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1. Let us assume that in a WDM point-to-point link each wavelength is used to transmit SONET/ SDH frames at the rate of OC-48/STM-16 (i.e., 2488 Mbps). Calculate the total capacity of the link for W = 1, 16, 32, 128, 512, 1024. Repeat these calculations assuming that the rate
OPTICAL FIBERS AND COMPONENTS
of transmission over a single wavelength is: OC-192/STM-64 (9953 Mbps), OC-768/STM-256 (39,813Mbps).
2. Browse the Internet to find out the maximum number of wavelengths which is currently commercially available in a WDM point-to-point link.
3. What are the differences between a single-mode and a multi-mode fiber? The standard for the 1-Gbps Ethernet makes use of both single-mode and multi-mode fibers. Browse the Internet to find out how each of these fiber modes are used.
4. Explain what is attenuation and dispersion.
5. Explain the terms transparent switch and opaque switch.
6. Draw a three-stage Clos network. What are the main differences between a Banyan network and a Clos network? (Hint: for information, check the literature on ATM switch architectures.)
7. Use the 2D MEMS OADM shown in Figure 8.26 to design an OADM that serves a single fiber
with 64 wavelengths. Each 2D MEMS is assumed to have 32 x 32 ports.
Wavelength Routing Optical Networks
Wavelength routing optical networks have been successfully commercialized and standards bodies, such as the IETF, OIF, and ITU-T, are currently active in the development of the standards. A wavelength routing optical network consists of optical cross-connects (OXCs) interconnected with WDM fibers. Transmission of data over this optical network is done using optical circuit-switching connections, known as lightpaths.
In this chapter, we explore different aspects of the 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 data over a synchronous frame structure.
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 was designed to apply 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 and delete a connection over a wavelength routing network. The UNI signaling has been implemented by extending the label distribution protocols, LDP and RSVP.
9.1 WAVELENGTH ROUTING NETWORKS
A wavelength routing (or routed) network consists of OXCs interconnected by WDM fibers. An OXC is an N x N optical switch, with N input fibers and N output fibers (see Section 8.3.5). Each fiber carries W wavelengths. The OXC can optically switch all of the incoming wavelengths of its input fibers to the outgoing wavelengths of its output
Connection-oriented Networks Harry Perros © 2005 John Wiley & Sons, Ltd ISBN: 0-470-02163-2
WAVELENGTH ROUTING OPTICAL NETWORKS
fibers. For instance, it can switch the optical signal on incoming wavelength Xi of input fiber k to the outgoing wavelength Xi of output fiber m. If output fiber m’s wavelength Xi is in use, and if the OXC is equipped with converters, then the OXC can also switch the optical signal of input fiber k’s incoming wavelength Xi to another one of output fiber m’s outgoing wavelength Xj.
In addition to switching individual wavelengths, an OXC can switch a set of contiguous wavelengths (known as a waveband) as a single unit. That is, it can switch a set of contiguous wavelengths of an input fiber to a set of contiguous wavelengths of an output fiber. This can be a desirable OXC feature, because it can reduce the distortion of the individual wavelengths. In addition, an OXC might not have the capability to separate incoming wavelengths that are tightly spaced. In this case, it can still switch them using waveband switching. Finally, an OXC can also switch an entire fiber. That is, it can switch all of the W wavelengths of an input fiber to an output fiber.
There are several technologies available for building an OXC, such as multistage interconnection networks of 3-dB couplers, MEMS, SOA, micro-bubbles and holograms (see Section 8.3.5). New technologies are expected to emerge in the future.