92 research outputs found
An Adaptive Scheme for Admission Control in ATM Networks
This paper presents a real time front-end admission control scheme for ATM networks. A call management scheme which uses the burstiness associated with traffic sources in a heterogeneous ATM environment to effect dynamic assignment of bandwidth is presented. In the proposed scheme, call acceptance is based on an on-line evaluation of the upper bound on cell loss probability which is derived from the estimated distribution of the number of calls arriving. Using this scheme, the negotiated quality of service will be assured when there is no estimation error. The control mechanism is effective when the number of calls is large, and tolerates loose bandwidth enforcement and loose policing control. The proposed approach is very effective in the connection oriented transport of ATM networks where the decision to admit new traffic is based on thea priori knowledge of the state of the route taken by the traffic
Investigation of delay jitter of heterogeneous traffic in broadband networks
Scope and Methodology of Study: A critical challenge for both wired and wireless networking vendors and carrier companies is to be able to accurately estimate the quality of service (QoS) that will be provided based on the network architecture, router/switch topology, and protocol applied. As a result, this thesis focuses on the theoretical analysis of QoS parameters in term of inter-arrival jitter in differentiated services networks by deploying analytic/mathematical modeling technique and queueing theory, where the analytic model is expressed in terms of a set of equations that can be solved to yield the desired delay jitter parameter. In wireless networks with homogeneous traffic, the effects on the delay jitter in reference to the priority control scheme of the ARQ traffic for the two cases of: 1) the ARQ traffic has a priority over the original transmission traffic; and 2) the ARQ traffic has no priority over the original transmission traffic are evaluated. In wired broadband networks with heterogeneous traffic, the jitter analysis is conducted and the algorithm to control its effect is also developed.Findings and Conclusions: First, the results show that high priority packets always maintain the minimum inter-arrival jitter, which will not be affected even in heavy load situation. Second, the Gaussian traffic modeling is applied using the MVA approach to conduct the queue length analysis, and then the jitter analysis in heterogeneous broadband networks is investigated. While for wireless networks with homogeneous traffic, binomial distribution is used to conduct the queue length analysis, which is sufficient and relatively easy compared to heterogeneous traffic. Third, develop a service discipline called the tagged stream adaptive distortion-reducing peak output-rate enforcing to control and avoid the delay jitter increases without bound in heterogeneous broadband networks. Finally, through the analysis provided, the differential services, was proved not only viable, but also effective to control delay jitter. The analytic models that serve as guidelines to assist network system designers in controlling the QoS requested by customer in term of delay jitter
Trunk Sizing in Packet Networks- the Effect on User Quality of Service
Electrical Engineerin
A Slotted Ring Test Bed for the Study of ATM Network Congestion Management
This thesis addresses issues raised by the proposed Broadband Integrated Services Digital Network which will provide a flexible combination of integrated services traffic through its cell-based Asynchronbus Transport Mode (ATM). The introduction of a cell-based, connection-oriented, transport mode brings with it new technical challenges for network management. The routing of cells, their service at switching centres, and problems of cell congestion not encountered in the existing network, are some of the key issues.
The thesis describes the development of a hardware slotted ring testbed for the investigation of congestion management in an ATM network. The testbed is designed to incorporate a modified form of the ORWELL protocol to control media access. The media access protocol is analysed to give a model for maximum throughput and reset interval under various traffic distributions. The results from the models are compared with measurements carried out on the testbed, where cell arrival statistics are also varied. It is shown that the maximum throughput of the testbed is dependent on both traffic distribution and cell arrival statistics.
The testbed is used for investigations in a heterogeneous traffic environment where two classes of traffic with different cell arrival statistics and quality of service requirements are defined. The effect of prioritisation, media access protocol, traffic intensity, and traffic source statistics were investigated by determining an Admissible Load Region (ALR) for a network station. Conclusions drawn from this work suggest that there are many problems associated with the reliable definition of an ALR because of the number of variable parameters which could shift the ALR boundary. A suggested direction for further work is to explore bandwidth reservation and the concept of equivalent capacity of a connection, and how this can be linked to source control parameters
Non-Intrusive Measurement in Packet Networks and its Applications
PhDNetwork measurementis becoming increasingly important as a meanst o assesst he performanceo f
packet networks. Network performance can involve different aspects such as availability, link
failure detection etc, but in this thesis, we will focus on Quality of Service (QoS). Among the
metrics used to define QoS, we are particularly interested in end-to-end delay performance.
