Mean Waiting Delay for Web Object Transfer in Wireless SCTP Environment Abstract-Most current web application use HTTP (Hyper Text Transfer Protocol) and TCP (Transmission Control Protocol) to retrieve objects from the Internet. SCTP (Stream Control Transmission Protocol) is recently proposed transport protocol with congestion control mechanism similar to that of TCP. Waiting delay is an important performance criterion for when transferring web object over the Internet. In this paper, we present an analytical model of mean waiting delay for object transfers over the Internet in a wireless using the SCTP as the transport protocol and compare with the mean waiting in using TCP. Validation of the model using experimental results show that the mean waiting delay for HTTP over SCTP is less than that for HTTP over TCP. This is caused by the small slow-start time of SCTP. I. INTRODUCTION Most web applications use HTTP (hyper text transfer protocol) as the transfer protocol to retrieve objects in the Internet. HTTP is a connection-oriented protocol and uses TCP (transmission control protocol) as the transport layer protocol. TCP provides a single stream of data and strict ordered delivery. Consequently, when a packet is lost in the network, all subsequent packets arriving at the receiver must wait until the lost packet has been retransmitted from the sender and received at the receiver. This phenomenon, called Head of Line (HOL) blocking, results in waiting delay [1] that affects the performance of web transfers. SCTP (Stream Control Transmission Protocol) [2,3,4] has been proposed by IETF as a new transport layer protocol. The design of SCTP absorbed many strengths of TCP, such as window-based congestion control, error detection, and retransmission. Moreover, SCTP incorporated several new features that are not available in TCP. Two main new features are multi-streaming and multi-homing. SCTP’s multi- streaming can alleviate the head-of-line blocking when an HTML page contains multiple objects. However, it cannot avoid the waiting delay between packets when single objects are transferred; the end point must hold the received packet from delivery to the upper layer protocol (HTTP) until they are reordered. This waiting delay is affected by slow-start and retransmission policy. Several models [5,6,7] that estimate the mean transfer times of TCP application have been presented in the literature; however, they assumed single packet loss. Furthermore, since the waiting delay was not considered in the transfer time, we cannot extract the waiting delay from the previous models. The objective of this paper is to develop an analytical model to estimate the waiting delay for multiple packet losses when SCTP is used in a wireless web environment and compare with the mean waiting delay of TCP. The rest of the paper is organized as follows. Section 2 provides background on the web object transfer in TCP and SCTP environment. Section 3 describes the mean waiting delay time in web object transfer. Section 4 presents mean waiting delay comparison of HTTP over TCP and HTTP over SCTP. Finally, concluding remarks are given in Section 5. II. WEB OBJECT TRANSFER IN TCP AND SCTP ENVIRONMENT Consider the simple case of a web browser displaying a web page with embedded objects. Using HTTP/1.1 that supports persistent and pipelined connections, the browser opens a new transport connection to the server, and sends an HTTP GET request with the desired URI (Uniform Resource Identifier). The request may consist of a specific command, a message containing request parameters, information about the client and may contain URI’s of embedded objects. The server returns an HTTP response with the page contents. The response includes status information, a success/error code, and a message containing information about the server and information about the response itself. As responses arrive from the server, the browser displays the web page with its embedded objects. In general, objects embedded within a web page are independent of each other. That is, requesting and displaying each object in the page does not depend on the reception of other embedded objects. This leads to HOL blocking problem that causes performance degradation. To alleviate HOL blocking, web browsers usually open multiple TCP connections to the same web server. Using multiple TCP connections for transferring a single application's data introduces many negative consequences for both the application and the network. It may cause the increased load on web server. Under high loads, some web servers may choose to drop incoming TCP connection requests due to lack of available memory resources. The other drawback is increased connection establishment latency. Each TCP connection goes through a three-way handshake for Yong-Jin Lee 1 and M.Atiquzzaman 2 1 Department of Technology Education, Korea National University of Education 2 School of Computer Science, University of Oklahoma This full text paper was peer reviewed at the direction of IEEE Communications Society subject matter experts for publication in the IEEE ICC 2009 proceedings 978-1-4244-3435-0/09/$25.00 ©2009 IEEE