OPTIMIZATION IN CONGESTION AT TRANSPORT LAYER

ABSTRACT Existing networks with transport protocols such as TCP and UDP have limitations when fitting into new technologies, like increased heterogeneity and mobility. In order to solve this problem, our attempt is to design a self-adaptive transport protocol, which can fit into the network condition dynamically according to the parameters given by upper layer and the network layer in (wired/wireless) NGN architecture. This paper analyzes the optimization in congestion control mechanisms of nowadays transmission protocols, and does comparison among them in different aspect. We first describe the congestion control mechanism of traditional TCP, and then give out an overview and list the congestion function of transport protocols (such as TCP, UDP, DCCP, SCTP). In the end, we do a simple comparison among all the protocols above, and point out the possible advantages and limitations of these protocols under different transport performances (RTT I INTRODUCTION Recently, the rapid evolution and successful deployment of various emerging wireless technologies,e.g., IEEE 802.11 a/b/g, WiMax, etc., has pushed into a strong demand to integrate numerous wirelesslocal area networks (WLANs) with the existing cellular network infrastructure. The typical example involves the integration of WLAN with Global System for Mobile Communications/General Packet Radio Service (GSM/GPRS), third-generation (3G) Universal Mobile Telecommunications System (UMTS), or cdma2000 networks. The inter-working of such heterogeneous, packet-based radio access networks (RANs), also referred to as next generation or beyond 3G (B3G) mobile data networks[1], poses many technical challenges with mobility managementthat can guarantee service continuity and IP connectivity provision for wireless multi-mode mobile terminals like cellular phones, personal digital assistants (PDAs), and notebook computers, being one of the most important . International Journal Of Advance Research In Science And Engineering http://www.ijarse.com IJARSE, Vol. No.2, Issue No.7, July, 2013 ISSN-2319 145 | P a g e www.ijarse.com Earlier works on the mobility management problem in heterogeneous networks discussed solutions in various layers of the International Organization for Standardization Open Systems Interconnection Basic Reference Model (ISO/OSI model) of the protocol stack where the mobility can be handled: application, transport, and network and data-link layer, respectively. In terms of challenges present in heterogeneous networks, transport layer seems a feasible candidate to host seamless mobility management. Nevertheless, the vast majority of the new mobilityrelated proposals seem to follow most of the existing schemes and stick to mobility handled at the network layer. In the last few years several research efforts have been devoted to study the performance of both TCP and UDP over wired, wireless, and heterogeneous network scenarios. Recently, the Stream Control Transmission Protocol (SCTP) and the Datagram Congestion Control Protocol (DCCP) have attracted the attention of the research and industry communities DCCP is a fairly new unreliable datagrams transport protocol that provides a congestion-controlled flow. DCCP should make easy to deploy delay-sensitive application, without risking congestion collapse.Datagram Congestion Control Protocol (DCCP) is an un-reliable transport layer protocol that provides congestion control on datagrams innetwork.It has support for Explicit Congestion Notification (ECN) In this paper, our main objective is to optimize in the different congestion control mechanisms of the existing protocols and finding out how they affect the performance in different aspects. In section 2, the traditional transmission control protocol (TCP) would be presented as an example to explain how congestion control mechanism works. Section 3 to section 4, list some other transport protocols used nowadays and describes their main features, including the motivation, congestion algorithm, advantages and limitations. The future research and conclusion is given in Section 5. II CONGESTION CONTROL MECHANISM OF TCP The transport layer flow control as any scheme by which the transport sender limits the rate at which data assent over the network (a) preventing a transport sender from sending data for which there is no available buffer space at the transport receiver, or (b) preventing too much traffic in the underlying network. Flow control for (b) also is called congestion control, or congestion avoidance. Congestion is essentially a network layer problem, and dozens of schemes are discussed and classified. In TCP, there is a congestion window (cwnd) which determines the number of bytes that can be sent out at any time. This is used to prevent the physical link between two end points from getting overloaded with too much traffic. The sending rate should always be under the size of the congestion window. TCP uses a slow-start mechanism at the beginning when association established. For initializing the connection, every Route Trip Time, cwnd= cwnd+ 1, which is exponential growth. Although it's International Journal Of Advance Research In Science And Engineering http://www.ijarse.com IJARSE, Vol. No.2, Issue No.7, July, 2013 ISSN-2319 146 | P a g e www.ijarse.com called slow-start, actually it is not slow anymore. As we can see, through slow-start, the congestion window can reach to a large value quickly, but obviously it cannot keep growing When the size of congestion window has reached the value, it comes into the congestion control session. In this session, if all segments are received and the acknowledgments reach the sender on time, the window size will increase steadily but slowly. The window keeps growing linearly until a timeout occurs or the receiver reaches its limit. If a timeout occurs, the window size will drop dramatically. For congestion control algorithm, TCP use: III DATAGRAM CONGESTION CONTROL PROTOCOL (DCCP) DCCP is a connection oriented and un-reliable transport layer protocol. Many other transport protocols appear in order to fit into different usages and vary with network physical conditions, especially for the high bandwidth delay product network. In the following sections we analyze some of the most well-known protocols so as to do the comparison in the discussion part. Motivation Fast-growing Internet applications including streaming media, telephony and interactive games need new requirements of network protocols. Most of them prefer timeliness to reliability. One special requirement of those applications is that they are extremely sensitive to delay and quality fluctuation. On the other hand, losing a certain number of packages would not affect the quality of service International Journal Of Advance Research In Science And Engineering http://www.ijarse.com IJARSE, Vol. No.2, Issue No.7, July, 2013 ISSN-2319 147 | P a g e www.ijarse.com Overview DCCP is a unicast, connection-oriented transport protocol with bidirectional data flow. It provides built-in congestion control, including Explicit Congestion Notification (ECN) support Different from UDP, DCCP connections start and end with three-way handshakes, and the 16-byte generic header which datagrams begin with is shown i