g (WDM) and/or dense wavelength division multiplexing (DWDM) is fairly self-explanatory in that it is based on modulating and detecting multiple optical channels within a discrete band of optical frequencies. These techniques have become more applicable as dispersion compensation techniques have improved. In parallel, optical splitting techniques have been developed for the local access domain that have allowed a single fibre to be shared between multiple premises and multiple users. The splitting techniques are unpowered, hence the description passive optical network. Laser sources are relatively narrowband devices, whereas optical receivers are wideband. In practical terms this means that wavelength demultiplexers need to be installed in user premises. This would be an issue for example for Open Reach in the UK as and when they decided to upgrade from their present GPON 14 network, to a WDM PON network as the demultiplexers are expensive and temperature sensitive. A GPON network as presently implemented typically conforms to the ITU T G.984 stan- dard and delivers asymmetric service based on 2.488 Gbps of downstream bandwidth and 14 gigabit passive optical network. Physical Layer Connectivity 1.244 Gbps of upstream bandwidth supporting time multiplexed voice, Ethernet and ATM. The physical reach of these networks is of the order of 20 km. PTP networks, as the name implies, have dedicated point-to-point fibre for each user or at least for each end point, which means more fibre than a PON SO the fibre cost is higher, though this is offset by not having to have wavelength multiplexers/demultiplexers. A PTP network uses more duct space, which can be a problem if the duct space is already full up. PTP networks use a multiplexer that splits the signal into transmit and receive wavelengths, either 1310/1550 nm or 1310/1490 nm, supporting symmetrical services and specified to operate over 10 km. Passive optical networks and point-to-point fibre access networks are therefore the two competing deployment options for loca