389 research outputs found
Quality of service modeling and analysis for carrier ethernet
Today, Ethernet is moving into the mainstream evolving into a carrier grade technology. Termed as Carrier Ethernet it is expected to overcome most of the\ud
shortcomings of native Ethernet. It is envisioned to carry services end-to-end serving corporate data networking and broadband access demands as well as backhauling wireless traffic. As the penetration of Ethernet increases, the offered Quality of Service (QoS) will become increasingly important and a distinguishing factor between different service providers. The challenge is to meet the QoS requirements of end applications such as response times, throughput, delay and jitter by managing the network resources at hand. Since Ethernet was not designed to operate in large public networks it does not possess functionalities to address this issue. In this thesis we propose and analyze mechanisms which improve the QoS performance of Ethernet enabling it to meet the demands of the current and next generation services and applications.\u
Quality aspects of Internet telephony
Internet telephony has had a tremendous impact on how people communicate.
Many now maintain contact using some form of Internet telephony.
Therefore the motivation for this work has been to address the quality aspects
of real-world Internet telephony for both fixed and wireless telecommunication.
The focus has been on the quality aspects of voice communication,
since poor quality leads often to user dissatisfaction. The scope of the work
has been broad in order to address the main factors within IP-based voice
communication.
The first four chapters of this dissertation constitute the background
material. The first chapter outlines where Internet telephony is deployed
today. It also motivates the topics and techniques used in this research.
The second chapter provides the background on Internet telephony including
signalling, speech coding and voice Internetworking. The third chapter
focuses solely on quality measures for packetised voice systems and finally
the fourth chapter is devoted to the history of voice research.
The appendix of this dissertation constitutes the research contributions.
It includes an examination of the access network, focusing on how calls are
multiplexed in wired and wireless systems. Subsequently in the wireless
case, we consider how to handover calls from 802.11 networks to the cellular
infrastructure. We then consider the Internet backbone where most of our
work is devoted to measurements specifically for Internet telephony. The
applications of these measurements have been estimating telephony arrival
processes, measuring call quality, and quantifying the trend in Internet telephony
quality over several years. We also consider the end systems, since
they are responsible for reconstructing a voice stream given loss and delay
constraints. Finally we estimate voice quality using the ITU proposal PESQ
and the packet loss process.
The main contribution of this work is a systematic examination of Internet
telephony. We describe several methods to enable adaptable solutions
for maintaining consistent voice quality. We have also found that relatively
small technical changes can lead to substantial user quality improvements.
A second contribution of this work is a suite of software tools designed to
ascertain voice quality in IP networks. Some of these tools are in use within
commercial systems today
Switching techniques for broadband ISDN
The properties of switching techniques suitable for use in broadband networks have been investigated. Methods for evaluating the performance of such switches have been reviewed. A notation has been introduced to describe a class of binary self-routing networks. Hence a technique has been developed for determining the nature of the equivalence between two networks drawn from this class. The necessary and sufficient condition for two packets not to collide in a binary self-routing network has been obtained. This has been used to prove the non-blocking property of the Batcher-banyan switch. A condition for a three-stage network with channel grouping and link speed-up to be nonblocking has been obtained, of which previous conditions are special cases.
A new three-stage switch architecture has been proposed, based upon a novel cell-level algorithm for path allocation in the intermediate stage of the switch. The algorithm is suited to hardware implementation using parallelism to achieve a very short execution time. An array of processors is required to implement the algorithm The processor has been shown to be of simple design. It must be initialised with a count representing the number of cells requesting a given output module. A fast method has been described for performing the request counting using a non-blocking binary self-routing network. Hardware is also required to forward routing tags from the processors to the appropriate data cells, when they have been allocated a path through the intermediate stage. A method of distributing these routing tags by means of a non-blocking copy network has been presented.
The performance of the new path allocation algorithm has been determined by simulation. The rate of cell loss can increase substantially in a three-stage switch when the output modules are non-uniformly loaded. It has been shown that the appropriate use of channel grouping in the intermediate stage of the switch can reduce the effect of non-uniform loading on performance
Traffic Profiles and Performance Modelling of Heterogeneous Networks
This thesis considers the analysis and study of short and long-term traffic patterns of
heterogeneous networks. A large number of traffic profiles from different locations and
network environments have been determined. The result of the analysis of these patterns
has led to a new parameter, namely the 'application signature'. It was found that these
signatures manifest themselves in various granularities over time, and are usually unique
to an application, permanent virtual circuit (PVC), user or service. The differentiation of
the application signatures into different categories creates a foundation for short and long-term
management of networks. The thesis therefore looks from the micro and macro
perspective on traffic management, covering both aspects.
