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.N:78 .H:=========================================================================== .H:BOOK 1 ...FUTURE SYSTEMS by Mark T. Nadir... PAGE $$$ .H:=========================================================================== .H: .H: .R: CHAPTER SIX IN A NUTS HELL PROCEDEURE 1 Positional Transduction Methodology is not one system but an entire class of systems. Each individual class of systems is, in turn, com rised of a number of Modes. These can be thought of thusly: [1] each class as a particular basic program comprised of many separate Modes while [2] each Mode can be thought of as separate subprogram. 2 The simplest conceivable Positional Transduction Methodology system is a 100% artificial system created for the exclusive purpose of in troducing you to PTM technology. This system is called the "Two-Sub scriber SysTem". The only reason for its existance is to introduce you to PTM technology. 3 The Two-Subscriber SysTem is not a fully developed PTM system. Many of the features of true (i.e. operative) PTM are lacking and will have to be presented to you later. Never-the-less the basics of Posi tional Transduction Methodology are present. 4 There are three aspects of the two-Subscriber SysTem that will have to be dealt with (with are not always separated). They are:- [1] A simplified description of the Two-Subscriber SysTem, [2] some back ground notes (which might seem irrelevent to you), and [3] a more detailed description of several of the basic of the Two-Subscriber SysTem components. These last, might be either softwarelike or hard ware components. The first of these [1] will be the subject of this chapter. The other two will be reviewed in the next chapter. 5 [1] The Two-Subscriber system will first be described with sketchy details. The purpose here is to present an overall outline which can be reasonably easy to visualize. This will give you an overall view of this system. Many of the details will be filled in later in the next chapter. 6 [2] The function of the background material (which is included below) is to give those who are not systems specialists to be able to com pare what is being offered herein to what is being done in the field. That is to set up standards of comparison. That information is to be found in chapter 7. 7 [3] There is material which describes in much greater detail just how some important functions are performed. This material is offered not only to fill in the outline of the sketch but to also provide a basis for understanding other systems which are to follow (in chapters 8 to 13 in this book). Some of this material is software-like and some of it is hardware-like. That too, appears in chapter 7. THE TWO-SUBSCRIBER SYSTEM 8 The main features of the Two-Subscriber SysTem will be described in this section (e.g. under the heading Two-Subscriber System). 9 The Two-Subscriber SysTem is shown in the block diagram of figure 1. The Two-Subscriber SysTem itself consists of the two uniplexers A and B plus the two transmission paths labeled "Path 1" and "Path 1". The subscibers' terminal equipments are regarded as external to the Two Subscriber SysTem. The subscriber, in this diagram, is able to enter the SysTem through his or her terminal equipment. 10 The subsciber's terminal equipment is herein defined as devices such as tele-typewriters, computer terminals, telephones, facsimile (fax) machines, and such like equipments. All terminal equipments generate signals and that is the characteristic they share in common. Terminal equipments come in two varieties: - analogue and digital. Tele-type writers, computer terminals, etc. are digital. Telephones are analog. Fax machines might be either. 11 All digital terminal equipments, in response to the operators inputs, generate CODES. These same machines can also receive CODE and in response to the code input generate (print) characters, e.g. letters, numbers, punctuation, etc. The Two-Subscriber SysTem works only with inputs from digital terminal equipments. These terminal equipments also accept and respond to code supplied from the Two-Subscriber Sys tem. 12 Signals generated by analogue equipments can be converted to a digit al form by analogue to digital (A to D) converters. This idigitized data can be re-converted to analogue form by digital to analogue (D to A) converters. This function is normally performed in actual sys tems by the uniplexers but for now it will assumed to be performed by A to D and D to A converters. 13 The terminal equipments feed data to the uniplexers for transmission to the only other subscriber in the SysTem. The uniplexers, in turn, feed data to the terminal equipments after it has been received from the other subscriber. Therefore, the input and output of the uniplex er is data in the form of code. 14 The terminals of the uniplexer which receive data from and which in turn drive the subscibers' terminal equipments are called the extern al terminals, i.e. they are sources of and sinks for external data. (The terminal equipments are external to the system, as noted above.) 15 The uniplexers have another set of terminals. They are the internal or system terminals to which paths 1 and 2 are connected. The inform ation which flows over these transmission paths is "PTM Language". PTM does not convey code. And codes never appear on any Positional Transduction Mothodolgy transmission path. 16 PTM Language is a implicit language! That is to say that it never appears upon on the transmission path.(It is never explicit.) The on ly things that ever appear on the transmission paths are Tags. In the Two-Subscriber System only one type of Tag is employed. That Tag is called the Address Tag or simply the Address. The size, in bits, of the Address Tag is determined by the number of subscribers to the system. The Two-Subscriber System has an Address (Tag) which is one bit long. 17 Uniplexer are the only hardware found in any Positional Transduction Methodology System. In fact, it is one of the two types of components that comprise all Positional Transduction Methodology SysTems. There are just these two types of components and nothing else. 18 The uniplexer is a hardware device which provides a number of funct ions. We have encountered four such functions so far. They are [1] accepting data for transmission from the subscriber's termnial equip ments, [2] delivering data, in the form of code, to the Subscriber's termnial equipment, [3] generating PTM Language, and [4] (by implication) receiving PTM Language from the other uniplexer. 