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Optical Satellite Networking
Published in Hamid Hemmati, Near-Earth Laser Communications, 2020
Optical WDM networking with wavelength routing is based on the concept of lightpath, i.e., a continuous optical connection that is established between a source node and a destination node (satellites in this case) via a number of links (ISLs in this case) and intermediate nodes without requiring processing of traffic in the intermediate nodes [Baroni et al., 1997]. Several lightpaths can use the same ISL by being at different wavelength through WDM. Wavelength routing or, in other words, optical circuit switching, is then used onboard each satellite to properly direct the lightpaths from an input ISL to an output one or to the downlink based on a fixed traffic matrix (Figure 11.5). Optical networks based on these principles are currently deployed in terrestrial fiber networks throughout the world [Mukherjee, 2006].
Fiber-Optic Network without WDM
Published in Partha Pratim Sahu, Fundamentals of Optical Networks and Components, 2020
In this network, the end nodes are equipped with wavelength crossconnect ((WXC) for switching one wavelength of any output fiber to the required input fiber) and transceivers tunable to required wavelengths. Message is sent from one node to another node using a wavelength continuous route called lightpath, without requiring any optical–electronics–optical conversion and buffering. Intermediate nodes route the lightpath using WXCs. The architecture of WXC is shown in Figure 1.8. A lightpath is an all-optical communication path between two nodes. It is identified as a physical path, and the wavelength on this path can be realized as a high-bandwidth pipe capable of transmitting several gigabits per second. The requirement that the same wavelength must be used on all the links of selected route is called wavelength continuity constraint. One fiber cannot contain two lightpaths of the same wavelength. This is called distinct wavelength assignment constraint. However, two lightpaths can use the same wavelength if they use disjoint sets of links. This property is called wavelength reuse. Packet switching can be supported in WDM optical communication by virtual topology (a set of lightpaths or optical layer) is imposed over a physical topology (not broadcast system) by setting the OXCs in each interval nodes. At each interval node, the packet is converted to electronic form and retransmitted on another wavelength.
Traffic Grooming in Optical Networks
Published in Partha Pratim Sahu, Advances in Optical Networks and Components, 2020
where ti = time period between the ith event (connection arrival or departure) and (i + 1)th event, ρi = load carried by the network during the time period ti, and γi = the total number of wavelength links that do not change during the time period ti. If in the network every connection is assigned full wavelength-channel capacity (i.e., no capacity is wasted) and is assigned the shortest path (in hop distance), the RER is equal to unity. A connection considers the following policies: The connection is accommodated through the least-cost path. The cost of a lightpath link is equal to the overall cost of the fiber links it traverses.If there are multiple least-cost paths and the connection does not require full wavelength-channel capacity, the required path is chosen as per the minimal number of free wavelength links.If there are multiple least-cost paths and the bandwidth requirement of the connection and full wavelength-channel capacity, the route is chosen as per the minimal number of electronic grooming fabrics.
Routing and wavelength assignment with protection: A quadratic unconstrained binary optimization approach enabled by Digital Annealer technology
Published in IISE Transactions, 2023
Oylum Şeker, Merve Bodur, Hamed Pouya
Wavelength-routed networks form a broad class of WDM networks, and can be considered as a set of nodes joined by fiber links. The communication between a pair of nodes is established through lightpaths; this is referred to as connecting the two nodes. A lightpath is an optical communication channel between two nodes in the network, and is comprised of a path (route) and a wavelength. A typical problem arising in wavelength-routed networks is the Routing and Wavelength Assignment (RWA) problem. Given a set of connection requests between pairs of nodes, the RWA problem decides which requests to grant, i.e., provision a lightpath, such that no two allocated lightpaths with the same wavelength traverse a common fiber link, to prevent interference.