Optical communications – Duplex – Wavelength division
Reexamination Certificate
1999-09-07
2004-04-27
Tweel, Jr., John A. (Department: 2632)
Optical communications
Duplex
Wavelength division
C398S074000, C385S050000
Reexamination Certificate
active
06728484
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates in general to fiber optic communication systems, and more particularly to a method and apparatus for providing channel provisioning and optical wavelength division multiplexing (WDM) networks.
2. Description of Related Art
In broadband communication networks, data are increasingly transmitted through glass or optical fiber lines in the form of optical signals. Over the last two decades, optical fibers have revolutionized the communications industry. Meanwhile, continuous innovations in optical components have made it possible to design and implement higher and higher bit-rate systems. Consequently, fiber designs continue to evolve in almost every segment of the network infrastructure.
The major driver for all this activity is the urgent need for more capacity. The late 1990s have seen an enormous surge in the amount of traffic on telecom networks. Networks whose capacity looked demand-proof only two or three years ago are hard-pressed to cope with this demand. Not only is traffic growing, but also there is a fundamental change in the nature of this traffic. In the 80s and early 90s, the majority of network traffic consisted of voice. The growth in this traffic was, and still is, fairly predictable. However, the growth in data traffic is now far outstripping the growth in voice, spurred on by the Internet and corporate data applications. The advent of affordable higher bandwidth access mechanisms such as digital subscriber line technology will serve to accelerate this growth. Voice and data are already equal on some routes, and it is clear that in the next decade data will dominate telecom networks.
Wavelength division multiplexing (WDM) is a technique for transmitting traffic over fiber in multiple channels. Traditional optical fiber transmission uses light of a single wavelength (i.e. color). In contrast, WDM combines multiple wavelengths of light into a single, multiplexed signal for transmission along a fiber. Each channel utilizes the full capacity of the fiber being used. WDM thus creates ‘virtual fiber’: carrying traffic over, for example, four WDM wavelength channels boosts the capacity of an installed fiber by four times.
WDM is now being used by telecommunication companies worldwide to dramatically boost the capacity of installed optical fiber cables. However, the effect WDM will have on the telecommunication industry is much more complex, ranging far beyond simple capacity increase in networks, even though the basic principle of the technology is very simple. Accordingly, WDM is emerging as an essential technology for allowing telecommunication networks to endure the telecommunication demands of the next century. The future growth of the Internet, the creation of new high bandwidth applications, the economics of the bandwidth market itself and the development of broadband networking are all inextricably linked with WDM technology.
As optical technology advances and the optical layer materializes in telecommunications networks, new challenges have emerged for engineers and network planners. Just as synchronous optical networks (SONET) introduced new design issues, such as optimized traffic patterns and restoration schemes, implementation of the optical layer with wavelength add-drop multiplexers (WADMs) has new difficulties. Telecommunication companies, as well as many smaller companies and new entrants to the telecommunication business are planning to deploy WADMs in their network. Thus, it is important that these new difficulties are addressed.
Perhaps the most fundamental issue associated with WADMs in optical networks is end-to-end wavelength span design. As some wavelengths are dropped and added while others pass through a site, network designers must consider the span for each wavelength to insure the required performance. Planners must predict the performance of each channel individually, especially considering that the channels added will be of higher quality than those passing through.
One of the more complex span designs is that of mesh architectures. A mesh architecture is a design where each channel may take a dynamically routed path around failures. When utilizing mesh architectures, all possible scenarios need to be evaluated to insure that for a single or multiple fiber cuts or failures, traffic on a channel is not lost because of unacceptable optical performance.
When adding and dropping individual wavelengths in the network, it becomes imperative for providers to be able to manage the network with wavelength granularity. Providers must be able to monitor the condition of each wavelength and maintain network traffic in the same manner that electrical paths are managed today. The complexity of managing wavelengths also depends on whether the provider is using dedicated wavelength paths (WP) or “virtual” wavelength paths (VWP) in which the signal can change to another wavelength along the route. Ideally, the optical network will provide end to end services entirely in the optical domain, without ever converting signals into the electrical format.
The basic element in the optical network is the wavelength. As many wavelengths of signals are transported across the network, it becomes important to manage and switch each one individually. One of the benefits of optical networks is that it allows the network architecture for each wavelength to be different. For example, one wavelength may be established in the network to be part of a ring configuration, while another wavelength, using the same physical network, can be provisioned as point-to-point system. The flexibility of provisioning the network a wavelength at a time has led to two definitions of end-to-end services: wavelength paths and virtual wavelength paths.
The simplest implementation of a wavelength service in the optical network is a wavelength path (WP). Using a WP, a signal enters and exits the optical layer at the same wavelength, without ever changing to a different wavelength throughout the network. Essentially a wavelength is dedicated to connect the two endpoints together. This kind of design is typically much easier to plan for from an engineering perspective, because planners will know which wavelength will be used on all parts of the optical span. Designing is simply an issue of determining the path and calculating performance, as discussed above.
Although a WP is simple to implement, it can impose some limitations on the bandwidth available in the network and the cost of implementing it. One method to overcome this limitation is by using a “virtual” wavelength path (VWP) in which a signal path can travel on different wavelengths throughout the network. By avoiding a dedicated wavelength for an end-to-end connection, the network can reuse and optimize wavelengths to provide the greatest amount of capacity. The flexibility provided by VWPs comes at a cost: VWPs introduce more difficulty into the network design. For networks with a large number of all-optical paths, especially in metropolitan or access networks, VWPs can introduce a large number of possible optical path sets to be calculated and planned for.
Although the main driver for WDM today is the need to increase network capacity and relieve network congestion, WDM is part of a much bigger story of the evolution of electrical networks to optical networks. Eventually, WDM is expected to be used to route traffic on individual wavelengths in all levels of the network, significantly increasing flexibility. This transition will create an optical layer. The optical layer is a new networking layer in which wavelength channels are processed and routed only by optical equipment, just as electronic multiplexers, cross connects and switches handle semi-permanent digital channels in the synchronous digital hierarchy (SDH)/SONET and asynchronous transfer mode (ATM) layers of today's networks. As suggested above, this will involve the deployment of optical add-drop multiplexers, enabling WDM ring architectures to be constructed. In the longer term this will also re
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