227 research outputs found
Multicasting in WDM Single-Hop Local Lightwave Networks
In modem networks, the demand for bandwidth and high quality of service (QoS) requires the efficient utilisation of network resources such as transmitters, receivers and
channel bandwidth. One method for conserving these resources is to employ efficient implementations of multicasting wherever possible. Using multicasting, a source sending a message to multiple destinations may schedule a single transmission which can then be broadcasted to multiple destinations or forwarded from one destination to another, thus conserving the source transmitter usage and channel bandwidth. This thesis investigates the behaviour of single-hop WDM optical networks when they carry multicast traffic. Each station in the network has a fixed-wavelength transceiver and is set to operate on its own unique wavelength as a control channel. Each station also has a tuneable wavelength transceiver in order to transmit or receive signals to or from all the other stations. A transmission on each channel is broadcasted by a star coupler to all nodes. Multicasting in single-hop WDM networks has been studied with different protocols. This thesis studies the multicasting performance adopting receiver collision avoidance (RCA) protocol as a multicasting protocol. This study takes into consideration the effect of the tuneable transceiver tuning time which is the time required to switch from one wavelength to another, and the propagation time required by a packet to propagate from one node to another. The strategy in RCA protocol is that nodes request transmission time by sending a control packet at the head of their queues. Upon receipt of this information all nodes run a deterministic distributed algorithm to schedule the transmission of the multicast packet. With the control information, nodes determine the earliest time at which all the members of the multicast group can receive the packet and the earliest time at which it can be transmitted. If a node belongs to the multicast group addressed in the control packet, its receiver must
become idle until all nodes in the group have tuned to the appropriate wavelength to receive the packet. This problem leads to poor transmission and consequently low channel
utilisation. However, throughput degradation due to receiver conflicts decreases as the multicast size increases. This is because for a given number of channels, the likelihood of a receiver being idle decreases as the number of intended recipients per transmission increases.
The number of wavelengths available in a WDM network continues to be a major constraint. Thus in order to support a large number of end users, such networks must use and reuse wavelengths efficiently. This thesis also examines the number of wavelengths needed to support multicasting in single-hop optical networks
Design And Analysis Of a Multi-channel Optical Fibre Lan Based On Modified Csma/cd Protocol
Nowadays, optical communication is widely employed by telecommunication
providers in the whole world due to its ability to support high bit rate applications. The
urge to provide end-to-end fibre connectivity arises to overcome the bottleneck problem
that occurs when packets are transmitted on the slower speed medium such as copper. In
optical transmission, bandwidth utilisation can be improved further by using multiple
wavelengths or channels in a single fibre.
This thesis discusses the implementation of multiple wavelengths technique for
Local Area Network (LAN) environment. It proposes a new Ethernet-based protocol that
uses multiple wavelengths for transmission, which runs on a single fibre. Ethernet/IEEE
802.3 is chosen because of its widespread employment in today's network and the
ability of extending the transmission rate up to gigabit transmission. Even though light
does not collide with each other, receiver contention might occur if more than one signal
arrives at the receiver at the same time. Therefore, some arbitration mechanism is
needed to synchronise the transmission and the tuning time of the respective transmitter and receiver. The proposed design is based on the physical bus topology with n number
of connected nodes and m number of operating wavelengths. All nodes are able to listen
to all wavelengths. A fast control unit is used, which is responsible for packet
scheduling.
