Investigation of the TCP simultaneous-send problem in 802.11 wireless local area networks

This paper investigates the TCP simultaneous-send problem (SSP) which arises in infrastructure mode WLANs. In particular it has been observed that for file transfer traffic, 802.11 wireless nodes have a sustained supply of packets to send and hence experience a relatively high rate of MAC contention. For TCP, this results in competition among data and ACK packets for channel access which causes the SSP that deteriorates flow throughput. This SSP can be alleviated by skipping TCP ACKs. Detailed simulation results are presented to demonstrate the usefulness of ACK skipping in various network scenarios such as with MAC retries and multiple TCP flows. The largest improvement is seen for the case of a single TCP flow, and moderate gains are also achieved in cases with multiple streams. For the single TCP stream case with 1 ACK skip and no MAC retries, TCP throughput improves 30% for short-lived and 98% for long-lived TCP transmissions. The paper concludes with potential cross-layer solutions that potentially provide further improvements, including the use of the point coordination function (PCF) to reduce contention between multiple TCP streams and returning ACK packets.

[1]  Vaduvur Bharghavan,et al.  WTCP: A Reliable Transport Protocol for Wireless Wide-Area Networks , 1999, Wirel. Networks.

[2]  Rajeev Shorey,et al.  Performance improvement of TCP with delayed ACKs in IEEE 802.11 wireless LANs , 2004, 2004 IEEE Wireless Communications and Networking Conference (IEEE Cat. No.04TH8733).

[3]  Haitao Wu,et al.  Performance of reliable transport protocol over IEEE 802.11 wireless LAN: analysis and enhancement , 2002, Proceedings.Twenty-First Annual Joint Conference of the IEEE Computer and Communications Societies.

[4]  K. Kanth,et al.  Performance enhancement of TCP on multihop ad hoc wireless networks , 2002, 2002 IEEE International Conference on Personal Wireless Communications.

[5]  Eitan Altman,et al.  Novel Delayed ACK Techniques for Improving TCP Performance in Multihop Wireless Networks , 2003, PWC.

[6]  Prasun Sinha,et al.  Understanding TCP fairness over wireless LAN , 2003, IEEE INFOCOM 2003. Twenty-second Annual Joint Conference of the IEEE Computer and Communications Societies (IEEE Cat. No.03CH37428).

[7]  Shugong Xu,et al.  Revealing and solving the TCP instability problem in 802.11 based multi-hop mobile ad hoc networks , 2001, IEEE 54th Vehicular Technology Conference. VTC Fall 2001. Proceedings (Cat. No.01CH37211).

[8]  Torsten Braun,et al.  TCP in Wireless Mobile Ad Hoc Networks , 2002 .

[9]  Chinya V. Ravishankar,et al.  Interactions between TCP and the IEEE 802.11 MAC protocol , 2003, Proceedings DARPA Information Survivability Conference and Exposition.

[10]  Guido Aben,et al.  Net throughput with IEEE 802.11 wireless LANs , 2000, 2000 IEEE Wireless Communications and Networking Conference. Conference Record (Cat. No.00TH8540).

[11]  L. Sanchez,et al.  An experimental study of Snoop TCP performance over the IEEE 802.11b WLAN , 2002, The 5th International Symposium on Wireless Personal Multimedia Communications.

[12]  Qixiang Pang,et al.  Performance study of TCP Veno over WLAN and RED router , 2003, GLOBECOM '03. IEEE Global Telecommunications Conference (IEEE Cat. No.03CH37489).

[13]  Shugong Xu,et al.  On TCP over wireless multi-hop networks , 2001, 2001 MILCOM Proceedings Communications for Network-Centric Operations: Creating the Information Force (Cat. No.01CH37277).

[14]  Klara Nahrstedt,et al.  On setting TCP's congestion window limit in mobile ad hoc networks , 2003, IEEE International Conference on Communications, 2003. ICC '03..