There is a vast literature on the throughput analysisof the IEEE 802.11 MAC protocol. However, very little has beendone on investigating the interplay between the collision avoidancemechanisms of the 802.11 MAC protocol and the dynamicsof upper-layer transport protocols. In this paper we tackle thisissue from an analytical, simulative and experimental perspective.Specifically, we develop Markov chain models to compute thedistribution of the number of active stations in an 802.11 WLANwhen long-lived TCP connections compete with finite load UDPflows.
By embedding these distributions in the MAC protocolmodelling, we derive approximate but accurate expressions ofthe TCP and UDP throughput. We validate the model accuracythrough performance tests carried out in a real WLAN for a widerange of configurations.
This paper presents an analytic model for evaluating the MAC layer queueing delays at wireless nodes using the distributed coordination function of IEEE 802.11 MAC specifications. In this paper, an improved analytical model for IEEE 802.11 distributed coordination function (DCF) under finite load is proposed by closely following the specifications given in IEEE 802.11 standard. The model is investigated in terms of channel throughput under perfect and slow Rayleigh fading channels.
Our analytical model and the supportingexperimental outcomes show that: i) the total TCP throughput isbasically independent of the number of open TCP connections,and the aggregate TCP traffic can be equivalently modelled astwo saturated flows; and ii) in the saturated regime n UDP flowsobtain about n-times the aggregate throughput achieved by theTCP flows, independently of the overall number of persistentTCP connections. Index Terms-802.11 MAC protocol, TCP,UDP, performance modelling, Markov chain.
. 204 Downloads. Abstract We provide analytical models for capacity evaluation of an infrastructure IEEE 802.11 based network carrying TCP controlled file downloads or full-duplex packet telephone calls.
In each case the analytical models utilize the attempt probabilities from a well known fixed-point based saturation analysis. For TCP controlled file downloads, following Bruno et al. (In Networking ’04, LNCS 2042, pp.␣626–637), we model the number of wireless stations (STAs) with ACKs as a Markov renewal process embedded at packet success instants. In our work, analysis of the evolution between the embedded instants is done by using saturation analysis to provide state dependent attempt probabilities. We show that in spite of its simplicity, our model works well, by comparing various simulated quantities, such as collision probability, with values predicted from our model. Next we consider N constant bit rate VoIP calls terminating at N STAs.
We model the number of STAs that have an up-link voice packet as a Markov renewal process embedded at so called channel slot boundaries. Analysis of the evolution over a channel slot is done using saturation analysis as before. We find that again the AP is the bottleneck, and the system can support (in the sense of a bound on the probability of delay exceeding a given value) a number of calls less than that at which the arrival rate into the AP exceeds the average service rate applied to the AP. Finally, we extend the analytical model for VoIP calls to determine the call capacity of an 802.11b WLAN in a situation where VoIP calls originate from two different types of coders. We consider N 1 calls originating from Type 1 codecs and N 2 calls originating from Type 2 codecs. For G711 and G729 voice coders, we show that the analytical model again provides accurate results in comparison with simulations.