Time slot arrangements for local area network systems

DETAILED DESCRIPTION According to the invention there is provided a communication system comprising a common communication medium and a plurality of subscribers interface units each connected to the common medium and each interface unit includes a data transmission arrangement for transmitting data information signals onto the medium and a data reception arrangement for receiving data information signals from the medium, the medium being arranged to operate in accordance with a time division multiplex in which each time slot includes an active period for the transmission of a data burst of data information signals and a transit period and each interface unit includes internal timing arrangements and means for observing the timing of traffic burst on the highway and means for adjusting the internal timing arrangements so that the time slot timing cycle within the interface unit corresponds with that of the data on the highway.
The data signals, which may include speech, take any well known form, such as digital signals in Manchester code or analogue or digital modulated carrier, sometimes know as broadband, and the medium may be electrical cable, optic fibre or broadcast by electromagnetic, ultrasonic or infrared, by suitable system design.
The internal timing arrangements are arranged to produce a time slot marker which nominally occurs at the mid-point of the transit time of each time slot.
Typically time slot marker adjustment occurs in accordance with the following:
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If own marker would occur
Action
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(i) clear of existing traffic
Continue as before
(ii) in the first half of a
Move own t.
s.
to
data burst start of data burst
(iii) in the second half of a
Move own t.
s.
to end
data burst of data burst
(iv) in unbroken continuous
Continue as before
data
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This arrangement achieves the near simultaneous occurence of time slot markers by all interface units be they busy or free, by each unit observing the timing of traffic bursts on the highway and adjusting the internal timing time slot marker to occur in the time between data bursts of existing traffic (i