The long-term traffic patterns have been used to develop a novel methodology for network
planning and design. As the size and complexity of interconnected systems grow steadily,
usually covering different time zones, geographical and political areas, a new
methodology has been developed as part of this thesis. A part of the methodology is a new
overbooking mechanism, which stands in contrast to existing overbooking methods
created by companies like Bell Labs. The new overbooking provides companies with
cheaper network design and higher average throughput. In addition, new requirements like
risk factors have been incorporated into the methodology, which lay historically outside
the design process. A large network service provider has implemented the overbooking
mechanism into their network planning process, enabling practical evaluation.
The other aspect of the thesis looks at short-term traffic patterns, to analyse how
congestion can be controlled. Reoccurring short-term traffic patterns, the application
signatures, have been used for this research to develop the "packet train model" further.
Through this research a new congestion control mechanism was created to investigate how
the application signatures and the "extended packet train model" could be used. To
validate the results, a software simulation has been written that executes the proprietary
congestion mechanism and the new mechanism for comparison. Application signatures for
the TCP/IP protocols have been applied in the simulation and the results are displayed and
discussed in the thesis. The findings show the effects that frame relay congestion control
mechanisms have on TCP/IP, where the re-sending of segments, buffer allocation, delay
and throughput are compared. The results prove that application signatures can be used
effectively to enhance existing congestion control mechanisms.AT&T (UK) Ltd, Englan
Statistical multiplexing and connection admission control in ATM networks
Asynchronous Transfer Mode (ATM) technology is widely employed for the transport of network traffic, and has the potential to be the base technology for the next generation of global communications. Connection Admission Control (CAC) is the effective traffic control mechanism which is necessary in ATM networks in order to avoid possible congestion at each network node and to achieve the Quality-of-Service (QoS) requested by each connection. CAC determines whether or not the network should accept a new connection. A new connection will only be accepted if the network has sufficient resources to meet its QoS requirements without affecting the QoS commitments already made by the network for existing connections. The design of a high-performance CAC is based on an in-depth understanding of the statistical characteristics of the traffic sources
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Operational support systems for satellite communications
The role of satellite communications is changing from providing bandwidth linking network operators interconnections towards providing IP enabled communications to end users. This migration from few high-value routes towards many low-value routes means that integration and automation of processes with terrestrial networks becomes critical in driving down unit costs. Integration and automation is necessary on all planes: user, control and management. In satellite communications, management aspects, underpinned by Operational Support Systems (OSS) have received the least research attention, making this a valuable topic for study. In most areas, OSS for satellite systems are similar to other domains. However there are some notable areas of difference which have been the focus of this research. The eTOM business framework, developed by the TMF, has been used to highlight aspects of OSS unique to satellite. Since satellite capacity represents the highest operational cost of a satellite route, effective management while minimising the overhead traffic is critical. The transmission of IP packets is assumed and the real-time measurement of QoS parameters such as packet delay and loss emerged as the most important differences. A number of approaches to QoS measurement are feasible, however the use of trace packets is most promising especially for high network loads. An experiment compares the results from simulations, mathematical models and from a test network, using Poisson and self-similar traffic flows. The relationship between measurement accuracy and trace packet intensity is explored and the measurement response time to steps in traffic load is estimated. It is discovered that measurement accuracy improves as the queue load increases, in contrast to alternative approaches such as sampling of user packets. The response time to steps depends upon the degree of self-similarity and is generally longer than the times recommended by standards. A pragmatic approach to management of different modes is proposed where the measurement method is changed depending on the load
Dynamic wavelength allocation in IP/WDM metro access networks
Ankara : The Department of Electrical and Electronics Engineering and the Institute of Engineering and Science of Bilkent University, 2008.Thesis (Ph.D.) -- Bilkent University, 2008.Includes bibliographical references leaves 132-139.Increasing demand for bandwidth and proliferation of packet based traffic
have been causing architectural changes in the communications infrastructure.
In this evolution, metro networks face both the capacity and dynamic adaptability
constraints. The increase in the access and backbone speeds result in high
bandwidth requirements, whereas the popularity of wireless access and limited
number of customers in metro area necessitates traffic adaptability. Traditional
architecture which has been optimized for carrying circuit-switched connections,
is far from meeting these requirements. Recently, several architectures have been
proposed for future metro access networks. Nearly all of these solutions support
dynamic allocation of bandwidth to follow fluctuations in the traffic demand.
