Understanding Performance for Two 802.11 Competing Flows

Abstract

It is well known that 802.11 suffers from both inefficiency and unfairness in the face of competition and interference. This paper provides a detailed analysis of the impact of topology and traffic type on network performance when two flows compete with each other for airspace. We consider both TCP and UDP flows and a comprehensive set of node topologies. We vary these topologies to consider all combinations of the following four node-to-node interactions: (1) nodes unable to read or sense each other, (2) nodes able to sense each other but not able to read each other's packets and nodes able to communicate with (3) weak and with (4) strong signal. We evaluate all possible cases through simulation and show that the cases can be reduced to 9 UDP and 10 TCP 802.11g models with similar efficiency/fairness characteristics. We also validate our simulation results with extensive experiments conducted in a laboratory testbed. These more detailed models improve on previous work such as hidden-/exposed-terminal categorization and are thus better suited as a basis for adaptive techniques to improve performance in 802.11 multi-hop WLAN or Mesh Networks.

A Model for Congestion Control of Transmission Control Protocol in Mobile Wireless Ad Hoc Networks

“…We identified three factors that may contribute to increase the level of contention: (1) the large congestion window increases the contention among the TCP data packets in the forward path Chen et al, 2003;Kim et al, 2005;Triantafyllidou et al, 2009) (2) generating ACK for every arrived packet will increase the contention between data and ACK packets in the forward and return path (Singh and Kankipati, 2004;Oliveira and Braun, 2007;Chen et al, 2008) and (3) hidden and exposed terminals (Chen et al, 2008;Cai et al, 2008). These factors cause an excessive number of medium accesses (Cai et al, 2008;Kim et al, 2006) that increases the level of contention.…”

“…These factors cause an excessive number of medium accesses (Cai et al, 2008;Kim et al, 2006) that increases the level of contention. Consequently, the high level of contention may lead to one of the following: (1) degrade TCP performance; (2) increase the probability of route failure (Link E in Fig.…”

“…3 • Statement C-Large number of generated ACKs increases the level of contention (Singh and Kankipati, 2004;Oliveira and Braun, 2007;Chen et al, 2008), which is represented by Link C in Fig. 3 • Statement D-Hidden and exposed terminal increases the level of contention Cai et al, 2008), which is represented by Link D in Fig. 3 • Statement G-Large (high) contention level has negative impact on the TCP performance Chen et al, 2008) (i.e., poor throughput and fairness and high delay and packet loss), which is represented by Link G in Fig.…”

Trade: Cooperation without Trust in 802.11 Networks

“…In the figure a solid line between nodes indicates they can decode each other's messages and a dashed line indicates they cannot, but can still interfere with each other. If both access points attempt to transmit at 22 Mbps using the 802.11g maximum transmission rate of 54 Mbps, for example, the actual delivered throughput is 21 Mbps to one device and 1.5 Mbps to the other [5].…”