Refining TCP's RTT dependent mechanism by utilizing link retransmission delay measurement in Wireless LAN

Abstract

Network utilization by legacy transmission control protocol (TCP) is determined by its round trip time (RTT) dependent mechanism for the growth of its sending rate. The RTT does not always reflect the actual network conditions, especially in the case of wireless local area network (WLAN). Consequently, it influences the RTT-dependent mechanism falsely. This paper proposes a novel cross-layer scheme between TCP and the Institute of Electrical and Electronics Engineers (IEEE) 802.11 medium access control (MAC) that compensates for any diminished growth of TCP's sending rate because of the inclusion of non-congestion delay component in RTT, if any. The proposed scheme has two refinements. The first refinement is at the MAC layer that notifies the additional propagation delay on account of link retransmission of a TCP packet. The second refinement is at the TCP layer in which the sender adapts the sending rate by relating the aforementioned additional propagation delay to the RTT estimation. To examine the benefits, the proposed scheme is evaluated after implementing it on top of representative TCP variants; Newreno and Westwood+ (TCPW). Simulation results showed that with the proposed scheme, network utilization by native TCP is improved by more than 35% in a dedicated WLAN environment, while the performance remained protected in a shared WLAN environment.

Downlink and Uplink Message Size Impact on Round Trip Time Metric in Multi-Hop Wireless Mesh Networks

“…RTT is effective and profitable in measuring the congestion window size and retransmission timeout of a connection [1] [2] [3] as well as the available bandwidth on an along path [4]. This information can help fixed, determine factors that limit data flow rates and cause congestion [5].…”