The packets are scheduled based on a pre-computed time. Both transmitter and
receiver will be asked to tune to the· allocated wavelength. The transmitter can start
transmitting and the receiver will start tuning at a specified time. Control packets are
used for handshaking purposes. The main operation is placed at the control unit so that
no added complexity is experienced by the receiver. Thus, this technique further reduces
the cost. A suitable range of channels is obtained from the result. The network
performance is evaluated against several design parameters by comparing the
performance of each channel. The result shows a significant improvement whereby the
throughput and efficiency are increased and average delay is minimised compared to the
conventional system
Wavelength and time division multiplexing with lightpath trespassing for all-optical star local area networks
Many medium access control protocols have been proposed for optical wavelength division multiplexing local area networks with a star topology. These protocols range from those based on the concept of fixed-assignment of communication subchannels, such as TDMA (Time Division Multiple Access); reservation of communication subchannels, such as DAS (Dynamic Allocation Scheme); or random-access to communication subchannels, such as DT-WDMA (Dynamic Time-Wavelength Division Multiple Access). In addition various hybrid protocols have been considered, for example, protocols incorporating both fixed-assignment and reservation rules, such as HTDM (Hybrid TDM). This thesis is on a novel hybrid protocol of fixed-assignment and random-access called "WTDMA with lightpath trespassing". This protocol combines the most desirable aspects of fixed-assignment and random-access protocols, while limiting their drawbacks. The performance of different versions of the protocol are analysed both mathematically and by stochastic simulation. The obtained results justify the introduction of the WTDMA with trespassing protocol, and indicate the situations where its use is advantageous
A Distributed Asynchronous Transmission Access Strategy for Optical Single-Hop LANs: An Analytical Performance Study
In this paper, we introduce an optical passive network architecture suitable for wavelength division multiplexing local area networks (LANs) which use a separate control wavelength. The data wavelengths are organized into several sets, while the access rights over them are distributedly determined aiming to totally expunge the packets collisions on the wavelengths and at destination. The proposed access algorithm pertains to the asynchronous transmission schemes. Thus, it is simple enough since it does not require any synchronization among the stations, providing high efficiency especially under high data rates (100 Gbps and beyond). The performance is evaluated through exhaustive analysis, whilst closed mathematical formulas provide the performance measures. The comparative study proves that the proposed wavelengths organization into sets strategy along with the access scheme significantly improves the performance. Especially, the throughput improvement is proven to be higher as the number of sets increases, and more than 100% even by organizing the wavelengths into only two sets, for diverse numbers of data wavelengths, data wavelengths sets and data packets size. Finally, the proposed study could be applied to optical passive single-hop LANs such as intra-rack data center networks or local institutional or enterprise networks
CSMA/CA using pilot tone on PON
Jorden Yeong-Tswen, Tse.Thesis (M.Phil.)--Chinese University of Hong Kong, 2003.Includes bibliographical references (leaves 76-76).Abstracts in English and Chinese.ACKNOWLEDGEMENTS --- p.2ABSTRACT --- p.3摘要 --- p.4CONTENTS --- p.5Chapter CHAPTER 1: --- INTRODUCTION --- p.8Chapter 1.1. --- First Mile Evolution --- p.8Chapter 1.2. --- Access: Passive Optical Network (PON) --- p.10Chapter 1.2.1. --- ATM-PON (APON) --- p.13Chapter 1.2.2. --- Ethernet PON (EPON) --- p.14Chapter 1.3. --- Problem Definition and Possible Solutions --- p.16Chapter 1.3.1. --- Wavelength Division Multiplexing (WDM) --- p.17Chapter 1.3.2. --- Time Division Multiplexing (TDM) --- p.18Chapter 1.3.3. --- Sub-carrier Multiplexing (SCM) & Frequency Division Multiplexing (FDM) --- p.20Chapter 1.3.4. --- Code Division Multi Access (CDMA) --- p.20Chapter 1.4. --- Thesis Organization --- p.20Chapter CHAPTER 2: --- BACKGROUND --- p.22Chapter 2.1. --- EPON Solution:- MPCP --- p.22Chapter 2.2. --- CSMA/CD on PON --- p.26Chapter 2.3. --- Motivation --- p.28Chapter CHAPTER 3: --- CSMA/CA PROTOCOL USING PILOT TONE ON PON --- p.29Chapter 3.1. --- Basic Protocol Description --- p.29Chapter 3.1.1. --- With No Contention --- p.31Chapter 3.1.2. --- With Contention --- p.32Chapter 