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Zeta-TCP refers to a set of proprietary TCP algorithms targeted to improve the end-to-end performance of TCP, regardless of whether the peer is Zeta-TCP or any other TCP protocol stack, in other words, to be compatible with the existing TCP algorithms. It was designed and implemented by AppEx Networks Corporation. Zeta-TCP offers the following improvements primarily: * Congestion avoidance based on both latency and loss measures. * Improved loss-detection algorithm. * Reverse control. == Congestion Avoidance == Most of the TCP stack implementations today use TCP New Reno or its variations (such as TCP SACK (RFC3517 )) as the congestion avoidance algorithm. The New Reno based algorithms are loss-based. Loss-based algorithms treat the packet losses as the sole indication of the congestions in the network. As the Internet has since evolved, this assumption is often an overkill today. The congestion loss is constantly descending with the advancement of the technologies, while, relatively, random loss due to the properties of the media (e.g., wireless/Fading channels), wireline noises/cross-talk, connectivity flaws, software bugs, etc., is increasing. Once a "congestion" is detected (or false-alarmed), New Reno shrinks the Congestion Window (CWND) sharply, causing a plunge of the sending rate. This is one of the major reasons that the TCP based applications are often barely able to utilize a fraction of the subscribed bandwidth today, especially when the RTT is large. TCP Vegas and its variations, most notably FAST TCP, base their congestion prodications on the RTT measurement only. Such latency-based algorithms overcome the problems of the loss-based ones, and are usually a more realistic reflection of the congestions in the network. But the latency-based algorithms have their own limitations, too. Zeta-TCP attempts to tackle the problem by combining the strength of both latency-based and loss-based algorithms. It constantly measures the RTT variation and loss rate variation, and calculates the likelihood of the congestions. Different CWND backoff schemes are applied based on the likelihood level. With the highest level, it applies the backoff scheme of New Reno, which has already been proven to be effective and stable with many years of massive deployment. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Zeta-TCP」の詳細全文を読む スポンサード リンク
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