Recently, the adoption of Service Level Agreements (SLA) between network operators and their
customersh as becomea major driving force behind QoS measurementm: easurementi s necessaryt o
produce evidence of fulfilment of the requirements specified in the SLA.
Many attempts to do QoS based packet level measurement have been based on Active Measurement,
in which the properties of the end-to-end path are tested by adding testing packets generated from
the sending end. The main drawback of active probing is its intrusive nature which causes extraburden
on the network, and has been shown to distort the measured condition of the network. The
other category of network measurement is known as Passive Measurement. In contrast to Active
Measurement, there are no testing packets injected into the network, therefore no intrusion is caused.
The proposed applications using Passive Measurement are currently quite limited. But Passive
Measurement may offer the potential for an entirely different perspective compared with Active
Measurements
In this thesis, the objective is to develop a measurement methodology for the end-to-end delay
performance based on Passive Measurement. We assume that the nodes in a network domain are
accessible.F or example, a network domain operatedb y a single network operator. The novel idea is
to estimate the local per-hop delay distribution based on a hybrid approach (model and
measurement-based)W. ith this approach,t he storagem easurementd ata requirement can be greatly
alleviated and the overhead put in each local node can be minimized, so maintaining the fast
switching operation in a local switcher or router.
Per-hop delay distributions have been widely used to infer QoS at a single local node. However, the
end-to-end delay distribution is more appropriate when quantifying delays across an end-to-end path.
Our approach is to capture every local node's delay distribution, and then the end-to-end delay
distribution can be obtained by convolving the estimated delay distributions. In this thesis, our
algorithm is examined by comparing the proximity of the actual end-to-end delay distribution with
the estimated one obtained by our measurement method under various conditions. e. g. in the
presence of Markovian or Power-law traffic. Furthermore, the comparison between Active
Measurement and our scheme is also studied.
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Network operators may find our scheme useful when measuring the end-to-end delay performance.
As stated earlier, our scheme has no intrusive effect. Furthermore, the measurement result in the
local node can be re-usable to deduce other paths' end-to-end delay behaviour as long as this local
node is included in the path. Thus our scheme is more scalable compared with active probing
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 component’s 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
Design, Modeling, and Analysis for MAC Protocols in Ultra-wideband Networks
Ultra-wideband (UWB) is an appealing transmission technology for
short-range, bandwidth demanded wireless communications. With the
data rate of several hundred megabits per second, UWB demonstrates
great potential in supporting multimedia streams such as
high-definition television (HDTV), voice over Internet Protocol
(VoIP), and console gaming in office or home networks, known as the
wireless personal area network (WPAN). While vast research effort
has been made on the physical layer issues of UWB, the corresponding
medium access control (MAC) protocols that exploit UWB technology
have not been well developed.
Given an extremely wide bandwidth of UWB, a fundamental problem on
how to manage multiple users to efficiently utilize the bandwidth is
a MAC design issue. Without explicitly considering the physical
properties of UWB, existing MAC protocols are not optimized for
UWB-based networks. In addition, the limited processing capability
of UWB devices poses challenges to the design of low-complexity MAC
protocols. In this thesis, we comprehensively investigate the MAC
protocols for UWB networks. The objective is to link the physical
characteristics of UWB with the MAC protocols to fully exploit its
advantage. We consider two themes: centralized and distributed UWB
networks.
