Multiplex communications – Wide area network – Packet switching
Patent
1983-12-21
1985-11-12
Olms, Douglas W.
Multiplex communications
Wide area network
Packet switching
370 85, 3408255, H04J 600
Patent
active
045532354
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The invention relates to an apparatus for connecting digital terminals to a digital exchange via a terminal junction point.
BACKGROUND
In future digital communication systems including terminals for both data transmission and speech connections (Integrated Services Digital Network, ISDN) the subscribers will be connected to digital exchanges via digital subscriber lines. Through a bus network or a star network, all the terminals will be in communication with a terminal junction point, which in turn is connected to the exchange.
Different solutions are conceivable for multiple access in a digital subscriber connection. One possibility is polling, for example, where the terminal junction point gives permission to the terminals to send in a given order. The method requires that each terminal has an unambigous individual address, which causes large practical problems however.
According to another solution, the terminal wanting to send data information investigates whether the data channel send direction is idle and the channel is then engaged, while if this is not the case there is a wait of one time interval before a new attempt to send is made. If several terminals start sending simultaneously, this is detected and sending is interrupted by all the terminals. Collision is usually detected by the signals on the transmission medium having an unexpected distortion. This method requires that each terminal has access to signal information from all the other terminals, which is a disadvantage.
The aforementioned solutions are described in the publication "Multiaccess Protocols in Packet Communication Systems", IEEE Trans. on Comm, Vol COM-28 NO 4 April 1980, Fouad A. Tobagi.
SUMMARY OF INVENTION
An object of the invention is to provide an apparatus which gives multiple access, with the aid of simple means, to a digital subscriber line, and enables the utilization of the same terminal interface for both bus and star structures.
In achieving the above and other objects of the invention, there is provided an apparatus in a digital communication system for connecting digital terminals to a terminal junction point which in turn is connected to a digital exchange, the apparatus being characterized in that the terminal junction point contains a directing means sending in a first state a flag signal to all terminals as well as to the exchange where the signal is utilized for filling out empty space in the information flow and in its second state sending an information packet received from a terminal towards the exchange as well as to all terminals. The terminals furthermore contain means for sending out an information packet in response to the flag signal having been received a given number of times. The reception of the information packet at the junction point resets the direction means to its second state. The terminal includes comparison means for determining whether the packet information sent back from the junction point corresponds to the terminal's own sent-out packet information. Furthermore, there is included means responsive to the comparison means disconnecting the terminal if the sent-out packet information is different from the sent-out packet information.
The above and other objects, features and advantages of the invention will be found in the detailed description which follows hereinafter.
BRIEF DESCRIPTION OF DRAWINGS
The invention will be described in detail below in the form of an embodiment illustrated in the accompanying drawing in which:
FIG. 1 illustrates a terminal junction point to which terminals are connected via a bus line or via lines connected in star pattern;
FIG. 2 shows the frame configuration for signalling from the terminals to the exchange; and in the opposite direction,
FIG. 3 illustrates a terminal junction point for co-operation with bus-connected terminals;
FIG. 4 illustrates a terminal and FIG. 5 illustrates a terminal junction point for co-operation with star-connected terminals.
DETAILED DESCRIPTION OF INVENTION
FIG. 1 schematically illustrates a d
REFERENCES:
patent: 4161779 (1979-07-01), Spencer et al.
patent: 4450554 (1984-05-01), Steensma et al.
patent: 4494113 (1985-01-01), Yamaoka et al.
Olms Douglas W.
Telefonaktiebolaget LM Ericsson
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