Congestion Control Algorithms for the Constrained Application Protocol (CoAP)

The Internet of Things (IoT) consists of physical devices, such as temperature sensors and lights, that are connected to the Internet. The devices are typically battery powered and are constrained by their low processing power, memory and low bitrate wireless communication links. The vast amount of IoT devices can cause heavy congestion in the Internet if congestion is not properly addressed. The Constrained Application Protocol (CoAP) is an HTTP-like protocol for constrained devices built on top of UDP. CoAP includes a simple congestion control algorithm (DefaultCoAP). CoAP Simple Congestion Control/Advanced (CoCoA) is a more sophisticated alternative for DefaultCoAP. CoAP can also be run over TCP with TCP's congestion control mechanisms. The focus of this thesis is to study CoAP's congestion control. Shortcomings of DefaultCoAP and CoCoA are identified using empirical performance evaluations conducted in an emulated IoT environment. In a scenario with hundreds of clients and a large buffer in the bottleneck router, DefaultCoAP does not adapt to the long queuing delay. In a similar scenario where short-lived clients exchange only a small amount of messages, CoCoA clients are unable to sample a round-trip delay time. Both of these situations are severe enough to cause a congestion collapse, where most of the link bandwidth is wasted on unnecessary retransmissions. A new retransmission timeout and congestion control algorithm called Fast-Slow Retransmission Timeout (FASOR) is congestion safe in these two scenarios and is even able to outperform CoAP over TCP. FASOR with accurate round-trip delay samples is able to outperform basic FASOR in the challenging and realistic scenario with short-lived clients and an error-prone link

Sender-driven bandwidth differentiation for transmitting multimedia flows over TCP.

Lau Kwok Hung.Thesis (M.Phil.)--Chinese University of Hong Kong, 2006.Includes bibliographical references (leaves 66-67).Abstracts in English and Chinese.Acknowledgement --- p.1Abstract --- p.2摘要 --- p.3Chapter Chapter 1 --- Introduction --- p.6Chapter Chapter 2 --- Background and Related Work --- p.9Chapter 2.1 --- Application-Layer Bandwidth Differentiation --- p.9Chapter 2.2 --- Related Work --- p.14Chapter 2.2.1 --- Bandwidth Differentation --- p.14Chapter 2.2.2 --- Shared Congestion Management --- p.15Chapter 2.2.3 --- Flow Partition --- p.16Chapter Chapter 3 --- VPS Protocol Architecture --- p.17Chapter 3.1 --- Virtual and Actual Flows --- p.18Chapter 3.2 --- VPS Controller --- p.21Chapter Chapter 4 --- ACK Translation --- p.25Chapter 4.1 --- Fast Retransmit and Fast Recovery --- p.27Chapter 4.2 --- Timeout --- p.30Chapter 4.3 --- Packet and ACK Reordering --- p.33Chapter 4.4 --- False Duplicate ACK Suppression --- p.35Chapter 4.5 --- Maxburst --- p.37Chapter 4.6 --- Memory Overhead and Computation Complexity --- p.38Chapter Chapter 5 --- Bandwidth Differentiation --- p.41Chapter 5.1 --- Distribution of Virtual Packets --- p.41Chapter 5.2 --- Temporary Suspension of Actual Flows --- p.43Chapter 5.3 --- Receive Window Limit --- p.44Chapter 5.4 --- Limited Data Transmission --- p.44Chapter Chapter 6 --- Performance Evaluatoin --- p.45Chapter 6.1 --- Performance Metric --- p.45Chapter 6.2 --- Simulation Setup --- p.46Chapter 6.3 --- Performance over Different Time Scales --- p.47Chapter 6.4 --- Performance over Different Bottleneck Bandwidth --- p.53Chapter 6.5 --- Performance over Different Application-specified Ratios --- p.54Chapter 6.6 --- Performance over Different Number of Flows --- p.57Chapter 6.7 --- Heterogeneous Receivers --- p.60Chapter Chapter 7 --- Conclusions and Future Work --- p.65Bibliography --- p.6

Study of TCP Issues over Wireless and Implementation of iSCSI over Wireless for Storage Area Networks

The Transmission Control Protocol (TCP) has proved to be proficient in classical wired networks, presenting an ability to acclimatize to modern, high-speed networks and present new scenarios for which it was not formerly designed. Wireless access to the Internet requires that information reliability be reserved while data is transmitted over the radio channel. Automatic repeat request (ARQ) schemes and TCP techniques are often used for error-control at the link layer and at the transport layer, respectively. TCP/IP is becoming a communication standard [1]. Initially it was designed to present reliable transmission over IP protocol operating principally in wired networks. Wireless networks are becoming more ubiquitous and we have witnessed an exceptional growth in heterogeneous networks. This report considers the problem of supporting TCP, the Internet data transport protocol, over a lossy wireless link whose features vary over time. Experimental results from a wireless test bed in a research laboratory are reported