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Technology

The original LIVE-NET system was based on an early technology domestic cable TV distribution system. With this sort of network it makes economic sense to send as many channels as possible down each fibre. At the time of its development during the mid 80's the maximum bit rate that could be carried on optical fibre was ~140Mbps. This is equivalent to a single high quality uncompressed digital video signal. Unless complex and hence expensive equipment were used to compress the digital signal there would have been a practical limit of one video channel per fibre. As a result an analogue frequency modulation system was used which enabled four high quality analogue signals and a fifth data channel to be carried on one optical fibre.

Due to drift in the transmission and reception equipment this did not prove to be too successful in practice. In particular the fifth data channel on the longest link (RHBNC to Senate House 42km with a repeater at 25km) was never very reliable as a result of which one of the video channels had to be used to carry data.

The analogue section of LIVE-NET 2 is based on a single channel contribution network using RS1000 standard equipment. This technology was developed for surveillance and security systems (such as those used in city centres) where only a single channel needs to transmitted per fibre. RS100 provides a slightly better quality video signal and eliminates the problems of equipment drift which occurred with the previous equipment.

Some of the fibres in the new system are used to carry data at the G703 standard (as used by LIVE-NET 1). Since the fibres used to transmit data are not shared with other signals reliability is expected to be far higher than with the previous system.

The cost of fibre is not a large factor in determining the overall cost of a fibre based video distribution system. With present day technology four single channel fibres are as cheap as a single multiplexed four channel fibre. Multiplexing becomes cheaper than using single fibres when transmitting between 6 and eight channels.

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