Communications: electrical – Continuously variable indicating – With meter reading
Patent
1982-12-15
1986-11-18
Yusko, Donald J.
Communications: electrical
Continuously variable indicating
With meter reading
370 86, H04Q 900, H04J 308
Patent
active
046238859
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a method and arrangement to distribute send permission to any of the terminals in a telecommunication network when transmitting information between terminals which are inter connected through a common ring bus and controlled by a computer located in each of the terminals.
BACKGROUND ART
An arrangement for the distribution of send or write permission to computers connected in a loop is described in an article by M. T. Liu and C. C. Reames, "The design of distributed computer network", Proc. Int. Computer Symp. 1975, Vol 1 pages 273-282. The article shows that by permitting a computer to send, i.e. to break the loop, on condition that no information frame is passing that moment, several terminals can send at the same time. Each computer is then prepared to receive incoming data, store the data in a buffer store and to return the data to the loop (Ref 1).
Another known device gives send permission by means of a special bit pattern. The bit pattern is converted or reshaped (retransmitted) depending on whether the send permission is accepted or refused. The device is presented in an article by W. D. Farmer and E. F. Newhall, Proc, ACM Symp. Probl. Optim. Data communication System 1-33, 1969 (Ref 2).
SUMMARY OF THE INVENTION
As has been shown above there are several different ways to administer the sending of data between computers connected to a ring bus. The problem with the arrangement according to Ref 1 is that it due to its complexity it also demands a complicated hardware.
The arrangement shown in Ref 2 results in a bad security in the transmission, since disturbances easily can give rise to send permission because the bit pattern is unguarded as it is not part of a standardized HDLC-frame (no FCS).
The arrangement according to the invention, which is characterized in accordance with the claims, solves such problem by having a send permission frame, (so called token frame) of HDLC-format (High Level Data Link Control) containing a send permission constituting a determined signal pattern, circulate on the ring bus. When a determined logic condition appears in any of the connected terminals indicating that the terminal wishes to send on the bus, send permission is given to that terminal which due to the position of the frame on the loop first occupies such determined condition by detecting the token frame in such first terminal. This terminal then places an abortion pattern in the token frame which is sent to the bus. Thus the contents of the frame will be invalid and distribution of the send permission to any of the other terminals impossible, as only one terminal at a time may send on the loop. The described process means that the token frame is received and aborted towards the bus if the terminal wishes to send, but is aborted towards the terminal and looped through the terminal if this terminal does not want to send.
BRIEF DESCRIPTION OF DRAWINGS
The arrangement according to the invention will be more fully described below by means of an embodiment with reference to the accompanying drawing in which
FIGS. 1a-d schematically show a process in accordance with the arrangement according to the invention with a number of terminals connected to a common ring bus,
FIG. 2 is a block diagram of the arrangement in a terminal according to the invention,
FIG. 3 is a block diagram of a flag detecting circuit FL which is part of the arrangement, and
FIG. 4 is a block diagram of an address comparison logic AL which is part of the arrangement.
PREFERRED EMBODIMENT
As shown in FIG. 1 four terminals TR1-TR4 are connected to a common serial ring bus RB. It is assumed that the terminal TR2 wants to send a message to the terminal TR4. A send permission frame (token frame) SP having a HDLC-format is circulating on the bus. As the terminal TR2 wants to send and thus needs a send permission, the send permission frame is received by the receiving part R of the terminal TR2. When the receiver recognizes the bit pattern of the token frame it knows that it has send permission an
REFERENCES:
patent: 3593290 (1971-07-01), Kerr
patent: 3985962 (1976-10-01), Jones et al.
patent: 4387425 (1983-06-01), El-Gohary
patent: 4393497 (1983-07-01), Cantwell, Jr.
patent: 4410985 (1983-10-01), Yasumoto et al.
Bladh Eric A.
Lindholm Lars .ANG.ke A.
Telefonaktiebolaget LM Ericsson
Yusko Donald J.
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