What is wdm network




















Using a fiber optic cable as a single lane road is wasteful. Smartoptics solutions allow this road to be used as a multi-lane highway capable of transporting up to 80 simultaneous traffic channels together at once. Expanding capacity. Without building new infrastructure. Wavelength division multiplexing, WDM, has long been the technology of choice for transporting large amounts of data between sites and optimize optical network performance.

Which of the two key WDM technologies is best suited to a given environment depends on the network and user requirements. A closer look at the most common ways of transporting data over a fiber network is by using single channel connectivity, embedded WDM solutions or active WDM platforms.

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A solution fit for purpose. Subscribe Ask the community. Wavelength Division Multiplexing WDM is a fiber-optic transmission technique that enables the use of multiple light wavelengths or colors to send data over the same medium. Two or more colors of light can travel on one fiber, and several signals can be transmitted in an optical waveguide at differing wavelengths or frequencies on the optical spectrum. Only to deploy. Subscribe to get more articles on this topic. Topics Redefining optical networks.

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What is L-band? What is Liquid Spectrum? What is LSO? What is MCP? What is mobile backhaul? As a result, network survivability is a major factor that affects how these networks are designed and operated. The networks need to be designed to handle link or fiber cuts as well as equipment faults. The network may be viewed as consisting of many layers inter-operating with each other, as shown in the above figure.

Different carriers choose different ways of realizing their networks using different combinations of layering strategies.

Incumbent carriers make use of their large installed base of SDH gear and the extensive grooming and monitoring capabilities of digital cross-connects. In contrast, a carrier offering Internet Protocol IP based services seek to have a simplified network infrastructure using IP as the basic transport layer without using SDH. Carriers that distinguish themselves based on quality and diversity of services QOS may use ATM as their transport technology. Underneath these layers is the emerging optical WDM layer, or the optical layer.

The optical layer provides light-paths to higher layers, which may be considered as client layers that make use of the service provided by the optical layer. Light paths are circuit-switched pipes carrying traffic at fairly high bit rates e.

Once they are set up, they remain fairly static over time. OLTs multiplex multiple channels into a single fiber or fiber pair. An OXC, switches and manages large number of channels in a high-traffic node location. We look at the optical layer protection from a services perspective, in terms of the types of services needed to be provided by the optical layer to the higher layer.

We then compare the different optical layer protection schemes that have been proposed in terms of their cost and bandwidth efficiency based on the service mix that must be supported. This is somewhat different, which tend to view optical layer protection as analogous to SDH layer protection. While these layers were all designed to work with other layers, they can also directly operate over fiber, and thus do not depend on other layers to handle the protection and restoration functions.

As a result, each of these layers incorporate its own protection and restoration functions. Thus, the question arises, why do we need the optical layer to provide its own set of protection and restoration mechanisms. Some of the layers operating above the optical layer may not be fully able to provide all the protection functions needed in the network.

For example, the SDH layer was designed to provide comprehensive protection and, therefore, would not rely on the optical layer protection. However, protection techniques in other layers IP or ATM by themselves may not be sufficient to provide adequate network availability in the presence of faults.

There are currently many proposals to operate the IP layer directly over the optical layer without using the SDH layer. While IP incorporates fault tolerance at the routing level, this mechanism is cumbersome and not fast enough to provide adequate QOS.

In this case, it becomes important for the optical layer to provide fast protection to meet the overall availability requirements from the transport layer. Most carriers have huge investments in legacy equipment that does not provide protection mechanisms at all, but cannot be ignored. A seamless introduction of the optical layer between this equipment and the raw fiber offers low-cost upgrade of the infrastructure over long fiber links with increased survivability.

Optical layer protection and restoration may be used to provide an additional level of resilience in the network. For example, many transport networks are designed to handle a single failure at a time, but not multiple failures. Optical restoration can be used to provide resilience against multiple failures. Optical layer protection can be more efficient at handling certain types of failures, such as fiber cuts. A single fiber carries multiple wavelengths of traffic e. The network management system is flooded with large number of alarms generated by each of these independent entities.

If the fiber cut is restored sufficiently quickly by the optical layer, this operational inefficiency can be avoided. Significant cost savings can be obtained by making use of optical layer protection and restoration. It cannot handle all types of faults in the network.

It may not be able to detect all types of faults in the network. The light paths provided by the optical layer may be transparent such that they carry data at a variety of bit rates. The optical layer in this case may in fact be unaware of what exactly is carried on these light paths. As a result, it cannot monitor the traffic to sense degradations, such as increased bit error rates, that would normally invoke a protection switch.

The optical layer protects traffic in units of light paths. It cannot provide different levels of protection to different parts of the traffic being carried on the light path part of the traffic may be high-priority, the other lower priority.

This function must be performed by a higher layer that handles traffic at this finer granularity. There may be link budget constraints that limit the protection capability of the optical layer. For example, the length of the protection route or the number of nodes the protection traffic passes through may be constrained. If the overall network is not carefully engineered, there may be race conditions when the optical layer and the client layer both try to protect traffic against a failure simultaneously.

The technology and protection techniques are yet to be field tested, and full scale deployment of these new protection mechanisms will, therefore, take a few years to happen. Before going into the details of the protection techniques and the trade-offs between them, it is beneficial to define the entities that are protected by the optical layer and the client layer. These entities are shown in the following figure. The ports on the client equipment may fail. In this case, the optical layer cannot protect the client layer by itself.

The cables inside a site may be disconnected, mainly due to human errors. This is considered a relatively likely event. As the gain bandwidth of an optical fiber amplifier is rather limited, a tight wavelength spacing is needed to put a large number of channels into the gain bandwidth.

The need for a tight channel spacing in DWDM technology mainly arises from the relatively narrow gain bandwidth of EDFA compared to the entire optical telecommunication bands. On the other hand, if the transmission distance is less than km and no amplifiers are needed, a wider channel spacing can be an option. A wider channel spacing allows the use of inexpensive components such as:. There are 18 center wavelengths with 20 nm spacing from nm to nm, covering the O-, E-, S-, C- and L-bands. All the 18 wavelengths are not necessarily be used, and in fact, it is very common to use:.

This is mainly because many optical components e. Telecom networks are roughly classified into three categories, the core, metro, and access networks see Figure 4.



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