945 research outputs found
Joint buffer management and scheduling for input queued switches
Input queued (IQ) switches are highly scalable and they have been the focus of many studies from academia and industry. Many scheduling algorithms have been proposed for IQ switches. However, they do not consider the buffer space requirement inside an IQ switch that may render the scheduling algorithms inefficient in practical applications.
In this dissertation, the Queue Length Proportional (QLP) algorithm is proposed for IQ switches. QLP considers both the buffer management and the scheduling mechanism to obtain the optimal allocation region for both bandwidth and buffer space according to real traffic load. In addition, this dissertation introduces the Queue Proportional Fairness (QPF) criterion, which employs the cell loss ratio as the fairness metric. The research in this dissertation will show that the utilization of network resources will be improved significantly with QPF. Furthermore, to support diverse Quality of Service (QoS) requirements of heterogeneous and bursty traffic, the Weighted Minmax algorithm (WMinmax) is proposed to efficiently and dynamically allocate network resources.
Lastly, to support traffic with multiple priorities and also to handle the decouple problem in practice, this dissertation introduces the multiple dimension scheduling algorithm which aims to find the optimal scheduling region in the multiple Euclidean space
Equilibrium bandwidth and buffer allocations for elastic traffics
Consider a set of users sharing a network node under an allocation scheme that provides each user with a fixed minimum and a random extra amount of bandwidth and buffer. Allocations and prices are adjusted to adapt to resource availability and user demands. Equilibrium is achieved when all users optimize their utility and demand equals supply for nonfree resources. We analyze two models of user behavior. We show that at equilibrium expected return on purchasing variable resources can be higher than that on fixed resources. Thus users must balance the marginal increase in utility due to higher return on variable resources and the marginal decrease in utility due to their variability. For the first user model we further show that at equilibrium where such tradeoff is optimized all users hold strictly positive amounts of variable bandwidth and buffer. For the second model we show that if both variable bandwidth and buffer are scarce then at equilibrium every user either holds both variable resources or none
SIMULATIVE ANALYSIS OF ROUTING AND LINK ALLOCATION STRATEGIES IN ATM NETWORKS
For Broadband Integrated Services Digital (B-ISDN) networks ATM is a promising technology,
because it supports a wide range of services with different bandwidth demands,
traffic characteristics and QoS requirements. This diversity of services makes traffic control
in these networks much more complicated than in existing circuit or packet switched
networks. Traffic control procedures include both actions necessary for setting up virtual
connections (VC), such as bandwidth assignment, call admission, routing and resource
allocation and congestion control measures necessary to maintain throughput in overload
situations.
This paper deals with routing and link allocation, and analyses the performance of
such algorithms in terms of call blocking probability, link capacity utilization and QoS
parameters. In our model the network carries out the following steps when a call is offered
to the network:
(1) Assign an appropriate bandwidth to an offered call (Bandwidth assignment)
(2) Find a transmission path between the source and destination with enough available
transmission capacity (Routing)
(3) Allocate resource along that path (Link allocation)
We consider an example 5-node network [7], conduct an extensive survey of routing,
and link allocation algorithms. Regarding step (1) we employ the equivalent link capacity
assignment presented by various interesting papers [1]-[5]. We find that the choice of routing
and link allocation algorithms has a great impact on network performance, and that
different routing algorithms perform best under different network load values. Shortest
path routing (SPR) is a good candidate for low, alternate routing (AR) for medium and
non-alternate routing (NAR) for high traffic load values.
Concerning link allocation strategies, we find that partial overlap (POL) strategies
that seem to be able to present near optimal performance are superior to complete sharing
(CS) and complete partitioning (CP) strategies. As a further improvement of the POL
scheme, we propose a 2-level link allocation algorithm, which yields highest link utilization.
In this scheme, not only the accesses of different service classes to different virtual
paths (VPs) are controlled, but also an individual VP's transmission capacity is optimally
allocated to the service classes according to their bandwidth requirements in order to
assure high link utilization. This method seems to be adjustable to the fine degree of
granularity of bandwidth demands in B-ISDN networks.
