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Comprehensive and Detailed Explanation From Nokia Optical Networking Fundamentals:

While technologies like WSS (Wavelength Selective Switches) and coherent transmission (100G/200G/400G+) significantly improve the efficiency and reach of a network, the most direct way to increase the total transportable volume of services in a mesh topology is toupgrade link capacityorinstall new physical links. In Nokia optical planning, upgrading link capacity typically involves moving from a lower-rate system (like 10G) to a higher-rate system (like 100G or 400G) or increasing the number of available wavelengths by expanding from a 40-channel to an 80-channel or 96-channel C-band system.

Adding new links (new fiber spans) creates more degrees in the mesh, providing more paths for traffic and increasing the overall aggregate bandwidth of the network.Option Arefers to flexibility (ROADM functionality) rather than raw capacity.Option B(PRC) relates to survivability and availability, not capacity expansion. WhileOption C(coherent transmission) is a powerful method for increasing capacity per wavelength, it is not the "only" way, as adding more fiber (spatial multiplexing) or more channels (spectral density) are also primary methods for scaling a mesh network to handle more services.

It can be implemented through the use of a Y-cable or an optical protection switch (OPS) card, which allows for the switching of traffic to a secondary path in the event of a failure on the primary path. This type of protection is commonly used to protect against fiber cuts and other types of physical layer failures in the optical transport network.

Comprehensive and Detailed Explanation From Nokia Optical Networking Fundamentals:

In the context of optical networking fundamentals, anoptical switch(often referred to as a Photonic Switch or Layer 0 switch) is defined as a device that routes an optical signal—composed of photons—from an input port to one or more output ports without converting it into an electrical signal. This process is known astransparent switching. It operates entirely within the optical domain, maintaining the integrity of the lightwave regardless of the data rate or protocol being carried (e.g., SDH, Ethernet, or OTN).

It is important to distinguish this from Option D, which describes anElectrical or ODU Switch(Layer 1). In a device like the Nokia 1830 PSS-24x, signals are converted to electrical format (O-E-O) to be switched at the ODU (Optical Data Unit) level via a central fabric. While this provides "any-to-any" grooming, a trueoptical switch(like a WSS found in ROADMs) simply steers the light. The primary advantage of an optical switch is its ability to handle massive amounts of bandwidth with extremely low latency and lower power consumption compared to electrical switching, as it avoids the overhead of repeated O-E-O conversions at intermediate network nodes.

According to the Nokia Optical Networking documentation, a Shared Risk Group (SRG) is defined as "a set of network resources that share a common failure risk. When a resource in an SRG fails, the other resources in the group are also affected." This can include fibers, boards, nodes, and other network resources. The SRG concept is used in network design and protection mechanisms to ensure survivability and minimal impact on service in case of a failure.