For centralized networks, the most critical issue surrounding the
MAC protocol is the resource allocation with fairness and quality of
service (QoS) provisioning. We address this issue by breaking down
into two scenarios: homogeneous and heterogeneous network
configurations. In the homogeneous case, users have the same
bandwidth requirement, and the objective of resource allocation is
to maximize the network throughput. In the heterogeneous case, users
have different bandwidth requirements, and the objective of resource
allocation is to provide differentiated services. For both design
objectives, the optimal scheduling problem is NP-hard. Our
contributions lie in the development of low-complexity scheduling
algorithms that fully exploit the characteristics of UWB.
For distributed networks, the MAC becomes node-based problems,
rather than link-based problems as in centralized networks. Each
node either contends for channel access or reserves transmission
opportunity through negotiation. We investigate two representative
protocols that have been adopted in the WiMedia specification for
future UWB-based WPANs. One is a contention-based protocol called
prioritized channel access (PCA), which employs the same mechanisms
as the enhanced distributed channel access (EDCA) in IEEE 802.11e
for providing differentiated services. The other is a
reservation-based protocol called distributed reservation protocol
(DRP), which allows time slots to be reserved in a distributed
manner. Our goal is to identify the capabilities of these two
protocols in supporting multimedia applications for UWB networks. To
achieve this, we develop analytical models and conduct detailed
analysis for respective protocols. The proposed analytical models
have several merits. They are accurate and provide close-form
expressions with low computational effort. Through a cross-layer
approach, our analytical models can capture the near-realistic
protocol behaviors, thus useful insights into the protocol can be
obtained to improve or fine-tune the protocol operations. The
proposed models can also be readily extended to incorporate more
sophisticated considerations, which should benefit future UWB
network design
Performance Modeling and Analysis of Wireless Local Area Networks with Bursty Traffic
The explosive increase in the use of mobile digital devices has posed great challenges in the design and implementation of Wireless Local Area Networks (WLANs). Ever-increasing demands for high-speed and ubiquitous digital communication have made WLANs an essential feature of everyday life. With audio and video forming the highest percentage of traffic generated by multimedia applications, a huge demand is placed for high speed WLANs that provide high Quality-of-Service (QoS) and can satisfy end user’s needs at a relatively low cost. Providing video and audio contents to end users at a satisfactory level with various channel quality and current battery capacities requires thorough studies on the properties of such traffic. In this regard, Medium Access Control (MAC) protocol of the 802.11 standard plays a vital role in the management and coordination of shared channel access and data transmission. Therefore, this research focuses on developing new efficient analytical models that evaluate the performance of WLANs and the MAC protocol in the presence of bursty, correlated and heterogeneous multimedia traffic using Batch Markovian Arrival Process (BMAP). BMAP can model the correlation between different packet size distributions and traffic rates while accurately modelling aggregated traffic which often possesses negative statistical properties.
The research starts with developing an accurate traffic generator using BMAP to capture the existing correlations in multimedia traffics. For validation, the developed traffic generator is used as an arrival process to a queueing model and is analyzed based on average queue length and mean waiting time. The performance of BMAP/M/1 queue is studied under various number of states and maximum batch sizes of BMAP. The results clearly indicate that any increase in the number of states of the underlying Markov Chain of BMAP or maximum batch size, lead to higher burstiness and correlation of the arrival process, prompting the speed of the queue towards saturation.
The developed traffic generator is then used to model traffic sources in IEEE 802.11 WLANs, measuring important QoS metrics of throughput, end-to-end delay, frame loss probability and energy consumption. Performance comparisons are conducted on WLANs under the influence of multimedia traffics modelled as BMAP, Markov Modulated Poisson Process and Poisson Process. The results clearly indicate that bursty traffics generated by BMAP demote network performance faster than other traffic sources under moderate to high loads.
The model is also used to study WLANs with unsaturated, heterogeneous and bursty traffic sources. The effects of traffic load and network size on the performance of WLANs are investigated to demonstrate the importance of burstiness and heterogeneity of traffic on accurate evaluation of MAC protocol in wireless multimedia networks.
The results of the thesis highlight the importance of taking into account the true characteristics of multimedia traffics for accurate evaluation of the MAC protocol in the design and analysis of wireless multimedia networks and technologies
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