It is shown that in order to minimize cell loss the call level resource allocation
plays a significant role: networks with the same buffer size switches display different cell
loss probabilities in the nodes and impose different end-to-end delay on cells if the link
allocation and routing differ. Again, we find that when traffic is tolerable by the network,
SPR causes the least cell loss. This can be explained by the fact that SPR spreads the
incoming calls in the network. It eagerly seeks new routes instead of utilizing the already
used but still not congested routes. SPR obviously wastes more rapidly link and buffer
capacity as traffic load becomes higher than the AR, which chooses a new route only
when it has to, i.e. when the route of higher priority becomes congested. That is why
we experience that as soon as the SPR starts loosing cells, it indicates that available
resources have been consumed and it rapidly goes up to very high blocking probabilities
after a small further increase of load
Quality of service optimization of multimedia traffic in mobile networks
Mobile communication systems have continued to evolve beyond the currently deployed Third
Generation (3G) systems with the main goal of providing higher capacity. Systems beyond 3G
are expected to cater for a wide variety of services such as speech, data, image transmission,
video, as well as multimedia services consisting of a combination of these. With the air interface
being the bottleneck in mobile networks, recent enhancing technologies such as the High Speed
Downlink Packet Access (HSDPA), incorporate major changes to the radio access segment of
3G Universal Mobile Telecommunications System (UMTS). HSDPA introduces new features
such as fast link adaptation mechanisms, fast packet scheduling, and physical layer retransmissions
in the base stations, necessitating buffering of data at the air interface which presents a
bottleneck to end-to-end communication. Hence, in order to provide end-to-end Quality of
Service (QoS) guarantees to multimedia services in wireless networks such as HSDPA, efficient
buffer management schemes are required at the air interface.
The main objective of this thesis is to propose and evaluate solutions that will address the
QoS optimization of multimedia traffic at the radio link interface of HSDPA systems. In the
thesis, a novel queuing system known as the Time-Space Priority (TSP) scheme is proposed for
multimedia traffic QoS control. TSP provides customized preferential treatment to the constituent
flows in the multimedia traffic to suit their diverse QoS requirements. With TSP queuing, the
real-time component of the multimedia traffic, being delay sensitive and loss tolerant, is given
transmission priority; while the non-real-time component, being loss sensitive and delay tolerant,
enjoys space priority. Hence, based on the TSP queuing paradigm, new buffer managementalgorithms are designed for joint QoS control of the diverse components in a multimedia session
of the same HSDPA user. In the thesis, a TSP based buffer management algorithm known as the
Enhanced Time Space Priority (E-TSP) is proposed for HSDPA. E-TSP incorporates flow
control mechanisms to mitigate congestion in the air interface buffer of a user with multimedia
session comprising real-time and non-real-time flows. Thus, E-TSP is designed to provide
efficient network and radio resource utilization to improve end-to-end multimedia traffic
performance. In order to allow real-time optimization of the QoS control between the real-time
and non-real-time flows of the HSDPA multimedia session, another TSP based buffer management
algorithm known as the Dynamic Time Space Priority (D-TSP) is proposed. D-TSP
incorporates dynamic priority switching between the real-time and non-real-time flows. D-TSP
is designed to allow optimum QoS trade-off between the flows whilst still guaranteeing the
stringent real-time componentâs QoS requirements. The thesis presents results of extensive
performance studies undertaken via analytical modelling and dynamic network-level HSDPA
simulations demonstrating the effectiveness of the proposed TSP queuing system and the TSP
based buffer management schemes
Performance analysis of virtual path over large-scale ATM switches.
