4 round trip times, in spite of the connection speed. HSTCP encourages packet losses at a slower speed than STCP, but still much quicker than RCP-Reno.
3. Problems of the Existing Delay-based TCP Versions
In contrast, TCP Vegas, Enhanced TCP Vegas and FAST TCP are delay-based protocols. By relying upon changes in queuing delay measurements to detect changes in available bandwidth, these delay-based protocols achieve higher average throughout with good intra-protocol RTT fairness (Cajon, 2004). However, they have more than a few deficiencies. For instance, both Vegas and FAST suffer from the overturn path congestion difficulty, in which simultaneous onward and overturn path traffic on a simple bidirectional blockage connection cannot attain full link operation. In addition, both Vegas and Enhanced Vegas employ a conservative window increase strategy of at most one packet ever RTT, leading to slow convergence to equilibrium when ample bandwidth is available. Although possessing an aggressive window increasing strategy leading to faster convergence in high-speed networks, we shall see that, FAST has trouble grappling with uncertainty in the networking infrastructure.
Similar to Vegas and Enhanced Vegas, FAST TCP attempts to buffer a fixed number, a, of packets in the router queues in the network loop path. In speedy networks, a must be adequately big to allow a delay-based protocol to calculate the line up delay. But with great values of a, the delay-based protocol inflicts supplementary buffering necessities on the network routers with an increase in the number of flows; the router queues may not be able to handle the demand. If the buffering supplies are not fulfilled, the delay-based protocols suffer failure, which mortifies their performance. In contrast, if ? is too diminutive, the queuing delay may not be detectable, and convergence to high throughput may be slow.
Preferably, in delay-based systems a source's worth of set-point ? must be animatedly attuned consistent with the connection capacities, queuing resources, and the number of simultaneous connections in common queues. To determine a sensible and effectual technique for enthusiastically setting a perhaps time-varying set-point ? (t) has remained as an open problem. Examples of delay-based schemes include TCP Vegas (1), Enhanced TCP Vegas and FAST TCP (C.Jin, 2004). While providing higher throughput that Reno, and exhibiting good intra-RTT fairness, the delay-based schemes still have shortcomings in terms of throughput and the selection of a suitable ?. In contrast to the marking / loss-based schemes, delay-based schemes primarily do not use marking/loss within their control strategies, often choosing to follow the tactics of TCP Reno when marking or loss is selected.
4. Analytical Approaches
In terms of characterizing and providing analytical accepting of TCP congestion evasion and control, several approaches based on stochastic modeling, control theory, game theory, and optimization theory have been presented. (S.Kunniyur, 2003)
In particular, Frank Kelly gave a general analytical framework based on distributed optimization theory. In terms of providing analytical guidance to TCP congestion avoidance methods utilizing delay-based feedback, Low (S.H.Low, 2002) urbanized a duality model of TCP Vegas, interpreting TCP congestion control as a distributed algorithm to solve a global optimization problem with the round-trip delays acting as pricing information. Throughout this structure, the resultant performance improvement of TCP Vegas and Fast TCP are better understood. Nonetheless, the expansion of extra analytical framework of TCP congestion avoidance is necessary.(S.Moscolo, 2006)
Network calculus (NC) offers a scientifically thorough approach to analyze network performance, permitting a system theoretic method of decomposing network demands into impulse responses and service curves by using the notion of convolution developed within the context of a certain min-plus algebra, Previously in (R.Agrawal, 1999), window flow control strategy based on an NC using a feedback instrument was urbanized, on condition that consequences concerning the impact on the window size and performance of the session. In terms to determine the most advantageous window size, the work by R.Agrawal (1999) merely recognizes that the window size ought to be reduced when the network is crowded, and augmented when extra resources are obtainable. In (C.S.Chang, 2002), the authors extend NC analysis to time-variant settings, providing a framework useful for window flow control. However, they do not develop an optimal controller. In (F.BAcclli, 2000), a (max, +) approach similar to NC-based techniques is utilized to describe the packet-level dynamics of the loss-based TCP Reno (S.Moscolo, 2006) and Tahoe, and calculate the TCP throughput. The work in...
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