3.1.3. --- With Contention and Winner --- p.33Chapter 3.2. --- Simulation --- p.35Chapter 3.2.1. --- Effect of Loading on Network Utilization --- p.37Chapter 3.2.2. --- Effect of Network Size on Utilization --- p.39Chapter 3.2.3. --- Delay Performance --- p.41Chapter 3.2.4. --- Effect of Distance from Remote Node --- p.44Chapter 3.2.5. --- Effect of Maximum Packet Duration on Utilization and Delay --- p.45Chapter 3.3. --- Conclusions --- p.47Chapter CHAPTER 4: --- PROTOCOL ENHANCEMENT ON VARIOUS ASPECTS --- p.48Chapter 4.1. --- Utilization Enhancement --- p.48Chapter 4.1.1. --- Improvement on Network Utilization --- p.50Chapter 4.1.2. --- Network Delay Performance --- p.52Chapter 4.1.3. --- Conclusions --- p.53Chapter 4.2. --- Capture Effect --- p.53Chapter 4.2.1. --- Solution by Varying Ts --- p.54Chapter 4.2.2. --- Simulations --- p.55Chapter 4.2.3. --- Conclusions --- p.58Chapter 4.3. --- Introducing Cos to existing network --- p.59Chapter 4.3.1. --- Principle --- p.59Chapter 4.3.2. --- Simulation Model --- p.60Chapter 4.3.3. --- Utilization Performance --- p.61Chapter 4.3.4. --- Delay Performance --- p.64Chapter 4.3.5. --- Conclusions --- p.68Chapter CHAPTER 5: --- CONCLUSIONS --- p.69Chapter 5.1. --- Thesis Summary --- p.69Chapter 5.2. --- Future Work --- p.71REFERENCES --- p.7
HFR Networks: New concepts and technologies
To study the main trends which drive the merging of fiber and wireless technologies in access networks. As the hybrid radio networks constitute a new and emerging field of knowledge it is difficult to get a clear picture of their main building blocks and basic technologies and concepts. Due to the lack of reference texts with a basic entry level, in this PFC we aim at carrying out a thorough study of the related literature in order to establish a clear classification of systems and techniques, to clarify the basic terms and to study the specific transmission characteristics of hybrid radio links, both from a point to point as well as from a networks management perspective.
• Steaming from the above, the main physical effects and phenomena around optical and wireless technologies will be reviewed and the basic analytical as well as computer and simulation tools will be presented along with some simulation examples showing relevant fiber-radio transmission effects and techniques.
• The main driver will be to help newcomers to the field to get a fast understanding of the basic related ideas and analysis techniques for hybrid fiber-radio networks.
• In this regard the key building blocks to implement the HFR's networks will be identified. These should include underlying concepts such as working frequencies, general structure for the coexistence of wireless and fiber technologies, the network components and topologies proposed, as well as the hybrid link's features, characterizing parameters and main impairments that degrade the quality of transmission
Multicast Routing In Optical Access Networks
Widely available broadband services in the Internet require high capacity access networks. Only optical networking is able to efficiently provide the huge bandwidth required by multimedia applications. Distributed applications such as Video-Conferencing, HDTV, VOD and Distance Learning are increasingly common and produce a large amount of data traffic, typically between several terminals. Multicast is a bandwidth-efficient technique for one-to-many or many-to-many communications, and will be indispensable for serving multimedia applications in future optical access networks. These applications require robust and reliable connections as well as the satisfaction of QoS criteria. In this chapter, several access network architectures and related multicast routing methods are analyzed. Overall network performance and dependability are the focus of our analysis
Virtualisation and resource allocation in MECEnabled metro optical networks
The appearance of new network services and the ever-increasing network traffic and number
of connected devices will push the evolution of current communication networks towards the
Future Internet.
In the area of optical networks, wavelength routed optical networks (WRONs) are evolving
to elastic optical networks (EONs) in which, thanks to the use of OFDM or Nyquist WDM,
it is possible to create super-channels with custom-size bandwidth. The basic element in
these networks is the lightpath, i.e., all-optical circuits between two network nodes. The
establishment of lightpaths requires the selection of the route that they will follow and the
portion of the spectrum to be used in order to carry the requested traffic from the source to
the destination node. That problem is known as the routing and spectrum assignment (RSA)
problem, and new algorithms must be proposed to address this design problem.
