SCTP vs. TCP Delay and Packet Loss Afzall, Aman-Ullah-Khan', Yousaf Bin Zikria3, Salvatore Loreto4 Computer Science Daprtment CIIT,Wah Cantt1, Universit a di Napoli "Federico II" Naples (Italy)2 Electrical Engineering Department CIIT,Islamabad3, Salvatore Loreto Ericsson Research Jorvas, Finland4 khalil_78_pk@yahoo.com1, auk_pk@yahoo.com1, pescape@unina.it2, yusi 2@hotmail.com3, salvatore.loreto@ieee.org4 Abstract- Stream control Transmission protocol (SCTP) is a new transport layer protocol, proposed by IETF in RFC 4960. In this paper we have done a simulation-based comparison of important Quality of Service parameter delay and the impact of packet loss on the throughput using SCTP and TCP Sack as a transport protocol in network simulator (ns-2) in wired network. Our result shows that SCTP and TCP Sack show similar behavior in term of delay in single flow and competing traffic while SCTP achieves higher throughput than TCP when different loss probability is induced in the network. Keywords-SCTP; TCP SACK; Cwnd; Rwnd; Ack; I. INTRODUCTION In this paper we have investigated a comparison of delays offered by SCTP and TCP SACK, and the impact of packet loss on throughput when carrying FTP traffic with varied loss probability. TCP has been the exclusive dominant reliable transport protocol on the internet even to date. Although a lot of research has been carried out regarding transport protocol redesign and reengineering, but it has not swayed the dominance of TCP to a great extent. Still the transport protocols like SCTP and others are still stirring in the research community and nowadays are going to become a regular part of the TCP/IP protocol suite in popular operating systems. SCTP was presented by the IETF SIGTRAN Working Group to transport SS7 signaling traffic on the Internet. At present the SCTP standardization work is continuing in the IETF TSV (Transport Area Working group). Even if the original aim was a protocol for transport signaling the research has taken a giant leap in terms of proposing SCTP has a perspective transport for carrying FTP as well as web traffic. Amer et al. have carried out major research activities in this regard. They have done investigation of SCTP for carrying web and FTP traffic. In [1] they propose it as a state-of-the-art transport protocol for web, whereas in [2] they have talked about concurrent multi-path transfer using multi-homing feature of SCTP, retransmission policies for this scenario [3], and effect of receiver buffer [4] .The stress in this work has been the calculation of one-way delay and the impact of packet loss on the performance of both TCP Sack and SCTP. The rest of the paper is organized as follow. In section II we have dilated about some of the research efforts carried out in the perspective related to our work. Section III makes conspicuous some of the key features of SCTP. In section IV we summarize the TCP SACK. In Section V we narrated our simulations work. And finally in Section VI we conclude our work. II. RELATED WORK In case of the wired scenario, authors in [5] presented results related to the experimentation of the SCTP over high-speed wide area networks. In [6] the authors compare the performance of SCTP and TCP with respect to Web traffic. In [7], using ns-2, the authors study the multi-streaming and the multi-homing SCTP features. They prove that these aspects have advantages over TCP in the given scenarios. In particular, they define the optimal number of streams in multi-streaming and explain how it affects network performance. In the case of wireless networks, in [8] the authors developed an analytical model that takes into account the congestion window, the round trip time, the slow start and congestion avoidance processes to predict the SCTP performance. By comparing numerical results from the analytical model with simulation results, they demonstrate that the proposed model is able to accurately predict SCTP throughput. And finally in [9] the author measure SCTP throughput and Jitter over heterogeneous networks in a real environment and present a packet level analysis of SCTP in wired, wireless and heterogeneous scenarios. Our work is an extension of [9] to measure the packet delay and impact of packet loss on throughput using TCP Sack and SCTP as a transport protocol. III. OVERVIEW OF SCTP The Stream Control Transmission Protocol (SCTP) [10] is a transport protocol designed to transport signaling traffic. SCTP inherits its congestion and flow control mechanisms from TCP, and includes a number of refurbishments intended to make it a more efficacious signaling transport than TCP. In general the main differing facets that SCTP has are: multistreaming (i.e. multiple logical paths per association with optional unordered delivery avoiding one of the primary TCP problems Head-of- Line Blocking), multihoming (multiple network interfaces out of witch one is chosen as primary), four way connection establishment (avoiding SYN Denial-of-Service attacks) and message orientation (making the job of the application parser easier by negating the requirement of application level framing) 1-4244-1553-5/07/$25.00 ©2007 IEEE