In this paper, we propose Transmission Control Protocol (TCP)-aware cross layer scheduling algorithms in a multipoint-to-point network such as the uplink of an IEEE 802.16 (WiMAX) network. Inadequate bandwidth allocation to a TCP flow may lead to timeout and since TCP source drops its congestion window ( @math ) immediately after a timeout, it may affect the average throughput adversely. On the other hand, since the TCP source increases its @math only linearly upon the availability of bandwidth, any excess assignment of bandwidth may remain underutilized. The proposed scheduling algorithms address this by allocating the resources based on @math and TCP timeout. Moreover, since we focus on uplink scheduling, we consider that only flow level resource requirement is communicated to the Base Station ( @math ) instead of per packet information. The schedulers also take into account the wireless channel characteristics and are thus cross layer in nature. Through exhaustive simulations, we demonstrate that the proposed schedulers exhibit enhanced throughput and fairness properties when compared to that of Round Robin (RR) scheduler under different shadowing. We demonstrate a gain between 3.5 to 15 in throughput and 15 to 25 in channel utilization over RR scheduler under different shadowing.
In @cite_19 , the authors have illustrated the performance of TCP and UDP based applications through rigorous experiments conducted in an IEEE 802.16 deployed network as well as in test-beds. It has been observed that TCP applications suffer significantly as compared to UDP applications if the scheduling scheme does not consider the nature of TCP (TCP parameters). This key observation has encouraged us to work on scheduling schemes which are TCP-aware.
@cite_19
2119994812 2098835300 2101871381 2100166367
In this paper, we focus on various experiments conducted to analyze the performance of Transmission Control Protocol (TCP) and Universal Datagram Protocol (UDP) based applications in a IEEE 802.16 deployed network. We analyze the effect of Medium Access Control (MAC) and Physical layer characteristics on the performance of TCP and UDP-based applications. Our key findings are: (i) throughput achieved by TCP-based applications is lower than that of UDP-based applications, (ii) slot utilization of TCP-based applications is lower than that of UDP-based applications and (iii) throughput of TCP-based applications suffers in the presence of UDP-based applications for similar channel states. We also observe that throughput achieved by both TCP and UDP-based applications with Automatic Repeat ReQuest (ARQ) set in system are higher as compared to that of without ARQ. The findings of these experiments can be adopted while designing efficient scheduling schemes for IEEE 802.16-based network, such that higher throughput, utilization and better delay performance can be achieved. Designing scheduling algorithms that work in synergy with TCP is a challenging problem in wireless networks. Extensive research on scheduling algorithms has focused on inelastic traffic, where there is no correlation between traffic dynamics and scheduling decisions. In this work, we study the performance of several scheduling algorithms in LTE networks, where the scheduling decisions are intertwined with wireless channel fluctuations to improve the system throughput. We use ns-3 simulations to study the performance of several scheduling algorithms with a specific focus on Max Weight (MW) schedulers with both UDP and TCP traffic, while considering the detailed behavior of OFDMA-based resource allocation in LTE networks. We show that, contrary to its performance with inelastic traffic, MW schedulers may not perform well in LTE networks in the presence of TCP traffic, as they are agnostic to the TCP congestion control mechanism. We then design a new scheduler called “Queue MW” (Q-MW) which is tailored specifically to TCP dynamics by giving higher priority to TCP flows whose queue at the base station is very small in order to encourage them to send more data at a faster rate. We have implemented Q-MW in ns-3 and studied its performance in a wide range of network scenarios in terms of queue size at the base station and round-trip delay. Our simulation results show that Q-MW achieves peak and average throughput gains of 37 and 10 compared to MW schedulers if tuned properly. The soft real-time nature of large scale web applications in today's datacenters, combined with their distributed workflow, leads to deadlines being associated with the datacenter application traffic. A network flow is useful, and contributes to application throughput and operator revenue if, and only if, it completes within its deadline. Today's transport pro- tocols (TCP included), given their Internet origins, are agnostic to such flow deadlines. Instead, they strive to share network resources fairly. We show that this can hurt application performance. Motivated by these observations, and other (previously known) deficiencies of TCP in the datacenter environment, this paper presents the design and implementation of D3, a deadline-aware control protocol that is customized for the datacenter environment. D3 uses explicit rate control to apportion bandwidth according to flow deadlines. Evaluation from a 19-node, two-tier datacenter testbed shows that D3, even without any deadline information, easily outper- forms TCP in terms of short flow latency and burst tolerance. Further, by utilizing deadline information, D3 effectively doubles the peak load that the datacenter network cansupport. High-speed networks with large delays present a unique environment where TCP may have a problem utilizing the full bandwidth. Several congestion control proposals have been suggested to remedy this problem. The existing protocols consider mainly two properties: TCP friendliness and bandwidth scalability. That is, a protocol should not take away too much bandwidth from standard TCP flows while utilizing the full bandwidth of high-speed networks. This work presents another important constraint, namely, RTT (round trip time) unfairness where competing flows with different RTTs may consume vastly unfair bandwidth shares. Existing schemes have a severe RTT unfairness problem because the congestion window increase rate gets larger as the window grows ironically the very reason that makes them more scalable. RTT unfairness for high-speed networks occurs distinctly with drop tail routers for flows with large congestion windows where packet loss can be highly synchronized. After identifying the RTT unfairness problem of existing protocols, This work presents a new congestion control scheme that alleviates RTT unfairness while supporting TCP friendliness and bandwidth scalability. The proposed congestion control algorithm uses two window size control policies called additive increase and binary search increase. When the congestion window is large, additive increase with a large increment ensures square RTT unfairness as well as good scalability. Under small congestion windows, binary search increase supports TCP friendliness. The simulation results confirm these properties of the protocol.