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We note that this chapter is not entirely within the scope of this book, which focuses on layers higher than the physical layer. However, due to the novelty of optical networks, it is important to have some knowledge of the underlying WDM technology. It is not necessary to read this chapter in detail in order to understand the subsequent chapters on optical networks; the key sections to study are the introductory section and the section on components.
Chapter 9: Wavelength routing optical networks
In this chapter, we explore different aspects of a wavelength routing optical networks. We first start with a description of the main features of a wavelength routing network and introduce the ever important concept of a lightpath and the concept of traffic grooming, which permits multiple users to share the same lightpath. We also present protection and restoration schemes used to provide carrier grade reliability.
Information on a lightpath is typically transmitted using SONET/SDH framing. Ethernet frames can also be transmitted over an optical network. In the future, it is expected that information will be transmitted over the optical network using the new ITU-T G.709 standard, part of which is described in this chapter. G.709, also known as the digital wrapper, permits the transmission of IP packets, Ethernet frames, ATM cells, and SONET/SDH synchronous data.
The rest of the chapter is dedicated to the control plane for wavelength routing networks. We present different types of control plane architectures, and then describe the generalized MPLS (GMPLS) architecture and the OIF user network interface (UNI). GMPLS is an extension of MPLS and it was designed with a view to applying the MPLS label-switching techniques to time-division multiplexing (TDM) networks and wavelength routing networks in addition to packet-switching networks. The OIF UNI specifies signaling procedures for clients to automatically create, delete, and query the status of a connection over a user network interface.
Chapter 10: Optical Burst Switching (OBS)
In a wavelength routing optical network, a connection has to be set up before data will be transmitted. The resources remain allocated to this connection even when there is no
traffic transmitted. In view of this, connection utilization can be low when the traffic is bursty. In this chapter, we examine a different optical networking scheme, which is better suited for the transmission of bursty traffic. Because the data is transmitted in bursts, this scheme is known as optical burst switching (OBS).
OBS has not yet been standardized, but it is regarded as a viable solution to the problem of transmitting bursty traffic over an optical network. In an OBS network, the user data is collected at the edge of the network, then sorted by destination address, and then grouped into bursts of variable size. Prior to transmitting a burst, a control packet is sent into the optical network in order to set up a bufferless optical connection all of the way to the destination. After a delay, the data burst is transmitted optically without waiting for a positively acknowledgment from the destination node. The connection is set up uniquely for the transmission of a single burst, and is torn down after the burst has been transmitted. That is, a new connection has to be set up each time a burst has to be transmitted through the optical network.
In this chapter, we first present briefly the main features of optical packet switching, a technology that preceded OBS. Then, we describe in detail the main features of OBS and present the Jumpstart signaling protocol. This is a proof-of-concept protocol developed to demonstrate the viability of OBS.
Chapter 11: Access networks
An access network is a packet-switching network that provides high-speed Internet connectivity to homes. Access networks will also provide additional services, such as voice over IP (VoIP), voice over ATM (VoATM), and video on demand. Access networks have different features and requirements than LANs, MANs, and WANs. Currently, there are two different access networks; one is provided over the telephone twisted pair, and the other over the cable network. New access networks, such as the ATM passive optical network (APON) and Ethernet-based and wireless-based access networks, are beginning to emerge.
Telephone operators provide currently high-speed access to the Internet over the twisted pair in addition to basic telephone services. Video on demand and voice over IP or ATM will also be provided in the future. A family of modems known as x-type digital subscriber line (xDSL) has been developed to provide high-speed access to the Internet over the telephone line. Of the xDSL modems, the asymmetric DSL (ADSL) is the most popular one.
Cable operators provide currently access to the Internet, voice over IP, and video on demand over their cable network in addition to the distribution of TV channels. The cable-based access network uses the data-over-cable service interface specification (DOCSIS).