• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.40 no.8
• /
• pp.1542-1550
• /
• 2015

Delayed ACK is an algorithm implemented to decrease the number of ACK transmissions by delaying an ACK transmission and by waiting for additional ACK instead of transmitting the ACK immediately. By using Delayed ACK in TCP, the congestion of network and the overhead of handling ACKs can be reduced. Waiting time of Delayed ACK is defined as the Delayed ACK timeout, and it is fixed in Window OS basically. However, the fixed value of Delayed ACK timeout is not suitable for dynamic network circumstance, and it may cause unnecessary delay. This paper proposes a regulating Delayed ACK timeout algorithm to reduce the aforementioned unnecessary delay caused by the lengthy default value of the Delayed ACK timeout. We confirm that TCP transmission performance in dynamic network circumstance can be improved using the proposed algorithm.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.32 no.2B
• /
• pp.124-132
• /
• 2007

Where a wireless LAN and a cellular network coexist, a mobile node has to experience vertical handoffs to move between them. Immediately after the vertical handoffs, TCP must need adaptation latency to adjust its congestion window to the proper size at a newly arrived network to use full of a new end-to-end available bandwidth. Even though SACK TCP has the best performance among other regular TCPs in the previous studies, it still cannot use full of the new available bandwidth quickly due to its inefficient increasing way of congestion window. BIC TCP, that becomes a popular TCP in long fat networks, has great feature working well against vertical handoffs by increasing congestion window exponentially with TCP connection sustained. In this paper, we derive adaptation latency of SACK TCP and BIC TCP numerically, and verify them by simulations. We also find that the shorter adaptation latency of BIC TCP produces higher throughput than SACK TCP on vertical handoffs. Consequently, to get higher performance on vertical handoff situations, we propose to use BIC TCP.

• The KIPS Transactions:PartC
• /
• v.12C no.1 s.97
• /
• pp.121-128
• /
• 2005

Tho existing TCP(Transmission Control Protocol) is known to be unsuitable for a network with the characteristics of high RDP(Bandwidth-Delay Product) because of the fixed small or large buffer size at the TCP sender and receiver. Thus, some trial cases of adjusting the buffer sizes automatically with respect to network condition have been proposed to improve the end-to-end TCP throughput. ATBT(Automatic TCP fluffer Tuning) attempts to assure the buffer size of TCP sender according to its current congestion window size but the ATBT assumes that the buffer size of TCP receiver is maximum value that operating system defines. In DRS(Dynamic Right Sizing), by estimating the TCP arrival data of two times the amount TCP data received previously, the TCP receiver simply reserves the buffer size for the next arrival, accordingly. However, we do not need to reserve exactly two times of buffer size because of the possibility of TCP segment loss. We propose an efficient TCP buffer tuning technique(called TBT-PLR: TCP buffer tuning algorithm based on packet loss ratio) since we adopt the ATBT mechanism and the TBT-PLR mechanism for the TCP sender and the TCP receiver, respectively. For the purpose of testing the actual TCP performance, we implemented our TBT-PLR by modifying the linux kernel version 2.4.18 and evaluated the TCP performance by comparing TBT-PLR with the TCP schemes of the fixed buffer size. As a result, more balanced usage among TCP connections was obtained.