Improving Congestion Control of TCP for Constrained IoT Networks

For smooth integration with middleboxes on the Internet, TCP (Transmission Control Protocol) is favorably considered as a transport-layer protocol for IoT (Internet of Things) networks. In constrained networks, TCP tends to perform well with a small window size. For example, the uIP (micro IP) TCP/IP stack sets the TCP window size to one segment by default. In such a case, managing the retransmission timer is a primary approach to congestion control. In this paper, we examine the congestion control mechanism of TCP in the uIP stack using grid topology networks. In the preliminary test using the Cooja network simulator, the results show that the original uIP TCP causes lots of retransmissions when a radio duty cycling mechanism such as ContikiMAC is used. One main reason is that, once retransmission is deemed to be necessary, the original uIP TCP sets the retransmission timer based on the fixed RTO (retransmission timeout) before performing a retransmission. Since ContikiMAC may cause large RTT (round-trip time) variations due to the hidden terminal problem, the retransmission timer based on the fixed RTO value may cause lots of retransmissions. To address the problem, we propose a new scheme for managing the retransmission timer which adopts the notion of weak RTT estimation of CoCoA, exponential backoffs with variable limits, and dithering. Simulation results show that our proposed scheme reduces retransmissions while enhancing throughput and fairness when an RDC (radio duty cycling) mechanism is used.

A Method Based on RTO and Selective Acknowledgement for Improving SCTP Protocol Performance in Mobile Ad Hoc Networks

With the increasing development of Mobile Ad Hoc Network usage, there will be more need to have a transport protocol with an appropriate throughput in end to end transport. Because of the design nature of TCP protocol for wired Networks, its application in Mobile Ad-hoc Networks causes a reduction in efficiency, performance and throughput.Protocols such as SCTP with sufficient validity and reliability in data transfer are proposed as solution for increasing throughput. However, in order to provide the above quality, sacrifice factors such as Network balance. In the present paper, two optimized transporting algorithm are introduced. These algorithm act based on retransmission timeout control and selective acknowledgement number for transmissions in SCTP protocol. The offered algorithms using implemented NS-2 simulator and throughput improvement and reduction of packet delay time are compared with former protocols.