Multicast Routing in Optical Access Networks

Multicast Routing in Optical Access Networks

Miklós Molnár (IRISA-INSA, France), Fen Zhou (IRISA-INSA, France) and Bernard Cousin (IRISA-Université de Rennes I, France)
DOI: 10.4018/978-1-60566-707-2.ch008
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Abstract

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.
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Introduction

Recent advances in communication technology have resulted in multicast applications playing an important part in everyday Internet traffic. Data transmission generated by multicast multimedia services as Video-On-Demand, High Definition TV diffusion, Video-Conferences, Distance Learning and Online-Games requires large bandwidth, while QoS (Quality of Service) parameters such as end-to-end delay and jitter must be tolerated. From the white paper of the European Information & Communications Technology Industry Association (EICTA) on Next Generation Networks and Next Generation Access, high speed network access is characterized as (a) the availability of symmetrical access (b) instant communication (no latency) and (c) simultaneous applications (EICTA, 2008). All-optical networks show promise as an infrastructure that can guarantee dependability, flexibility, high bandwidth and QoS for users of multicast applications. All-optical networks have optical access network component directly connected to the mesh optical backbone. The huge capacity of fibers and light based routing in optical switches provide end-users with large bandwidth connections to the network. The most promising technology corresponds to wavelength division multiplexing (WDM). The transmission of data can be organized in either a connection based or a burst switched manner (Qiao & Yoo, 1999). Aggregation techniques and time division multiplexing can be applied to enhance overall network performance. In currently implemented solutions the optical switch configuration is performed via an independent control plane or a fixed-tuned wavelength channel for control messages. This control plane enables precise and thus efficient management of the optical network.

From the point of view of network operators and access providers, access network technology should offer a flexible solution at low cost. Low cost can be achieved with the use of passive equipment and a simple topology (for example a star). The huge capacity of an optical infrastructure currently allows wastage of network resources. However, in the long run a better utilization of network resources may be an important operator objective. The network should thus offer the possibility to manage resources and to balance network load. The dependability of the network is also a fundamental property for operators and users. Currently, optical access network technology is widely based on PONs (Passive Optical Networks), but Ethernet point-to-point and active Ethernet solutions are also present in the market. PONs contain passive elements. They are simple, easy to install and do not require an electrical power supply. A typical FTTx access network implemented with PONs is star based and contains splitters. The most significant drawback of star topologies is their vulnerability. Absolute dependability is a critical and fundamental requirement for modern communication networks. Dependable network services cannot be provided without redundancies in the network topology. Thus, dependable access networks must contain, at least in their core part, redundant edges and nodes, thus producing cycle or mesh topologies.

Multicast routing is not specifically analyzed for current access networks. However, the coexistence of many multicast sessions raises some important problems. For instance, in a star topology the intelligent allocation of wavelengths among multicast sessions can optimize the use of network resources (Sheu & Huang, 1997; Sivalingam, Bogineni, & Dowd, 1992). In a mesh topology the light-tree structure can be introduced. Dependable multicasting is made possible using light-trees because they can be replaced entirely or partially when some network elements fail. In our analysis, we suppose that future optical access networks will be heterogeneous and meshed. This implies that the network topology has some active and configurable switches, and provides sufficient redundancy to offer dependable services with a high level of flexibility for efficient resource management. Moreover, precise configuration of the lightpaths and light-trees enhances the security of the network because data is not broadcast as in a star topology. Multicast routing in heterogeneous and mesh optical access networks (which contain active switches and passive elements) can play an important role in the all-optical networks of the future. Optical switch architectures and optical fiber characteristics introduce some specific constraints which must be taken into account by the routing algorithm. Moreover, the throughput of the network depends strongly on the efficiency of the routing algorithms. For these reasons, we propose a survey of multicast routing algorithms under the typical physical constraints of wavelength switched optical access networks.

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