Some early studies on elastic optical networks studied gridless scenarios, in which a slice
of spectrum of variable size is assigned to a request. However, the most common approach to
the spectrum allocation is to divide the spectrum into slots of fixed width and allocate multiple,
consecutive spectrum slots to each lightpath, depending on the requested bandwidth. Moreover,
EONs also allow the proposal of more flexible routing and spectrum assignment techniques,
like the split-spectrum approach in which the request is divided into multiple "sub-lightpaths".
In this thesis, four RSA algorithms are proposed combining two different levels of
flexibility with the well-known k-shortest paths and first fit heuristics. After comparing the
performance of those methods, a novel spectrum assignment technique, Best Gap, is proposed
to overcome the inefficiencies emerged when combining the first fit heuristic with highly
flexible networks. A simulation study is presented to demonstrate that, thanks to the use of
Best Gap, EONs can exploit the network flexibility and reduce the blocking ratio.
On the other hand, operators must face profound architectural changes to increase the
adaptability and flexibility of networks and ease their management. Thanks to the use of
network function virtualisation (NFV), the necessary network functions that must be applied
to offer a service can be deployed as virtual appliances hosted by commodity servers, which
can be located in data centres, network nodes or even end-user premises. The appearance of
new computation and networking paradigms, like multi-access edge computing (MEC), may
facilitate the adaptation of communication networks to the new demands. Furthermore, the
use of MEC technology will enable the possibility of installing those virtual network functions
(VNFs) not only at data centres (DCs) and central offices (COs), traditional hosts of VFNs, but
also at the edge nodes of the network. Since data processing is performed closer to the enduser,
the latency associated to each service connection request can be reduced. MEC nodes
will be usually connected between them and with the DCs and COs by optical networks.
In such a scenario, deploying a network service requires completing two phases: the
VNF-placement, i.e., deciding the number and location of VNFs, and the VNF-chaining,
i.e., connecting the VNFs that the traffic associated to a service must transverse in order to
establish the connection. In the chaining process, not only the existence of VNFs with available
processing capacity, but the availability of network resources must be taken into account to
avoid the rejection of the connection request. Taking into consideration that the backhaul of
this scenario will be usually based on WRONs or EONs, it is necessary to design the virtual
topology (i.e., the set of lightpaths established in the networks) in order to transport the tra c
from one node to another. The process of designing the virtual topology includes deciding the
number of connections or lightpaths, allocating them a route and spectral resources, and finally
grooming the traffic into the created lightpaths.
Lastly, a failure in the equipment of a node in an NFV environment can cause the
disruption of the SCs traversing the node. This can cause the loss of huge amounts of data
and affect thousands of end-users. In consequence, it is key to provide the network with faultmanagement
techniques able to guarantee the resilience of the established connections when a
node fails.
For the mentioned reasons, it is necessary to design orchestration algorithms which solve
the VNF-placement, chaining and network resource allocation problems in 5G networks
with optical backhaul. Moreover, some versions of those algorithms must also implements
protection techniques to guarantee the resilience system in case of failure.
This thesis makes contribution in that line. Firstly, a genetic algorithm is proposed to solve
the VNF-placement and VNF-chaining problems in a 5G network with optical backhaul based
on star topology: GASM (genetic algorithm for effective service mapping). Then, we propose
a modification of that algorithm in order to be applied to dynamic scenarios in which the
reconfiguration of the planning is allowed. Furthermore, we enhanced the modified algorithm
to include a learning step, with the objective of improving the performance of the algorithm.
In this thesis, we also propose an algorithm to solve not only the VNF-placement and
VNF-chaining problems but also the design of the virtual topology, considering that a WRON
is deployed as the backhaul network connecting MEC nodes and CO. Moreover, a version
including individual VNF protection against node failure has been also proposed and the
effect of using shared/dedicated and end-to-end SC/individual VNF protection schemes are
also analysed.
Finally, a new algorithm that solves the VNF-placement and chaining problems and
the virtual topology design implementing a new chaining technique is also proposed.
Its corresponding versions implementing individual VNF protection are also presented.
Furthermore, since the method works with any type of WDM mesh topologies, a technoeconomic
study is presented to compare the effect of using different network topologies in
both the network performance and cost.Departamento de Teoría de la Señal y Comunicaciones e Ingeniería TelemáticaDoctorado en Tecnologías de la Información y las Telecomunicacione
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