Patent GB-1326569-A (GB)
Title: Systems for information exchange
IPC: H04J3/08
Filed: 1970-09-03
Abstract: 1326569 Digital transmission; party line systems ADAPTIVE TECHNOLOGY Inc 3 Sept 1970 [29 Sept 1969] 42232/70 Heading H4P In a method of transferring messages between stations permanently connected to a network, transmission time is divided into equal time periods divided into sub-periods some of which may be utilized for identification purposes. The stations operate in synchronism to identify the repetitive periods P which are divided into sub-periods SIP. Some periods P may be used for preliminary control purposes and each sub-period SIP has a specified designation, e.g. letter, numbers &c. also an address and and identifying signals. Not all stations need to to have the same assigned designations. In a basic arrangement, if the first SIP represents letter "A", a station identifying signal placed in this SIP will cause that station to record an "A". In the embodiment described, P = 134 SIP's and certain SIP's are allocated to prescribed characters, e.g. an alphabetical letter, but as certain letters, e.g. "E" are used in English language more than say "Z" this will mean in each period that a number of SIP's may not be utilized. A particular feature of the arrangement is that any character may be dropped into the first "free" sub-period and a signal 15 sent to the receiver which instructs it that the character has been displaced so that the receiver converts the character back to its original form. For example an "E" normally allocated to SIP 5 may be dropped into any free SIP, say SIP 26=Z and the signal is sent to the receiver so that it reads out an E and not a Z. The transfer signals are sent in a determined period designated HSI (see Fig. 1, not shown). Such technique is termed "Z numbers" in the Specification and this may be arranged either to a determined pattern or in a random coding technique "scrambling" which is not easy to decode and lastly prevents unauthorized reception. This technique avoids a situation that with numerous stations competing for a particular SIP, a station may have to wait several periods before the particular one is free. Each SIP contains a number of bits, e.g. 8 and the system operates by sending in each effective SIP the station identification code of the receptor station (S) i.e. if a H is required to be sent to a particular station then in SIP = 8, the identification signal SI of the receiver station is inserted which is recognized by the appropriate receiver and for the relevant SIP hence if the receiver is a teleprinter it prints H. An originator station selector (8), Fig. 8 (not shown), ensures non-simultaneous transmission in any SIP such selector being described as a motor driven rotary switch or equivalent electronic circuit. The system may operate on a two-way basis. Each station may also act as a repeater in a serially connected system (Fig. 10, not shown) and a central station co-operating with a number of peripheral units may also be provided. "Z numbers".-To restore the original character which has been moved to another SIP, the originating station adds a Z number. On reception of the Z number this moves the character to its proper position and produces the complement which is returned to the sending station where it is added to the original Z number producing a total of "all ones" thus checking that the process has been completed correctly. In this process the "carry" is ignored. In the Z circuit (64), Fig. 12 (not shown), with an original number of 5 (101) then if say 3 (011) is added, neglecting carry, the total will be 110. At the receiver 011 is added to 110 to produce the original signal 101. Other types of number may be used as follows: S numbers to identify particular facilities i.e. files; N numbers to identify particular machines, e.g. a teleprinter or data processor; P numbers to identify customers, e.g. those having a high degree of priority. As described the system receives ternary data which is transmitted as duo binary for reconversion to ternary at the distant end.