Abstract: This invention provides method and apparatus for ancillary data in a wavelength division multiplexed (WDM) system. According to the invention, a low bit rate channel is provided over a amplitude modulated sub-carrier that is in turn used to amplitude intensity modulate an optical data signal that is output from a transmitter in the network. Data carried by the low bit rate channel can by used by another network element (NE) to determine the identity of the channel source, thereby allowing the NE to verify its connectivity to that source via the network. This invention is particularly useful in metropolitan optical networks (MON) where inexpensive methods of determining network connectivity are required.

Abstract: A mean optical power controller that controls power using a voltage controlled optical attenuator (VCOA) is disclosed. This controller uses a control loop in which a signal indicative of the present optical power level is compared to a signal indicative of the desired optical power level, with the difference then being used as input into the VCOA. This controller generates the required variety of signals indicative of the desired optical power level, or reference signals, without having to rely on a CPU. It does this by storing in a local storage means the voltage-values of the reference signals required to realize each supported user-defined optical power level. During the operation of the controller, the voltage-value corresponding to each selected power-level is passed to one or more DACs, where it is converted into a reference signal.

Abstract: The present invention provides a novel tributary protection system for a telecommunications system employing multiplexed lines. To overcome problems with separate line controllers which select the multiplexers to be used, the invention teaches a system wherein each tributary channel interfaces with the multiplexers Mux 1, Mux 2 via a protection device MPD which can switch the tributaries between a first multiplex Mux 1 and a second multiplex Mux 2 when the performance of the system employing the operational multiplexer Mux 1 has been degraded.