Transmission control protocol Westwood (TCPW) has been shown to provide significant performance improvement over high-speed heterogeneous networks. The key idea of TCPW is to use eligible rate estimation (ERE) methods to intelligently set the congestion window (cwnd) and slow-start threshold (ssthresh) after a packet loss. ERE is defined as the efficient transmission rate eligible for a sender to achieve high utilization and be friendly to other TCP variants. This work presents TCP Westwood with agile probing (TCPW-A), a sender-side only enhancement of TCPW, that deals well with highly dynamic bandwidth, large propagation time/bandwidth, and random loss in the current and future heterogeneous Internet. TCPW-A achieves this goal by adding the following two mechanisms to TCPW. 1) When a connection initially begins or restarts after a timeout, instead of exponentially expanding cwnd to an arbitrary preset sthresh and then going into linear increase, TCPW-A uses agile probing, a mechanism that repeatedly resets ssthresh based on ERE and forces cwnd into an exponential climb each time. The result is fast convergence to a more appropriate ssthresh value. 2) In congestion avoidance, TCPW-A invokes agile probing upon detection of persistent extra bandwidth via a scheme we call persistent noncongestion detection (PNCD). While in congestion avoidance, agile probing is actually invoked under the following conditions: a) a large amount of bandwidth that suddenly becomes available due to change in network conditions; b) random loss during slow-start that causes the connection to prematurely exit the slow-start phase. Experimental results, both in ns-2 simulation and lab measurements using actual protocols implementation, show that TCPW-A can significantly improve link utilization over a wide range of bandwidth, propagation delay, and dynamic network loading.

TCP westwood (TCPW) has been shown to provide significant performance improvement over high-speed heterogeneous networks. The key idea of TCPW is to use eligible rate estimation (ERE) methods, to set the congestion window (cwnd) and slow start threshold (ssthresh) after a packet loss. ERE is defined as the transmission rate a sender ought to use to achieve high utilization and remain friendly to other TCP variants. This paper presents TCP westwood with agile probing (TCPW-A), a sender-side only enhancement of TCPW. TCPW-A perform well when faced with highly dynamic bandwidth, large propagation time/bandwidth, and random loss in the current and future heterogeneous Internet. TCPW-A achieves its goal by incorporating the following, two mechanisms: 1) when a connection initially begins or re-starts after a timeout, instead of exponentially expanding cwnd to an arbitrary preset ssthresh and then going into linear increase. TCPW-A uses agile probing, a mechanism that repeatedly resets ssthresh based on ERE and forces cwnd into an exponential climb each time. The result is fast convergence to a more appropriate ssthresh value. 2) In congestion avoidance, TCPW-A invokes agile probing upon indication of unused extra bandwidth via a scheme we call load gauge (LG). Experimental results, both in Ns-2, and in measurements using FreeBSD implementation, show that TCPW-A can significantly improve link utilization over a wide range of bandwidth, propagation delay and dynamic network loading.

.4brtroct- Nest generation nehvorlis with large bandwidth and long drlay pose a major challenge to TCP performance, especially during the startup period. In this paper we evaluate the performance of TCP RenaiNcwrcno. Vegns and Hoe's modification in large bandwidth delay nrhvork. We propose n modified Slow-start mechanism, rnllcd Adaptive Start (Astart), to improve the startup performance in such networks. When a connection initially begins or re-starts after a coarse timrout,- Astart ndaptivcly and repentedly resets the Slow-start Threshold (suthreslr) based on an cligihlr sending I'iitr estimation mrchanisrn proposrd in TCP Westwond. By iidapting to network conditions during the startup phase. it wndw is able to grow the congestion window (ocnh fast without incurring risk of huNw owrflow and multiple Iossrs. Simulation rxpcrirncnts show that Astart can significantly improve the link utiliiation under various bandwidth, buNrr sur;~nd round-trip propagation timrs. The mrthud avoids both under-utiliriition dur to prrmature Slowstart termination, as wcll ils multiple I~XII~S due to initinlly setting srrlire.sli too high, or. increaing nmd tin) fiat. Experiments also show that Astart uchiews good fttirnrss rind fricndlincss toward TCP NewReno. Lab measuremrnts using a FrreBSD Astart implementation are also reported in this paper, providing futrhcr evidence of the gains nchirvahlr via Astart. Kqw-orr%r-congesrionn control;.sIow-.start; rate estimution. large bundwidth ddq nehvorks I.