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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.comnet.2006.07.011 Byline: Fabio Ricciato (a), Francesco Vacirca (a)(b), Philipp Svoboda (a)(c) Keywords: Traffic analysis; Passive monitoring; Bottleneck detection; 3G; UMTS Abstract: In this work we address the problem of inferring the presence of a capacity bottleneck from passive measurements in a 3G mobile network. The study is based on one month of packet traces collected in the UMTS core network of mobilkom austria AG & Co KG, the leading mobile telecommunications provider in Austria, EU. During the measurement period a bottleneck link in the UMTS core network was revealed and removed, therefore the traces enable the accurate analysis and comparison of the traffic behavior in the two network conditions: with and without a capacity bottleneck. Two approaches to bottleneck detection are investigated. The first one is based on the signal analysis of the marginal rate distribution of the traffic aggregate along one day cycle. Since TCP-controlled traffic dominates the overall traffic mix, the presence of a bottleneck strains the aggregate rate distribution and compresses it against the capacity limit during the peak hour. The second approach is based on the analysis of several TCP performance parameters, e.g. estimated frequency of retransmissions. Such statistics are unstable due to the presence of few top users, but this effect can be counteracted with simple filtering methods. Both approaches are validated via simulations. Our results show that both approaches can be used to provide early warning about future occurrences of capacity bottlenecks, and can complement other existing monitoring tools in the operation of a production network. Author Affiliation: (a) ftw. Forschungszentrum Telekommunikation Wien, Donau-City-Strasse 1, A-1220 Vienna, Austria (b) Infocom Department, University of Roma, "La Sapienza", Via Eudossiana 18, 00184 Roma, Italy (c) INTHFT Department, Vienna University of Technology, Karlsplatz 13, A-1040 Wien, Austria Article History: Received 27 September 2005; Revised 23 June 2006; Accepted 12 July 2006 Article Note: (miscellaneous) Responsible Editor: X.S. Shen

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.comnet.2005.11.003 Byline: Francesco Vacirca (a)(b), Thomas Ziegler (a), Eduard Hasenleithner (a) Keywords: TCP; Spurious timeout; UMTS; GPRS Abstract: This paper proposes an algorithm to identify TCP spurious retransmission timeouts by post processing of packet traces monitored in operational networks. The operational principles of the algorithm and the assumptions behind its design are explained in detail as well as the situations in which the algorithm is prone to inaccuracies. By extensive measurements in a lab testbed using realistic round trip time characteristics as observed in operational wireless networks and FTP-like as well as Web-like traffic generators, it is shown that the algorithm is accurate in detection of spurious retransmission timeouts. Subsequently, the algorithm is applied to real traffic traces captured at several interfaces of an operational UMTS and GPRS network to analyze the frequency of spurious retransmission timeouts as well as the spurious timeout probability dependent on the load situation in the network and the flow size. This investigation, to our best knowledge the first on large scale TCP traffic traces monitored in an operational UMTS network, shows that spurious timeouts are infrequent events in the considered UMTS as well as the GPRS network. Among other findings, it is additionally shown that the ratio between spurious timeouts and other congestion recovery events experienced by TCP flows is low, indicating a negligible impact of spurious timeouts on TCP performance. Author Affiliation: (a) ftw. Forschungszentrum Telekommunikation Wien, Donau-City-Strasse 1, A-1220 Vienna, Austria (b) Infocom Department, University of Roma "La Sapienza", Via Eudossiana 18, 00184 Roma, Italy Article History: Received 30 July 2005; Revised 17 November 2005; Accepted 21 November 2005 Article Note: (miscellaneous) Responsible Editor: S. Palazzo