Transmission Control Protocol Flow Control Research Articles

Proposal of cross‐layer bandwidth assignment with buffer size indication for TCP flow control

AbstractIn this paper, we propose, verify, and evaluate a method combining cross‐layer method and bandwidth allocation to overcome the difficulty of flow control in a network with large bandwidth delay product. When the bandwidth delay product is large, there are problems with the convergence time, efficiency and stability of bandwidth utilization, and fairness among traffics of different round‐trip time. As a result of examining the conventional methods, we propose a novel method that can be realized as a functional addition to the existing transmission control protocol (TCP) flow control with improvement in utilization efficiency, fairness, stability, and convergence time. The method is compared with TCP Reno, FAST TCP, CUBIC, Explicit Congestion Notification, and eXplicit Control Protocol by simulation, and is confirmed as having good characteristics.

Different Issues and Survey of Proposed Solutions in TCP over Wireless Environments

Abstract— Computer networks have experienced an explosive growth over the past few years, which has lead to some severe congestion problems. Reliable protocols like TCP works well in wired networks where loss occurs mostly because of congestion. However, in wireless networks, loss occurs because of bit rates and handoffs too. TCP responds all losses by congestion control and avoidance algorithms, which results in degradation of TCP’s End-To-End performance in wireless networks. This paper discusses different issues and problems regarding use of TCP in wireless networks and provides comprehensive survey of various schemes to improve performance of TCP in Wireless Networks. Keywords—TCP, Mobile-IP, Wireless networks, Protocol design. I. INTRODUCTION Due to rapid advances in the area of wireless communications and the popularity of the Internet, the provision of packet data services for applications like e-mail, web browsing, mobile computing etc. over wireless is gaining importance. The TCP/IP protocol suites have number of layers, of which transport layer is used widely for mobility. It uses protocols like TCP and UDP for transferring data. While coming towards wireless environment, we must understand what wireless environment is first. Wireless environment can be broadly distinguished in three types: Cellular networks, Ad-hoc networks and Satellite networks. In Cellular Networks a mobile host is connected to the fixed network with the help of the Base Station. This is the most common form of Wireless Network currently in use. Mobile devices like cell phones, laptops use this network. Most of the proposed solutions to TCP use this model. All service providers are on the fixed network and hence we have to address the problem of wireless networks only at one end point. Ad – Hoc Networks are formed by mobile hosts which are connected to each other within a radio distance. This kind of a model is not well deployed and very few solutions have been proposed to this model. Satellite Networks are those where a satellite link is in between the sender and the receiver. These have very high BERs (Bit Error Rates) and high latency because the Satellite are at a great distance from the surface. Now going towards our main concept, Transmission Control Protocol (TCP) [1] is one of the important standards in the internet world and also a very vital element in internet protocol suite. It provides a connection oriented service with reliable data transfer over the unreliable underlying protocols. It uses sequence numbering and timers to ensure reliable transfer of packets. TCP's flow control increases the data sending rate until there are signs of congestion in the network. The basis of TCP congestion control lies in the following algorithms: slow start, congestion, avoidance, fast retransmit and fast recovery [2]. In the following we first outline the different issues of TCP in wireless networks. Then the main problem regarding TCP. Then we summarize some proposed solutions with their strengths and weaknesses. II. I

Engineering TCP transmission and retransmission mechanisms for wireless networks

Transmission Control Protocol (TCP) provides mechanisms for reliable data communications. Although it works well in wired networks, it fails to offer satisfactory performance in lossy and wireless environments. And in the multi-hop wireless infrastructure, packet delivery suffers high cumulative loss rate if traveling over multiple wireless hops. The Selective acknowledgment (SACK) is one header option that might be used to combat segment corruptions in air channels. In this paper, an alternative set of flow control mechanisms is proposed to handle high packet loss rate in a wireless medium. Using a measurement-based mechanism, sustainable segment delivery is achievable through a novel size-reduction method. Multiple segment retransmission mechanisms are introduced to reduce successive timeout events. One single byte loss is sufficient to waste all other bytes in a file received at a destination. That is, a good TCP flow control mechanism should provide a high successful file transmission completion rate, and this is set as our design goal. Through thorough simulations, our proposed multi-segment retransmission designs perform with higher successful file transfer rate and fewer timeout events than NewReno and SACK under a wide range of packet loss probabilities.

A modification of TCP flow control for improving end-to-end TCP performance over networks with wireless links

End-to-end Transmission Control Protocol (TCP) performance is one of the more important issues in wireless Internet services. This paper proposes the improvement of end-to-end TCP performance via a TCP-aware link layer protocol called Adaptive TCP (A-TCP). The key idea behind the protocol is that an A-TCP agent, which is located in each base station, makes a mobile host look as if it has a wired link with the base station. This concept is referred to in this paper as the virtual host model. In order to implement this model, the A-TCP agent performs three functions: local retransmission, sender freezing and A-TCP flow control. A-TCP flow control is an original proposal and is also the principal factor for improving end-to-end TCP performance in a wireless Internet environment. In A-TCP flow control, the A-TCP agent marks the window field of each acknowledgment segment with a retransmission buffer size. Therefore, the TCP congestion controls, which happen in a TCP sender, are not caused by wireless link overflow. Performance evaluations were conducted via computer simulations and mathematical analyses. The results of the evaluations show not only that the A-TCP improves end-to-end TCP performance by at least 20%, which is higher compared to other TCP approaches, but also that the A-TCP can provide near-optimal performance in wireless bottleneck conditions. In addition, this paper proposes an A-TCP agent architecture, which consists of virtual host objects and several other functional blocks, and describes a new hand-off policy for the virtual host model, called transport-level soft hand-off.

Mobility support in hybrid wireless/IP networking

The ramifications of Transmission Control Protocol (TCP)/Internet Protocol (IP) networking with mobile hosts and wireless links in a hybrid wireless/IP environment are examined. Two issues that affect the performance of TCP/IP are mobility support in the network layer and coping with packet errors in TCP flow/congestion control in the transport layer. The operational features of agent-assisted, router-oriented and hybrid strategies for mobility support are identified and discussed. Packet errors due to transmission through the wireless channel and handover induced by user mobility can pose problem for the conventional TCP flow control in the transport layer. Strategies to cope with errors in packets that enter the TCP connection are described and discussed.