Smooth congestion control algorithms
Elvis M. Vieira · 2007
This thesis presents a new congestion control mechanism for TCP denominated SmoothTCP. The objective of this proposal is to have a congestion control mechanism whose performance behavior can be modified by using parameters configured externally. We particularly focus on round-trip time (RTT), fairness, and packet drops, all important performance metrics in various environments, including high-speed networks, multimedia over TCP and wireless. Therefore, we defined SmoothTCP as a subset of congestion control functions. Each one of these functions can have up to five metrics of control configured externally, namely, timeout retransmissions, fast retransmissions, Round-Trip Time (RTT), ICMP-SQ messages and ECN packets. Having defined SmoothTCP as a set of congestion control functions, we described the general behavior of some of its instances such as SmoothTCP-q, SmoothTCP-fxr, SmoothTCP-e, SmoothTCP-rq. In addition, we take a particular instance, SmoothTCP-q, and show its properties related to proactiveness, that is, its characteristics to modify the congestion window size in order to avoid packet drops. Additionally, we show the behavior of SmoothTCp-q involving various connections, particularly concerning to fairness or the capability to share the bandwidth equally among all the connections. We concluded that some instances of SmoothTCP, such as SmoothTCP-q, SmoothTCP-e and SmoothTCP-rq avoid packet drops and can control the maximum Round-Trip Time of a connection if configured correctly. Related to fairness, we concluded that certain configured features of these instances of SmoothTCP influence its fairness and show how to modify them in order to have a more equal bandwidth distribution among all the connections. Keywords. Transport Control Protocol, congestion control and avoidance, network performance, multimedia traffic, quality of service.