A metro network links customers and nodes within a city. At the nodes, traffic maybe routed on to other customers or on to the Core network. Requirements:
Flexibility: A metro needs to be flexible, as there will be a need to reconfigure the network as business grows or the demands of customer’s change.
Reliability: Ring topology will usually be used to allow automatic traffic re-routing in the event of a fiber break.
Bandwidth: Large bandwidths will still be used in the metro network as customers are buying 10Gbit/s services today. Metro DWDM systems with 40 channels are being used.
Costs: Digging a metro network is an expensive process in a city centre. It is far harder to dig up a city street or pavement than a roadside verge for a core network cable route.
Cable: A cable with a high fiber count is essential, as space with the ductwork will need to be used as efficiently as possible.
Fiber: Existing metro networks built before 2000 will use ordinary singlemode fiber that conforms to ITU standard G652. This type of fiber is designed for use with 1310nm lasers. The latest metro DWDM systems will work using this fiber but only at lower data rates (up to 2.5Gbit/s) or over relatively short distances. New fibers are now available that will optimise the spectrum in the 1550nm range.
Topology: Rings are used to connect customers back to the hub or node sites. This gives diversity in case of a failure at some point in the network.
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