However, reconfiguration policies that can be used in this process have not been
fully explored yet. In this thesis, dynamic wavelength allocation (DWA) policies
for IP/WDM metro access networks with reconfiguration delays are considered.
Reconfiguration actions incur a cost since a portion of the capacity becomes idle
in the reconfiguration period due to the signalling latencies and tuning times of
optical transceivers. Exact formulation of the DWA problem is developed as a
Markov Decision Process (MDP) and a new cost function is proposed to attain
both throughput efficiency and fairness. For larger problems, a heuristic approach
based on first passage probabilities is developed. The performance of the method
is evaluated under both stationary and non-stationary traffic conditions. The
effects of relevant network and traffic parameters, such as delay and flow size are
also discussed. Finally, performance bounds for the DWA methods are derived.Yetginer, EmrePh.D
Allocation des ressources et des solutions pour économiser de l'énergie dans les réseaux optiques d'accÚs
In this thesis, general overview about PON systems is presented and existing PON mechanisms and classification are investigated. After, a novel dynamic bandwidth allocation algorithm for EPON is introduced. This proposed algorithm is named as âHalf Cycling Dynamic Bandwidth Allocation-hcDBAâ by the inspiration of its half cycling processing mode. Later, an improvement of hcDBA algorithm with early prediction mechanism is presented. As a result statement of the study, hcDBA algorithm performs better than existing mechanism in terms of packet loss ratio and access delays. Beside, simulation traffic behavior of EPONâs upstream channel has been investigated in order to support the decision of selecting suitable traffic generator in further studies. Energy conversation is one of the hot topics in telecommunication networks. Access networks constitute remarkable portion of the total energy consumption in telecommunication networks. ITU-T and IEEE organizations published recommendation for energy conversation in PONs. While, total energy consumption of ONUs is more than other equipment in fix access network the standards and most of the researches focused on saving energy at ONU side. In this thesis I focused on an energy efficiency method based on energy conversation on OLT side. The proposed method save energy by dynamically moving OLT cards to deep sleep mode according to the incoming and outgoing traffic loadsDans ce travail de thĂšse, un aperçu gĂ©nĂ©ral sur les systĂšmes PON est prĂ©sentĂ© et sont Ă©tudiĂ©s les mĂ©canismes et classification PON existants. AprĂšs, nous introduisons notre premiĂšre contribution qui est un algorithme d'allocation dynamique de bande passante pour EPON. Cet algorithme proposĂ© est dĂ©signĂ© comme «hcDBA». Par la suite, une amĂ©lioration de l'algorithme de hcDBA avec mĂ©canisme de prĂ©diction prĂ©coce est prĂ©sentĂ©e. Notre simulation montre bien que notre algorithme hcDBA est performant comparĂ© aux mĂ©canismes existants en termes de taux de perte de paquets et de dĂ©lai dâaccĂšs. Dans notre seconde contribution, nous sommes intĂ©ressĂ©s au problĂšme de consommation dâĂ©nergie qui est un sujet dâactualitĂ© dans les rĂ©seaux de tĂ©lĂ©communication. Les Ă©tudes montrent aujourdâhui que les rĂ©seaux d'accĂšs constituent une partie remarquable de la consommation totale d'Ă©nergie dans les rĂ©seaux de tĂ©lĂ©communication. Les organisations ITU-T et IEEE ont publiĂ© la recommandation pour la conversation de l'Ă©nergie pour les rĂ©seaux PONs. Bien que, la consommation totale d'Ă©nergie des nĆuds ONU est plus importantes que d'autres Ă©quipements dans le rĂ©seau d'accĂšs fixe, les normes et la plupart des travaux de recherches ont portĂ© sur les Ă©conomies d'Ă©nergie du cĂŽtĂ© de ONU. Dans cette thĂšse, nous sommes concentrĂ©s sur une mĂ©thode d'efficacitĂ© Ă©nergĂ©tique basĂ©e sur la conservation de l'Ă©nergie du cĂŽtĂ© de lâOLT. La mĂ©thode proposĂ©e permet dâĂ©conomiser de l'Ă©nergie en dĂ©plaçant dynamiquement des cartes dâOLT en mode de sommeil profond en fonction des charges de trafic entrant et sortan
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