Optical TDM transmission system

Claim 2

In an optical time division multiplexed digital transmission system, a method of tributary channel identification comprising; the step of applying, at a multiplexer which multiplexes a plurality of tributary digital channels on to a single multiplexed digital channel, a tributary channel identification signal to modulate said single multiplexed digital channel, which channel identification signal has a fundamental frequency which is phase-matched with the bit rate of one of the tributary channels; the step of extracting, at a demultiplexer which demultiplexes the single multiplexed digital channel into its plurality of tributary channels, said channel identification signal, and employing it to generate a clock; and the step of employing, at said demultiplexer, the clock to demultiplex said single multiplexed digital channel into its plurality of tributary channels, routing each specific tributary channel into an associated output port specific to that specific tributary channel.

Claim 3

In an optical time division multiplexed digital transmission system, a method of tributary channel identification as claimed in claim 1, wherein the tributary channel identification signal amplitude modulates the multiplexed channels.

Claim 4

In an optical time division multiplexed digital transmission system, a method of tributary channel identification comprising; the step of applying, at a multiplexer which multiplexes a plurality of tributary digital channels on to a single multiplexed digital channel, a tributary channel identification signal to modulate said single multiplexed digital channel, which channel identification signal has a fundamental frequency which is phase-matched with a subharmonic of the bit rate of one of the tributary channels; the step of extracting at a demultiplexer which demultiplexes the single multiplexed digital channel into its plurality of tributary channels, said channel identification signal, and employing it to generate a clock; and the step of employing, at said demultiplexer, the clock to demultiplex said single multiplexed digital channel into its plurality of tributary channels, routing each specific tributary channel into an associated output port specific to that specific tributary channel.

Claim 5

In an optical time division multiplexed digital transmission system, a method of tributary channel identification comprising; the step of applying, at a multiplexer which multiplexes a plurality of tributary digital channels on to a single multiplexed digital channel, a tributary channel identification signal to modulate said single multiplexed digital channel, which channel identification signal has a fundamental frequency which is phase-matched with a subharmonic of the bit rate of one of the tributary channels; the step of extracting at a demultiplexer which demultiplexes the single multiplexed digital channel into its plurality of tributary channels, said channel identification signal, and employing it to generate a clock; and the step of employing, at said demultiplexer, the clock to demultiplex said single multiplexed digital channel into its plurality of tributary channels, routing each specific tributary channel into an associated output port specific to that specific tributary channel.

Claim 6

In en optical time division multiplexed digital transmission system, a method of tributary channel identification as claimed in claim 3, wherein the tributary channel identification signal amplitude modulates the multiplexed channels.