On the Interaction between TCP and the Wireless Channel in CDMA2000 Networks

In this work, we conducted extensive active measurements on a large nationwide CDMA2000 1xRTT network in order to characterize the impact of both the Radio Link Protocol and more importantly, the wireless scheduler, on TCP. Our measurements include standard TCP/UDP logs, as well as detailed RF layer statistics that allow observability into RF dynamics. With the help of a robust correlation measure, normalized mutual information, we were able to quantify the impact of these two RF factors on TCP performance metrics such as the round trip time, packet loss rate, instantaneous throughput etc. We show that the variable channel rate has the larger impact on TCP behavior when compared to the Radio Link Protocol. Furthermore, we expose and rank the factors that influence the assigned channel rate itself and in particular, demonstrate the sensitivity of the wireless scheduler to the data sending rate. Thus, TCP is adapting its rate to match the available network capacity, while the rate allocated by the wireless scheduler is influenced by the sender's behavior. Such a system is best described as a closed loop system with two feedback controllers, the TCP controller and the wireless scheduler, each one affecting the other's decisions. In this work, we take the first steps in characterizing such a system in a realistic environment

TCP over CDMA2000 Networks: A Cross-Layer Measurement Study

Modern cellular channels in 3G networks incorporate sophisticated power control and dynamic rate adaptation which can have significant impact on adaptive transport layer protocols, such as TCP. Though there exists studies that have evaluated the performance of TCP over such networks, they are based solely on observations at the transport layer and hence have no visibility into the impact of lower layer dynamics, which are a key characteristic of these networks. In this work, we present a detailed characterization of TCP behavior based on cross-layer measurement of transport layer, as well as RF and MAC layer parameters. In particular, through a series of active TCP/UDP experiments and measurement of the relevant variables at all three layers, we characterize both, the wireless scheduler and the radio link protocol in a commercial CDMA2000 network and assess their impact on TCP dynamics. Somewhat surprisingly, our findings indicate that the wireless scheduler is mostly insensitive to channel quality and sector load over short timescales and is mainly affected by the transport layer data rate. Furthermore, with the help of a robust correlation measure, Normalized Mutual Information, we were able to quantify the impact of the wireless scheduler and the radio link protocol on various TCP parameters such as the round trip time, throughput and packet loss rate

Epidemiologic study of myelodysplastic syndromes in a multiethnic, inner city cohort

Little is known about the epidemiology of MDS in minority populations. The IPSS and newly released IPSS-R are important clinical tools in prognostication of patients with MDS. Therefore, we conducted a retrospective epidemiological analysis of MDS in an ethnically diverse cohort of patients. Demographics, disease characteristics, and survival were determined in 161 patients seen at Montefiore Medical Center from 1997 to 2011. We observed that Hispanics presented at a younger age than blacks and whites (68 vs. 73.7 vs. 75.6 years); this difference was significant (p = 0.01). A trend towards greater prevalence of thrombocytopenia in Hispanics was observed, but this was not significant (p = 0.08). No other differences between the groups were observed. Overall median survival after diagnosis was the highest among Hispanics (8.6 years) followed by blacks (6.2 years) and Caucasians (3.7). Adjusted hazard ratios however did not show significant differences in risk of death between the groups. The IPSS-R showed slightly better discrimination when compared to the IPSS in this cohort (Somers Dxy 0.39 vs. 0.35, respectively) but observed survival more was more closely approximated by IPSS than by IPSS-R. Our study highlights the possibility of ethnic differences in the presentation of MDS and raises questions regarding which prognostic system is more predictive in this population

Impact of traffic and network information on routing performance

Traffic engineering is aimed at distribution of traffic within a network so as to optimize a given performance criterion. It typically takes as input, a certain characterization of the traffic, network topology and routing constraints, and outputs a set of paths that optimize a specified objective. The ability to carry out such an optimal distribution depends on the routing and forwarding mechanisms, the traffic information available, the network characteristics and finally, the route computation algorithm. The goal of this thesis is to explore the interplay between these factors and their impact on performance, both in terms of cost and robustness, as well as the associated complexity. We approach this objective from the perspective of analyzing the impact of information in a problem. In particular, the volume of traffic and network information along with the routing constraints play a vital role in determining the complexity of computing and implementing a good routing solution as well as its performance. The focus of our investigation is on identifying what type and amount of information in the input is relevant and how they affect the trade-off between improvement in performance and the increase in complexity associated with the use of a larger volume of information. In order to aid our study, several algorithms are derived that are shown, through analysis and experimental evidence, to efficiently exploit input information and still yield good performance. An important aspect of our investigation is that we explore these issues under realistic constraints imposed by both MPLS type environments as well as shortest path protocols like OSPF and IS-IS, which govern the paths that are allowed within a network as well as the distribution of traffic over these paths. These constraints are utilized to identify the relevant information present in the traffic matrix and the network. With regard to traffic matrices, we study the impact of information present in the form of traffic granularity. In practice, the traffic matrix is granular in nature, with traffic distributed over a set of discrete entities or streams, which constitute our measure of information. The distribution of traffic in the network is governed by the routing and forwarding decisions made for each such stream. Present day forwarding mechanisms constrain traffic on each stream to be split in a very limited number of ways. (Abstract shortened by UMI.

