Syed Nusrat
Research Scholar, Shri Jjt University
Farman Ali
Research Scholar, Shri Jjt University
Agha Salman Haider
Research Scholar, Manav Bharti University
Download PDFTechnology trends indicate that the future Internet will have a large number of very high-bandwidth links. Less ubiquitous but still commonplace will be satellite and wireless links with high latency. These trends are problematic because TCP reacts adversely to increases in the per-flow bandwidth-delay product. This extended abstract proposes a novel congestion control protocol, called XCP, that outperforms TCP in both traditional and high bandwidth-delay product environments. The problem facing TCP as the per-flow bandwidth-delay increases is multi-fold. First, mathematical analysis of TCP congestion control reveals that, regardless of the queuing scheme, as the delay-bandwidth product increases, TCP becomes oscillatory and prone to instability. By casting the problem into a control theory framework, Low et al. [10] show that as capacity or delay increases, Random Early Discard (RED) [4], Random Early Marking (REM) [2], Proportional Integral Controller [6], and Virtual Queue [5] all eventually become oscillatory and prone to instability. They further argue that it is unlikely that any Active Queue Management scheme (AQM) can maintain stability over very high-capacity or large-delay links. Furthermore, Katabi and Blake [7] show that Adaptive Virtual Queue (AVQ) [9] also becomes prone to instability when the link capacity is large enough (e.g., gigabit links). Inefficiency is another problem facing TCP in the future Internet. As the delay bandwidth product increases, performance degrades. TCP’s additive increase policy limits its ability to acquire spare bandwidth to one packet per RTT. Since the bandwidth-delay product of a single flow over very-high-bandwidth links may be many thousands of packets, TCP might waste thousands of RTTs ramping up to full utilization following a burst of congestion. To address the above problem, we compared a novel protocol for congestion control that outperforms TCP in conventional environments, and further remains efficient, fair, and stable as the link bandwidth or the round-trip delay increases [8].This protocol is eXplicit Control Protocol, XCP, generalizesthe Explicit Congestion Notification proposal (ECN) [12]. Instead of the one bit congestion indication used by ECN, our routers inform the senders about the degree of congestion at the bottleneck. Another new concept is the decoupling of utilization control from fairness control. Methodology In this paper we gives a light to the novel protocol (XCP) for congestion control that outperforms TCP inconventional environments. Conclusion To control utilization, this novel protocol adjusts its aggressiveness according to the spare bandwidth in the network and the feedback delay. This prevents oscillations, provides stability in face of high bandwidth or large delay, and ensures efficient utilization of network resources. To control fairness, the protocol reclaims bandwidth from flows whose rate is above their fair share and reallocates it to other flows. By putting the control state in the packets, XCP needs no per-flow state in routers and can scale to any number of flows. Further, implementation of XCP, requires only a few CPU cycles per packet, making it practical even for high-speed routers
Keywords: Networks; TCP, XCP; Congestion control
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