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

Resilient optical multicasting utilizing cycles in WDM optical networks

High capacity telecommunications of today is possible only because of the presence of optical networks. At the heart of an optical network is an optical fiber whose data carrying capabilities are unparalleled. Multicasting is a form of communication in wavelength division multiplexed (WDM) networks that involves one source and multiple destinations. Light trees, which employ light splitting at various nodes, are used to deliver data to multiple destinations. A fiber cut has been estimated to occur, on an average, once every four days by TEN, a pan-European carrier network. This thesis presents algorithms to make multicast sessions survivable against component failures. We consider multiple link failures and node failures in this work. The two algorithms presented in this thesis use a hybrid approach which is a combination of proactive and reactive approaches to recover from failures. We introduce the novel concept of minimal-hop cycles to tolerate simultaneous multiple link failures in a multicast session. While the first algorithm deals only with multiple link failures, the second algorithm considers the case of node failure and a link failure. Two different versions of the first algorithm have been implemented to thoroughly understand its behavior. Both algorithms were studied through simulators on two different networks, the USA Longhaul network and the NSF network. The input multicast sessions to all our algorithms were generated from power efficient multicast algorithms that make sure the power in the receiving nodes are at acceptable levels. The parameters used to evaluate the performance of our algorithms include computation times, network usage and power efficiency. Two new parameters, namely, recovery times and recovery success probability, have been introduced in this work. To our knowledge, this work is the first to introduce the concept of minimal hop cycles to recover from simultaneous multiple link failures in a multicast session in optical networks

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

Survivable multicasting in WDM optical networks

Opportunities abound in the global content delivery service market and it is here that multicasting is proving to be a powerful feature. In WDM networks, optical splitting is widely used to achieve multicasting. It removes the complications of optical-electronic-optical conversions [1]. Several multicasting algorithms have been proposed in the literature for building light trees. As the amount of fiber deployment increases in networks, the risk of losing large volumes of data traffic due to a fiber span cut or due to node failure also increases. In this thesis we propose heuristic schemes to make the primary multicast trees resilient to network impairments. We consider single link failures only, as they are the most common cause of service disruptions. Thus our heuristics make the primary multicast session survivable against single link failures by offering alternate multicast trees. We propose three algorithms for recovering from the failures with proactive methodologies and two algorithms for recovering from failures by reactive methodologies. We introduce the new and novel concept of critical subtree. Through our new approach the proactive and reactive approaches can be amalgamated together using a criticality threshold to provide recovery to the primary multicast tree. By varying the criticality threshold we can control the amount of protection and reaction that will be used for recovery. The performance of these five algorithms is studied in combinations and in standalone modes. The input multicast trees to all of these recovery heuristics come from a previous work on designing power efficient multicast algorithms for WDM optical networks [1]. Measurement of the power levels at receiving nodes is indeed indicative of the power efficiency of these recovery algorithms. Other parameters that are considered for the evaluation of the algorithms are network usage efficiency, (number of links used by the backup paths) and the computation time for calculating these backup paths. This work is the first to propose metrics for evaluating recovery algorithms for multicasting in WDM optical networks. It is also the first to introduce the concept of hybrid proactive and reactive approach and to propose a simple technique for achieving the proper mix

Dynamic Optical Networks for Data Centres and Media Production

This thesis explores all-optical networks for data centres, with a particular focus on network designs for live media production. A design for an all-optical data centre network is presented, with experimental verification of the feasibility of the network data plane. The design uses fast tunable (< 200 ns) lasers and coherent receivers across a passive optical star coupler core, forming a network capable of reaching over 1000 nodes. Experimental transmission of 25 Gb/s data across the network core, with combined wavelength switching and time division multiplexing (WS-TDM), is demonstrated. Enhancements to laser tuning time via current pre-emphasis are discussed, including experimental demonstration of fast wavelength switching (< 35 ns) of a single laser between all combinations of 96 wavelengths spaced at 50 GHz over a range wider than the optical C-band. Methods of increasing the overall network throughput by using a higher complexity modulation format are also described, along with designs for line codes to enable pulse amplitude modulation across the WS-TDM network core. The construction of an optical star coupler network core is investigated, by evaluating methods of constructing large star couplers from smaller optical coupler components. By using optical circuit switches to rearrange star coupler connectivity, the network can be partitioned, creating independent reserves of bandwidth and resulting in increased overall network throughput. Several topologies for constructing a star from optical couplers are compared, and algorithms for optimum construction methods are presented. All of the designs target strict criteria for the flexible and dynamic creation of multicast groups, which will enable future live media production workflows in data centres. The data throughput performance of the network designs is simulated under synthetic and practical media production traffic scenarios, showing improved throughput when reconfigurable star couplers are used compared to a single large star. An energy consumption evaluation shows reduced network power consumption compared to incumbent and other proposed data centre network technologies