Impact of traffic and network information on routing performance

Traffic engineering is aimed at distribution of traffic within a network so as to optimize a given performance criterion. It typically takes as input, a certain characterization of the traffic, network topology and routing constraints, and outputs a set of paths that optimize a specified objective. The ability to carry out such an optimal distribution depends on the routing and forwarding mechanisms, the traffic information available, the network characteristics and finally, the route computation algorithm. The goal of this thesis is to explore the interplay between these factors and their impact on performance, both in terms of cost and robustness, as well as the associated complexity. We approach this objective from the perspective of analyzing the impact of information in a problem. In particular, the volume of traffic and network information along with the routing constraints play a vital role in determining the complexity of computing and implementing a good routing solution as well as its performance. The focus of our investigation is on identifying what type and amount of information in the input is relevant and how they affect the trade-off between improvement in performance and the increase in complexity associated with the use of a larger volume of information. In order to aid our study, several algorithms are derived that are shown, through analysis and experimental evidence, to efficiently exploit input information and still yield good performance. An important aspect of our investigation is that we explore these issues under realistic constraints imposed by both MPLS type environments as well as shortest path protocols like OSPF and IS-IS, which govern the paths that are allowed within a network as well as the distribution of traffic over these paths. These constraints are utilized to identify the relevant information present in the traffic matrix and the network. With regard to traffic matrices, we study the impact of information present in the form of traffic granularity. In practice, the traffic matrix is granular in nature, with traffic distributed over a set of discrete entities or streams, which constitute our measure of information. The distribution of traffic in the network is governed by the routing and forwarding decisions made for each such stream. Present day forwarding mechanisms constrain traffic on each stream to be split in a very limited number of ways. (Abstract shortened by UMI.

Making IGP Routing Robust to Link Failures

Abstract. An important requirement of a robust traffic engineering solution is insensitivity to changes, be they in the form of traffic fluctuations or changes in the network topology because of link failures. In this paper we focus on developing a fast and effective technique to compute traffic engineering solutions for Interior Gateway Protocol (IGPs) environments that are robust to link failures in the logical topology. The routing and packet forwarding decisions for IGPs is primarily governed by link weights. Our focus is on computing a single set of link weights for a traffic engineering instance that performs well over all single logical link failures. Such types of failures, although usually not long lasting, of the order of tens of minutes, can occur with high enough frequency, of the order of several a day, to significantly affect network performance. The relatively short duration of such failures coupled with issues of computational complexity and convergence time due to the size of current day networks discourage adaptive reactions to such events. Consequently, it is desirable to aprioricompute a routing solution that performs well in all such scenarios. Through computational evaluations we demonstrate that our technique yields link weights that perform well over all single link failures and also scales well, in terms of computational complexity, with the size of the network

Making IGP Routing Robust to Link Failures

Abstract. An important requirement of a robust traffic engineering solution is insensitivity to changes, be they in the form of traffic fluctuations or changes in the network topology because of link failures. In this paper we focus on developing a fast and effective technique to compute traffic engineering solutions for Interior Gateway Protocol (IGPs) environments that are robust to link failures in the logical topology. The routing and packet forwarding decisions for IGPs is primarily governed by link weights. Our focus is on computing a single set of link weights for a traffic engineering instance that performs well over all single logical link failures. Such types of failures, although usually not long lasting, of the order of tens of minutes, can occur with high enough frequency, of the order of several a day, to significantly affect network performance. The relatively short duration of such failures coupled with issues of computational complexity and convergence time due to the size of current day networks discourage adaptive reactions to such events. Consequently, it is desirable to a priori compute a routing solution that performs well in all such scenarios. Through computational evaluations we demonstrate that our technique yields link weights that perform well over all single link failures and also scales well, in terms of computational complexity, with the size of the network