Supervision : Naceur MALOUCH, Imad MOUGHARBEL

Co-supervision : DIAB Wafaa Bou

Performance Evaluation and Improvement of Congestion Control of the Constrained Application Protocol for the Internet-of-Things

The Constrained Application Protocol (CoAP) is a lightweight core protocol designed by the Internet Engineering Task Force (IETF) used for communication between devices in the Internet of Things (IoT). Congestion control is substantial to overcome the limitations of such devices and the restrictions imposed by the connecting networks. The CoAP standard defines a simple congestion control mechanism based mainly on retransmissions after timeouts and a binary exponential back-off procedure. However, this simple protocol with its default parameters is not sufficient and can dramatically affect the efficiency of CoAP. Several advanced mechanisms for CoAP were suggested by the literature. Some considered improving retransmission timeout estimation whereas others focused on augmenting the retransmission procedure. The improvements in the second part are twofold: The first is Backoff-based such as CoCoA+ and pCoCoA, while the second is rate-based such as BDP-CoAP. We will perform critical analysis of these works and highlight their shortcomings and pitfalls, then present and evaluate our approach in different uses cases and network scenarios.
In this research work, we propose new exact mathematical models to analyze the performance of CoAP in lossy IoT networks. This study provides insights about improving CoAP congestion control in such networks and highlights the properties -- including the limitations -- of CoAP. Besides, we show that the simple control mechanism reduces significantly CoAP performance especially in terms of bandwidth utilization since it prevents the protocol from acting efficiently during congestion periods. We then propose new improvements in order to enhance the trade-off between reliability and goodput while keeping the algorithms reasonably simple for constrained devices. First, we optimize further the estimation procedure of the retransmission timeout in order to enhance congestion detection. Timeouts are the only indicator used in CoAP to detect losses, and losses are used as a strong indicator to detect congestion. Second, we replace the backoff algorithm by "real" congestion control algorithms inspired from the well-known Additive Increase Multiplicative Decrease technique and a recent measurement-based congestion control called BBR. Our analysis using both our simulator and Contiki/Cooja environment show that the rate-based approach outperforms the backoff-based approach. Moreover, all the results show that our algorithms achieve a much better tradeoff between goodput, reliability and overhead.

2019-2022 Publications

• 2022
  • N. Makarem, W. Bou Diab, I. MOUGHARBEL, N. Malouch : “A non-Hidden Markovian Modeling of the Reliability Scheme of the Constrained Application Protocol in Lossy Wireless Networks”, Proceedings of the 25^th International ACM Conference on Modeling Analysis and Simulation of Wireless and Mobile Systems, vol. 25 (1), MSWiM '22, Montreal, Quebec, Canada, pp. 147-156, (Association for Computing Machinery), (ISBN: 9781450394826) (2022)
  • N. Makarem, W. Bou Diab, I. MOUGHARBEL, N. Malouch : “On the design of efficient congestion control for the Constrained Application Protocol in IoT”, Computer Networks, vol. 207, pp. 108824, (Elsevier) (2022)
• 2021
  • N. Makarem : “Performance Evaluation and Improvement of Congestion Control of the Constrained Application Protocol for the Internet-of-Things”, thesis, defence 12/07/2021, supervision Malouch, Naceur Mougharbel, Imad, co-supervision : Diab, Wafaa Bou (2021)
• 2019
  • N. Makarem, W. Bou Diab, I. MOUGHARBEL, N. Malouch : “Performance Study of the Constrained Application Protocol in Lossy Networks”, IFIP NETWORKING 2019, Warsaw, Poland (2019)