC) and network scheduling • At each individual node, the network layer allocates the share of transmission time given by the MAC layer to different flows • To control QoS of contending flows, the project exploits priority queuing methods for network scheduling MAC layer If packets exist Queue 0 Threshold 1 Threshold 2 else Pitfalls TCP throughput for multi-hop traffic on the quad chain and small mesh were terrible Lack of MAC access prevents packets from being sent With few packets, queuing method has no effect IEEE 802.11 MAC protocol is not efficient for multi-hop networks as documented in literature If packets exist Queue 1 Probability 1-p Figure2 • Categorize packets based on packet type and source. If packets exist Queue 2 Probability p Figure3 • Service routing packets first, since routes needs to be established before other packets can reach their intended destination For example, the packet assignment for the triple chain UDP scenario is shown in Figure4. Figure9 Figure4 Thresholds T1 and T2 were both varied. T2 controls Flow 1 and 2. At T2 = 0.5 , UDP flows 1 and 2 got the same end-to-end rate. • Simulation Setup • Types of traffic • Constant Bit Rate traffic over UDP. • UDP is unreliable, one way traffic • FTP traffic over TCP • TCP is reliable two way traffic with flow control • Performance Metrics • Calculate end-to-end throughput for TCP • Calculate end-to-end success rate for UDP • Assumed error-free transmission • Link rate: 1Mbps • Five trials each Simulations Threshold is set equal to the probability of servicing others’ packets before your own. Small Mesh Figure10 Figure11 Triple Chain Threshold UDP flows are 200Kbps CBR traffic Figure5 Threshold changed for all intermediate nodes. The difference in TCP and UDP results is due to the flow control mechanism of TCP. UDP flows are 100Kbps CBR traffic Threshold change allocated bandwidth between Flow 2,4 and 5. Other flows were unaffected due to lack of serious contention. • Future Work • Implement different priority assignment strategies • Identify potential objectives to guide priority assignment • Ensure throughput regardless of route length by categorizing according to hops • Ensure throughput of certain users by categorizing according to source • Ensure throughput of certain applications by categorizing accord to packet type. • Devise a performance criteria to evaluate fairness • Conclusion • Results show throughput is unbalanced using FIFO • Priority queuing allocates bandwidth among flows • In our simulations, thresholds of 0.5 to 0.7 distributed throughput most equally SURE 2005 Figure7 Figure6