Optical Networks: A Practical Perspective - Part 56. This book describes a revolution within a revolution, the opening up of the capacity of the now-familiar optical fiber to carry more messages, handle a wider variety of transmission types, and provide improved reliabilities and ease of use. In many places where fiber has been installed simply as a better form of copper, even the gigabit capacities that result have not proved adequate to keep up with the demand. The inborn human voracity for more and more bandwidth, plus the growing realization that there are other flexibilities to be had by imaginative use of the fiber, have led people. | 520 Control and Management able to add additional wavelengths up to a designed maximum number without disrupting the operation of the existing wavelengths. Also ideally the failure of one channel shouldn t affect other channels and the failed channel should be capable of being serviced without affecting the other channels. An issue that comes up in this regard is the use of arrayed multiwavelength components versus separate components for individual wavelengths such as multiwavelength laser arrays instead of individual lasers for each wavelength. Using arrayed components can reduce the cost and footprint of the equipment. However if one element in the array fails the entire array will have to be replaced. This reduces the system availability as replacing the array will involve disrupting the operation of multiple channels and not just a single channel. Using arrays also increases the replacement cost of the module. Therefore there is always a trade-off between obtaining reduced cost and footprint on one front against system availability and replacement cost on the other front. We may also want to start out by deploying the equipment in the form of a point-to-point link and later upgrade it to handle ring or other network configurations. We may also desire flexibility in associating specific port cards in the equipment with specific wavelengths. For example it is better to have a system where we can choose the wavelength transmitted out of a port card independently of what slot it is located in. Another problem in WDM systems is the need to maintain an inventory of wavelength-specific spare cards. For example each channel may be realized by using a card with a wavelength-specific laser in it. Thus you would need to stock spare cards for each wavelength. This can be avoided by using a wavelength-selectable or tunable laser on each card instead of a wavelength-specific laser such devices are only now becoming commercially available at reasonable cost. Connection
