Keywords: slow start, congestion avoidance, TCP-Reno, duplicate ACK, analytical modeling
Received February 3, 2005; revised May 27 & August 23, 2005; accepted October 12, 2005.
Communicated by C. C. Jay Kuo.
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Tsang-Ling Sheu and Lien-Wen Wu
Department of Electrical Engineering
National Sun Yat-Sen University
Kaohsiung, 804 Taiwan
E-mail: sheu@ee.nsysu.edu.tw
This paper presents analytical modeling to systematically capture the characteristics
of TCP fast retransmission and recovery. One of the novel contributions of this paper is
to evaluate the conditions under which fast recovery can be successful in the slow start
and in the congestion avoidance phases, respectively. Unlike previous works where they
simply assume in a RTT round the packets following the first lost packet are all lost, we
consider a more realistic case in which the packets following the first lost packet in the
same RTT round may not be all lost. This consideration makes our analyses technically
different from the previous works as described in [1] and [4-6]. Depending on Nr[y], the
number of packets successfully received at the (y + 1)th RTT round after the first lost
packet was detected, we divide the analytical model into two cases: Nr[y] k (the number
of duplicate acknowledgments) and Nr[y] < k. For both cases, we have respectively
revealed that there are certain necessary conditions for the fast retransmission to occur.
The revealed necessary conditions are represented as a number of upper bounds, beyond
which the lost packets can not be recovered using TCP fast retransmission algorithm. In
addition, from the analytical results, we have shown that TCP Reno certainly leads to
timeout if the number of packet losses in a TCP window exceeds two packets.
Received February 3, 2005; revised May 27 & August 23, 2005; accepted October 12, 2005.
Communicated by C. C. Jay Kuo.