Network Planning Research Papers - Academia.edu (original) (raw)

Multiplexing several optical channels on a single fiber (Wavelength Division Multiplexing, WDM) has become the preferred transmission technology in transport networks. WDM was first used for point to point configurations to increase capacity of congested links. With WDM links deployed in the network, the need for planning all these new networking capabilities at the optical layer has also been intensified. The amount of traffic going through the nodes is increasing with a dynamic behavior. These functions should be solved by the routing functionality at the optical layer. Optical Add/Drop Multiplexer, OADM, and Optical Cross-Connects, OXC, give the capabilities to terminate a certain wavelength in a given node, and to let the remaining wavelengths go through. Nowadays, all networks and devices are either opaque (with conversions from optical to electrical and back to optical again), or transparent (the conversion to electrical – or upper layers – is only done at the client level, when the signal is extracted). From an operator point of view, Swisscom requires some benefits from the network planning tools to design its optical networks and prepare itself to the future enhancements of the network. Given several inputs , either constant or variable in time, the tools have to perform a suite of operations. They will lead to a set of possible solutions for the network infrastructure at each layer (the inter-layer networking is one crucial aspect to consider). These solutions should be re-entered to the planning process to take into account possible changes in demands, or protocol strategy, or any other input. This modular structure allows the operator to plan different scenarios, and to obtain the best solutions in terms of cost, migration to the new capabilities, traffic increase, and also from a technical point of view. Given the nodes location (points of presence for the network), the cost functions for the network elements and the links, and an estimation of the traffic matrix, the planning tools can deliver the architecture and the dimensioning of the network to transport this traffic, for ring or mesh networks. Then the routing of the wavelengths has to be done in a transparent network. The traffic that goes through the nodes, to the nodes and from them has to be computed, for both transparent and opaque networks. These values will give the designer an estimation to migrate to another technology or to make a grooming function at certain nodes. For specific configurations like rings, the interconnections are not trivial and special wavelengths have to be planned. The optical network also has to protect certain links or connections (demands), so a different algorithm will perform that task. Knowing the spare capacity left after this traffic allocation, the tools can reroute again to converge to a stable configuration. The network availability for network elements and services can be computed at this time in the planning process. Several optimizations could be performed to get the minimum length links, to groom traffic to maximize traffic load, or to obtain minimum link cost, for example. The networking aspects, like the protocols chosen , have to be carefully considered. It would be very interesting to obtain a report that highlights where the problems can appear for a certain configuration, and proposes changes, even at a protocol level, based on the cost of the equipment or on the inter-networking aspects. Different solutions for the given inputs can be obtained, and the network planner has to select the one that best fits to his demand. A way to select the best solution could be to re-evaluate the solutions under slightly different inputs, like a higher traffic forecast, and see if the new solutions are similar to the previous ones. This iterative process could also be useful to plan migration strategies.