Engineering, Technology & Applied Science Research Vol. 8, No. 3, 2018, 3079-3083 3079 www.etasr.com Halepoto et al.: Analysis of Retransmission Policies for Parallel Data Transmission Analysis of Retransmission Policies for Parallel Data Transmission Imtiaz Ali Halepoto Department of Computer Systems Engineering, Quaid-e-Awam University of Engineering, Science & Technology, Nawabshah, Pakistan halepoto@quest.edu.pk Intesab Hussain Sadhayo Department of Telecommunication Engineering, Quaid-e-Awam University of Engineering, Science & Technology, Nawabshah, Pakistan intesab@quest.edu.pk Muhammad Sulleman Memon Department of Computer Systems Engineering, Quaid-e-Awam University of Engineering, Science & Technology, Nawabshah, Pakistan sulleman@quest.edu.pk Adnan Manzoor Department of Information Technology, Quaid-e-Awam University of Engineering, Science & Technology, Nawabshah, Pakistan adnan@quest.edu.pk Shahid Bhatti Department of Information Technology, Quaid-e-Awam University of Engineering, Science & Technology, Nawabshah, Pakistan shahidmsit12@gmail.com Abstract—Stream control transmission protocol (SCTP) is a transport layer protocol, which is efficient, reliable, and connection-oriented as compared to transmission control protocol (TCP) and user datagram protocol (UDP). Additionally, SCTP has more innovative features like multihoming, multistreaming and unordered delivery. With multihoming, SCTP establishes multiple paths between a sender and receiver. However, it only uses the primary path for data transmission and the secondary path (or paths) for fault tolerance. Concurrent multipath transfer extension of SCTP (CMT-SCTP) allows a sender to transmit data in parallel over multiple paths, which increases the overall transmission throughput. Parallel data transmission is beneficial for higher data rates. Parallel transmission or connection is also good in services such as video streaming where if one connection is occupied with errors the transmission continues on alternate links. With parallel transmission, the unordered data packets arrival is very common at receiver. The receiver has to wait until the missing data packets arrive, causing performance degradation while using CMT-SCTP. In order to reduce the transmission delay at the receiver, CMT-SCTP uses intelligent retransmission polices to immediately retransmit the missing packets. The retransmission policies used by CMT-SCTP are RTX-SSTHRESH, RTX- LOSSRATE and RTX-CWND. The main objective of this paper is the performance analysis of the retransmission policies. This paper evaluates RTX-SSTHRESH, RTX-LOSSRATE and RTX- CWND. Simulations are performed on the Network Simulator 2. In the simulations with various scenarios and parameters, it is observed that the RTX-LOSSRATE is a suitable policy. Keywords-CMT; CMT-SCTP; retransmission policies; SCTP; parallel transmission I. INTRODUCTION The most commonly used protocols of the transport layer of the OSI model are UDP and TCP. UDP is a connectionless and unreliable transport layer protocol. UDP sends data in the form of short messages, which are called datagrams, in a network. UDP is a connectionless protocol, which means that there is no need to establish a connection between the sender and receiver. In terms of reliability, the TCP is the most widely used protocol today. A recently introduced protocol for the transport layer is SCTP, which is reliable and connection-oriented. SCTP is very similar to TCP and UDP in terms of operations. It transmits multiple streams of data simultaneously between two endpoints that have established a connection. SCTP is more efficient and more powerful in its design when compared to peer protocols. CMT-SCTP extension enables a sender to simultaneously transmit data over various paths, which increase the overall transmission throughput. The competitor protocol to CMT- SCTP is multipath TCP, which is also in design phase. Parallel transmission is very common in the development of mobile applications such as video streaming, online gaming, e- commerce, collaborative scientific projects and VoIP, that require faster data transmission and downloading data rate. The parallel transmission through CMT-SCTP uses more than one physical interface, for example the parallel transmission of data between two mobile phones uses two interfaces. One interface transmits using 4G and one interface transmits using WiFi. Sending data through two interfaces increases throughput compared to sending data through one interface. The use of more interfaces also increases the internet availability of a mobile phone. CMT-SCTP is in development process, and some issues such as transmission errors and recovery are challenging. The parallel transmission using CMT-SCTP causes unordered data packet arrival at the receiver. The data travels in parallel through different paths, the data along a fast path may reach the receiver earlier than the data sent along a slow path. To solve the problem an immediate retransmission of the missing data is mandatory for smooth transmission. In order to reduce the transmission delay at the receiver, CMT-