Multiplex communications – Wide area network – Packet switching
Patent
1984-06-29
1986-05-27
Olms, Douglas W.
Multiplex communications
Wide area network
Packet switching
370100, H04J 306
Patent
active
045920516
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a method and apparatus in a telecommunication system for activating subscriber terminals in a digital subscriber connection including a line terminal assigned to the station side of the system, a network terminal assigned to the subscriber installation and one or more subscriber terminals, the line terminal being connected to a central clock pulse oscillator at the station side, and the network terminal and subscriber terminals containing local clock pulse oscillators.
BACKGROUND ART
It is already known to switch over subscriber terminals from an idling state to an activated state with the aid of special activation signals in the form of DC signals.
DISCLOSURE OF INVENTION
A problem occuring in the DC activation of subscriber terminals is the requirement of detecting different DC levels to enable distinguishing between idle condition currents and activating currents. Since the idle condition current is used to maintain certain functions in the terminal during the idling state also, the level of the idle condition current is thus limited by the activation signal level, there being limits to how low the former may fall and how high the latter may rise. This results in a small margin between the different voltage levels and thereby increases sensitivity to interference. Furthermore, in possible standardization one will be tied to a technique which is not optimized for the future.
The method and apparatus in accordance with the invention are characterized by the claims, and solve the problem by the activation being carried out digitally in loops with the aid of binary code words.
The system includes, as mentioned, a line terminal LT on the station side of a connection, a network terminal NT assigned to the subscriber installation and one or more subscriber terminals ST. (See FIG. 1)
Activation can be performed in synchronous or asynchronous/plesiochronous operation, and may be initiated either from the subscriber side (the subscriber terminal ST) or from the station side (the line terminal LT).
In activation started from the subscriber terminal ST, terminal ST sends an activation request AR giving rise to temporary synchronization of the clock in the network terminal NT with the clock from the terminal ST, and also the temporary activating of the network terminal NT. The clock signal in the terminal ST is plesiochronous in relation to the clock signal in the line terminal LT, which terminal is connected to the station clock functioning as master. With activation of the network terminal, the activation request is sent from it to the line terminal LT which, on received activation request via the station (EX), sends out the activation order AO to the terminal NT in the same way as the activation was started from the line terminal LT. The activation-synchronization signal received in the terminal NT gives rise to the final activation of the terminal, its synchronization to the clock pulse from the line terminal, and transmission, of equal signals to the subscriber terminal ST. An activation-synchronization signal received in the terminal ST from the terminal NT provides the final activation of the former and its synchronization to the clock pulse from the line terminal LT.
In starting activation from the line terminal LT no activation request is sent, but an activation order is sent, as previously mentioned, directly to the terminals NT and ST, since activation orders always go out from the terminal LT, which functions as master. Both activation request and order are processed on the station side at a higher level than that of the line terminal. In detection of an activation request from the line terminal, a station EX sends an activation order via such terminal. Since the station EX is not part of the inventive subject, it is not described here but is only mentioned for clarifying the inventive concept.
The subscriber terminals ST are normally powered from the network terminal NT. Certain more complex terminals, e.g. display screens, are provided with their own powe
REFERENCES:
patent: 4143246 (1979-03-01), Smith
patent: 4314109 (1982-02-01), Sokiguchi et al.
patent: 4355386 (1982-10-01), Binz et al.
Olms Douglas W.
Scutch III Frank M.
Telefonaktiebolaget LM Ericsson
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