The widespread use of the IEEE 802.11 MAC as a layer-2 protocol for wireless local area networks has generated an extensive literature on its performance modelling. However, most of the available studies evaluate the capacity of WLANs in saturated conditions, while very little has been done on investigating the interactions between the 802.11 MAC protocol and the various transport protocols that are used to deliver users' traffic. In this paper we tackle this issue from both an analytical and experimental perspective. In particular, we first develop a Markov-based stochastic model to compute the number of active stations in an 802.11-based WLAN when persistent TCP connections compete with finite load UDP sources. This result is then used to derive approximate expressions for the TCP and UDP throughput by embedding the network backlog distribution in the MAC protocol modelling.A large set of experiments conducted in a real network validates the model accuracy for a wide range of configurations. A particular emphasis is devoted to investigate and explain the TCP and UDP fairness characteristics. Our analytical model and the supporting experimental outcomes demonstrate that: i) aggregated TCP throughput is basically independent of the total number of TCP stations; and ii) there is a fair allocation of channel bandwidth between TCP-controlled connections, while UDP flows rapidly take advantage over the TCP flows by increasing the UDP offered load.
Dr. Marco Conti is the Head of the Internet Networks department of Institute of Informatics and Telematics (IIT) of the Italian National Research Council (CNR). He is the co-chair of the Pervasive Computing and Networking laboratory (a joint laboratory of IIT-CNR and the department of Information Engineering at University of Pisa). He published in journals and conference proceedings more than 180 research papers related to design, modeling, and performance evaluation of computer-network architectures and protocols.
He co-authored the book "Metropolitan Area Networks" (Springer, London 1997) and is co-editor of the book "Mobile Ad Hoc Networking" (IEEE-Wiley 2004). He has been the coordinator of the project "Mobile Metropolitan Ad hoc Network (MobileMAN)" (2002-2005) funded by the European Commission in the framework of the FET-IST program. He served as TPC chair of several conferences including, IFIP-TC6 Networking 2002, IEEE WoWMoM 2005 and IEEE PerCom 2006, and ACM MobiHoc 2006. He is Associate Editor of the Pervasive and Mobile Computing journal (Elsevier), and Area Editor for IEEE Transactions on Mobile Computing, and Ad Hoc Networks Journal.