by Tang Oo.Thesis submitted in: December 1997.Thesis (M.Phil.)--Chinese University of Hong Kong, 1998.Includes bibliographical references (leaves 68-[75]).Abstract also in Chinese.Chapter 1 --- Introduction --- p.1Chapter 1.1 --- Background --- p.1Chapter 1.2 --- The Concept of Cross-Path Switching --- p.8Chapter 1.3 --- Contribution and Organization of Thesis --- p.12Chapter 2 --- The Virtual Path Scheduling Scheme --- p.14Chapter 2.1 --- The Trade-off Between Throughput and Concentration Loss --- p.14Chapter 2.2 --- Partition of Virtual Paths --- p.19Chapter 2.3 --- The Capacity and Route Assignment of Virtual Paths --- p.21Chapter 3 --- Performance Analysis and Simulation Results --- p.28Chapter 3.1 --- The Improvement of Concentration Loss --- p.28Chapter 3.2 --- The Throughput with Look-ahead Scheme --- p.30Chapter 3.3 --- The Throughput with Input Smoothing Scheme --- p.34Chapter 3.4 --- The Throughput with Bursty Source --- p.37Chapter 3.5 --- Buffer Dimensioning and The Cell Loss Probability Due to Buffer Overflow --- p.38Chapter 4 --- Capacity Assignment and Evaluation of Multiplexing Gain --- p.47Chapter 4.1 --- Principle of Capacity Assignment --- p.47Chapter 4.2 --- The Model of Virtual Path --- p.49Chapter 4.3 --- Capacity Assignment for CBR Service --- p.51Chapter 4.4 --- Capacity Assignment for Real-time VBR Service --- p.53Chapter 4.5 --- Capacity Assignment for Non Real-time VBR Service --- p.55Chapter 4.6 --- Capacity Matrix --- p.56Chapter 4.7 --- The Evaluation of Multiplexing Gain of Input Stage --- p.58Chapter 5 --- Discussions and Conclusions --- p.64Bibliography --- p.6
Dynamic bandwidth allocation in multi-class IP networks using utility functions.
PhDAbstact not availableFujitsu Telecommunications Europe Lt
Marginal Productivity Indices and Linear Programming Relaxations for Dynamic Resource Allocation in Queueing Systems
Many problems concerning resource management in modern communication systems can be simplified to queueing models under Markovian assumptions. The computation of the optimal policy is however often hindered by the curse of dimensionality especially for models that support multiple traffic or job classes. The research focus naturally turns to computationally efficient bounds and high performance heuristics. In this thesis, we apply the indexability theory to the study of admission control of a single server queue and to the buffer sharing problem for a multi-class queueing system. Our main contributions are the following: we derive the Marginal Productivity Index (MPI) and give a sufficient indexability condition for the admission control model by viewing the buffer as the resource; we construct hierarchical Linear Programming (LP) relaxations for the buffer sharing problem and propose an MPI based heuristic with its performance evaluated by discrete event simulation. In our study, the admission control model is used as the building block for the MPI heuristic deployed for the buffer sharing problem. Our condition for indexability only requires that the reward function is concavelike. We also give the explicit non-recursive expression for the MPI calculation. We compare with the previous result of the indexability condition and the MPI for the admission control model that penalizes the rejection action. The study of hierarchical LP relaxations for the buffer sharing problem is based on the exact but intractable LP formulation of the continuous-time Markov Decision Process (MDP). The number of hierarchy levels is equal to the number of job classes. The last one in the hierarchy is exact and corresponds to the exponentially sized LP formulation of the MDP. The first order relaxation is obtained by relaxing the constraint that no buffer overflow may occur in any sample path to the constraint that the average buffer utilization does not exceed the available capacity. Based on the Lagrangian decomposition of the first order relaxation, we propose a heuristic policy based on the concept of MPI. Each one of the decomposed subproblems corresponds to the admission control model we described above. The link to the decomposed sub-problems is the Lagrangian multiplier for the relaxed buffer size constraint in the first order relaxation. Our simulation study indicates the near optimal performance of the heuristic in the (randomly generated) instances investigated
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