566 research outputs found
Adaptive Multicast of Multi-Layered Video: Rate-Based and Credit-Based Approaches
Network architectures that can efficiently transport high quality, multicast
video are rapidly becoming a basic requirement of emerging multimedia
applications. The main problem complicating multicast video transport is
variation in network bandwidth constraints. An attractive solution to this
problem is to use an adaptive, multi-layered video encoding mechanism. In this
paper, we consider two such mechanisms for the support of video multicast; one
is a rate-based mechanism that relies on explicit rate congestion feedback from
the network, and the other is a credit-based mechanism that relies on
hop-by-hop congestion feedback. The responsiveness, bandwidth utilization,
scalability and fairness of the two mechanisms are evaluated through
simulations. Results suggest that while the two mechanisms exhibit performance
trade-offs, both are capable of providing a high quality video service in the
presence of varying bandwidth constraints.Comment: 11 page
Optimization flow control -- I: Basic algorithm and convergence
We propose an optimization approach to flow control where the objective is to maximize the aggregate source utility over their transmission rates. We view network links and sources as processors of a distributed computation system to solve the dual problem using a gradient projection algorithm. In this system, sources select transmission rates that maximize their own benefits, utility minus bandwidth cost, and network links adjust bandwidth prices to coordinate the sources' decisions. We allow feedback delays to be different, substantial, and time varying, and links and sources to update at different times and with different frequencies. We provide asynchronous distributed algorithms and prove their convergence in a static environment. We present measurements obtained from a preliminary prototype to illustrate the convergence of the algorithm in a slowly time-varying environment. We discuss its fairness property
Energy-efficient wireless communication
In this chapter we present an energy-efficient highly adaptive network interface architecture and a novel data link layer protocol for wireless networks that provides Quality of Service (QoS) support for diverse traffic types. Due to the dynamic nature of wireless networks, adaptations in bandwidth scheduling and error control are necessary to achieve energy efficiency and an acceptable quality of service. In our approach we apply adaptability through all layers of the protocol stack, and provide feedback to the applications. In this way the applications can adapt the data streams, and the network protocols can adapt the communication parameters
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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