Window size and round-trip-time in a network transmission session

A transmission session in a network constitutes a period beginning with the transport of data from one communicating node to the other. A transmission session is always set out for end-to-end connection and involves many network resources. Previous research studies on smooth data flow across a network reveals that the maximum number of data in an optimal transmission session is associated with window size. Problems are still encountered when it comes to the rate at which data move in a transmission session and also the required window size. This should be dynamically and automatically controlled. This research investigates the effect of Window Size and Round-Trip Time (RTT) in a transmission session. Packet data are collected for many network transmission sessions. The raw data were normalized, and the Naïve Bayes technique was used for the analytical evaluation. The effect of window size and RTT in a transmission session is examined, which reveals that the rate at which data move in a transmission session can be dynamically controlled to a considerably high degree of accuracy. Each network node cannot be overwhelmed when the window size is adjusted to the required siz

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

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 a 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, 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 in a commercial CDMA2000 network and its 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, we empirically demonstrate the impact of the wireless scheduler on various TCP parameters such as the round trip time, throughput and packet loss rate

Inferring congestion from delay and loss characteristics using parameters of the three-parameter Weibull distribution

Please read the abstract in the section “front” of this documentDissertation (MSc (Applied Science))--University of Pretoria, 2007.Electrical, Electronic and Computer EngineeringMScunrestricte

Is the Round-trip Time Correlated with the Number of Packets in Flight?

TCP uses packet loss as a feedback from the network to adapt its sending rate. TCP keeps increasing its sending rate as long as no packet loss occurs (unless constrained by bu#er size). Alternative congestion avoidance techniques (CATs) have been proposed to avoid such "aggressive" behavior. These CATs use simple statistics on observed roundtrip times and/or throughput of a TCP connection in response to variations in congestion window size. These CATs have a supposed ability to detect queue build-up

Is the Round-trip Time Correlated with the Number of Packets in Flight ?

TCP uses packet loss as a feedback from the network to adapt its sending rate. TCP keeps increasing its sending rate regardless of the network congestion state as long as no loss occurs (unless constrained by buffer size). Alternative congestion avoidance techniques (CATs) have been proposed to avoid such "agressive" behavior. These CATs use simple statistics on observed round-trip times and/or throughput of a TCP connection in response to variations in congestion window size. These CATs have a supposed ability to detect queue build-up. Such ability may be used to distinghish congestion losses from transmission losses. A previous study shows that these CATs do not yield interesting results for diagnosing the real reason of a loss

An Efficient Framework of Congestion Control for Next-Generation Networks

The success of the Internet can partly be attributed to the congestion control algorithm in the Transmission Control Protocol (TCP). However, with the tremendous increase in the diversity of networked systems and applications, TCP performance limitations are becoming increasingly problematic and the need for new transport protocol designs has become increasingly important.Prior research has focused on the design of either end-to-end protocols (e.g., CUBIC) that rely on implicit congestion signals such as loss and/or delay or network-based protocols (e.g., XCP) that use precise per-flow feedback from the network. While the former category of schemes haveperformance limitations, the latter are hard to deploy, can introduce high per-packet overhead, and open up new security challenges. This dissertation explores the middle ground between these designs and makes four contributions. First, we study the interplay between performance and feedback in congestion control protocols. We argue that congestion feedback in the form of aggregate load can provide the richness needed to meet the challenges of next-generation networks and applications. Second, we present the design, analysis, and evaluation of an efficient framework for congestion control called Binary Marking Congestion Control (BMCC). BMCC uses aggregate load feedback to achieve efficient and fair bandwidth allocations on high bandwidth-delaynetworks while minimizing packet loss rates and average queue length. BMCC reduces flow completiontimes by up to 4x over TCP and uses only the existing Explicit Congestion Notification bits.Next, we consider the incremental deployment of BMCC. We study the bandwidth sharing properties of BMCC and TCP over different partial deployment scenarios. We then present algorithms for ensuring safe co-existence of BMCC and TCP on the Internet. Finally, we consider the performance of BMCC over Wireless LANs. We show that the time-varying nature of the capacity of a WLAN can lead to significant performance issues for protocols that require capacity estimates for feedback computation. Using a simple model we characterize the capacity of a WLAN and propose the usage of the average service rate experienced by network layer packets as an estimate for capacity. Through extensive evaluation, we show that the resulting estimates provide good performance