195,193 research outputs found
TCP-Aware Backpressure Routing and Scheduling
In this work, we explore the performance of backpressure routing and
scheduling for TCP flows over wireless networks. TCP and backpressure are not
compatible due to a mismatch between the congestion control mechanism of TCP
and the queue size based routing and scheduling of the backpressure framework.
We propose a TCP-aware backpressure routing and scheduling that takes into
account the behavior of TCP flows. TCP-aware backpressure (i) provides
throughput optimality guarantees in the Lyapunov optimization framework, (ii)
gracefully combines TCP and backpressure without making any changes to the TCP
protocol, (iii) improves the throughput of TCP flows significantly, and (iv)
provides fairness across competing TCP flows
Modeling Network Coded TCP Throughput: A Simple Model and its Validation
We analyze the performance of TCP and TCP with network coding (TCP/NC) in
lossy wireless networks. We build upon the simple framework introduced by
Padhye et al. and characterize the throughput behavior of classical TCP as well
as TCP/NC as a function of erasure rate, round-trip time, maximum window size,
and duration of the connection. Our analytical results show that network coding
masks erasures and losses from TCP, thus preventing TCP's performance
degradation in lossy networks, such as wireless networks. It is further seen
that TCP/NC has significant throughput gains over TCP. In addition, we simulate
TCP and TCP/NC to verify our analysis of the average throughput and the window
evolution. Our analysis and simulation results show very close concordance and
support that TCP/NC is robust against erasures. TCP/NC is not only able to
increase its window size faster but also to maintain a large window size
despite losses within the network, whereas TCP experiences window closing
essentially because losses are mistakenly attributed to congestion.Comment: 9 pages, 12 figures, 1 table, submitted to IEEE INFOCOM 201
Throughput and fairness of multiple TCP connections in wireless networks
TCP suffers from poor throughput performance in wireless networks. Furthermore, when multiple TCP connections compete at the base station, link errors and congestion lead to serious unfairness among the connections. Although the issue of TCP performance in wireless networks has attracted significant attention, most reports focus only on TCP throughput and assume that there is only a single connection in a congestion-free network. This paper studies the throughput and fairness of popular improvement mechanisms (the Snoop [8] and ELN [5]) and TCP variants with multiple TCP connections. Simulation results show that the improvement mechanisms under investigation are effective to improve TCP throughput in a wireless network. However, they cannot provide fairness among multiple TCP connections. From the studies presented, it is concluded that mechanisms to enhance TCP fairness are needed in wireless network
The certainty principle
The notion of the quantum angle is introduced. The quantum angle turns out to
be a metric on the set of physical states of a quantum system. Its kinematics
and dynamics is studied. The certainty principle for quantum systems is
formulated and proved. It turns out that the certainty principle is closely
connected with the Heisenberg uncertainty principle (it presents, in some
sense, an opposite point of view). But at the same time the certainty principle
allows to give rigorous formulations for wider class of problems (it allows to
rigorously interpret and ground the analogous inequalities for the pairs of
quantities like time - energy, angle - angular momentum etc.)Comment: One paper, in Russian and in English, no figure
Analysis of Multiple Flows using Different High Speed TCP protocols on a General Network
We develop analytical tools for performance analysis of multiple TCP flows
(which could be using TCP CUBIC, TCP Compound, TCP New Reno) passing through a
multi-hop network. We first compute average window size for a single TCP
connection (using CUBIC or Compound TCP) under random losses. We then consider
two techniques to compute steady state throughput for different TCP flows in a
multi-hop network. In the first technique, we approximate the queues as M/G/1
queues. In the second technique, we use an optimization program whose solution
approximates the steady state throughput of the different flows. Our results
match well with ns2 simulations.Comment: Submitted to Performance Evaluatio
TCP smart framing: a segmentation algorithm to reduce TCP latency
TCP Smart Framing, or TCP-SF for short, enables the Fast Retransmit/Recovery algorithms even when the congestion window is small. Without modifying the TCP congestion control based on the additive-increase/multiplicative-decrease paradigm, TCP-SF adopts a novel segmentation algorithm: while Classic TCP always tries to send full-sized segments, a TCP-SF source adopts a more flexible segmentation algorithm to try and always have a number of in-flight segments larger than 3 so as to enable Fast Recovery. We motivate this choice by real traffic measurements, which indicate that today's traffic is populated by short-lived flows, whose only means to recover from a packet loss is by triggering a Retransmission Timeout. The key idea of TCP-SF can be implemented on top of any TCP flavor, from Tahoe to SACK, and requires modifications to the server TCP stack only, and can be easily coupled with recent TCP enhancements. The performance of the proposed TCP modification were studied by means of simulations, live measurements and an analytical model. In addition, the analytical model we have devised has a general scope, making it a valid tool for TCP performance evaluation in the small window region. Improvements are remarkable under several buffer management schemes, and maximized by byte-oriented schemes
DTMsim - DTM channel simulation in ns
Dynamic Transfer Mode (DTM) is a ring based MAN technology that
provides a channel abstraction with a dynamically adjustable capacity.
TCP is a reliable end to end transport protocol capable of adjusting
its rate. The primary goal of this work is investigate the coupling
of dynamically allocating bandwidth to TCP flows with the affect this
has on the congestion control mechanism of TCP. In particular we
wanted to find scenerios where this scheme does not work, where either
all the link capacity is allocated to TCP or congestion collapse
occurs and no capacity is allocated to TCP. We have created a
simulation environment using ns-2 to investigate TCP over networks
which have a variable capacity link. We begin with a single TCP Tahoe
flow over a fixed bandwidth link and progressively add more complexity
to understand the behaviour of dynamically adjusting link capacity to
TCP and vice versa
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