19 What actually occurs is that the uniplexer receives data, in the form of code, from its subscriber's terminial equipment and converts it into PTM Language. This PTM Language is put on the transmission path and sent (actually transferred) to the other uniplexer. The other uniplexer receives the PTM Language and converts it into code which it then sent to its subscriber's termnial equipment. There are, two conversions therefore. [1] Once from code into PTM Language and [2] a re-conversion from PTM Language into code. 20 A PTM Language is any of a large number of digital languages employed by the various PTM Modes. In order to make sure that data is correct ly received, all digital languages (and code) transmit and receive a "sync signal". Positional Transduction Methodology systems are no exception to this rule. The Positional Transduction Methodology sync signal is called the MARKER. This, then, is another function which the uniplexer performs: it generates and receives the Marker. 21 In order to perform the above function correctly the uniplexer must be equiped with circuits that generate (and measure) timing signals. This is discussed in considerable detail in a later chapter. 22 There are many PTM Languages. The Two-Subscriber System will employ only one PTM Language to keep things as simple as possible. 23 Data is sent in ForMats. A ForMat is the interval between two Mark ers. Just that, nothing more. ForMats can be subdivided into sections and subscetions. The ForMat employed by the Two-Subscriber System has only one section. In the Two-Subscriber System that section is called the Address Section. 24 The first Marker is assigned to the ForMat and always comprises the first nest therein. The next Marker, consequently is part of the For Mat which follows. 25 All sections are divided into nests. A nest is some number of bits long. Except in Two-Subscriber Systems where the nests are one bit long. All nests in a section are contiguous. The Data that goes into a nest is called an Address. The Address, in Two-Subscriber Systems, (as may be deduced from the above) is exactly one bit long. (The size of a nest and the size of the data (both measured in bits) must always be identical.) In our case both a nest and a bit is one bit long. (The one bit nest is an exception in Positional Transduction Methodology SysTems.) 26 A one bit long Address will suffice in Two-Subscriber Systems because the bit always represent the address of the OTHER subscriber. With only two subscribers no confusion results. 27 The address is part of the PTM Language employed to transfer informa tion between subscribers. It is the explicit "notifier" for the lang uage. But, the language itself is implicit, as noted earlier. The ad dress identifies the receptor in all Positional Transduction Method ology SysTems. In the Two-Subscriber System identification of the re ceptor is no problem; it is simply the other subscriber. Consequently one bit will suffice. 28 The Address serves to notify the receptor that the nest bearing the address contains (implicit) data for the named receptor. It does not state what the data is or imply any quality relating to or of the data. 29 The fundament theorum of Positional Transduction Methodology can now be evoked: "The position an item has with respect to a Marker can, or can be made to, contain information." This is the basis for PTM Language. The ForMat contains the Marker (as was stated in paragraph 24). Each nest has a position with respect to the marker. Each nest must have a sequential position with respect to the Marker because the digital data stream is sequential and because one nest follows the other. 30 [Warning The nest in the Two-Subscriber System is one bit long. But, the bit must not confused with the nest. The nest in future systems is very rarely one bit long. It is generally several bits long. In large systems an Address Nest might be greater than twenty or even forty bits long.] 31 The location of a nest with respect to the Marker can be, and is, de termined by a counter. This counter is started when the Marker is de tected; it is then stopped and restarted by the next Marker. The out put of this counter, therefore states explicitly the sequential loca tion of each and every nest in the ForMat. This counter is part of the hardware in every uniplexer. 32 Each uniplexer also contains a device which acts as a Look-Up Table. In theTwo-Subscriber System each nest position represents a charact er or a punctuation mark. The character is determined by the Look-Up Table. A section of a Look-Up Table is shown below. .- ╔══════════════════════════════════════════╗ ║ NUMBER CHARACTER ║ ║ (FROM COUNTER) (REPRESENTED NY NEST) ║ ║ ║ ║ 1 A ║ ║ 2 B ║ ║ 3 C ║ ║ 4 D ║ ║ 5 E ║ ║ 6 F ║ ║ 7 G ║ ║ 8 H ║ ║ ║ ║ AND SO ON. ║ ║ ║ ║ TABLE A. ║ ║ PART OF A LOOK-UP TABLE ║ ╚══════════════════════════════════════════╝ .+ 33 When we examine the above Look-Up Table we see that the first nest re presents "A", the second nest "B", the third nest "C", the forth nest "D", and so on. These then are the implicit characters that each nest REPRESNTS. 34 THE ABOVE IS THE FUNDAMENTAL METHOD WHEREBY A CHARACTER IS ASSIGNED TO EACH AND EVERY NEST IN THE FORMAT. IN ALL SYSTEMS THE LOOK-UP TABLE IS ALWAYS THE DEVICE THAT ASSIGNS A CHARACTER, SYMBOL, PUNCTUA TION MARK, NUMBER, ETC. THEREFORE, THE DEVICE WHICH ACTS AS THE LOOK UP TABLE FOR THE UNIPLEXER IS ALSO THE DEVICE THAT ASSIGNS CHARACTERS TO THE NESTS. 35 PTM Language is comprised of two parts. An explicit part (which is called the Address) that notifies, the receiving uniplexer, that a character (or any item) is in that nest. And, furthermore, that char acter (or other item) is for the uniplexer whose address in in that nest. The address consequently, performs two distinct function: [1] notify the uniplexer that the marked nest contains data and [2] specifies who that receptor shall be. 36 The two foregoing distinctions are trivial in Two-Subscriber Systems. However, these distinctions are very important in all the Positional Transduction Methodology systems described later. For this reason the distinction must be very clear in your mind. 37 The implicit part of PTM Language is the location assigned to each character by the Look-Up Table (or its equivalent). 38 To send a message in the PTM Language of the Two-Subscriber System a "one" is entered into each nest that represents the next character which is to be TRANSFERRED from one subscriber to the other subscriber. Both the originating uniplexer and receiving uniplexer require the Look-Up Table in order to transfer data. 39 In Table A above, under the heading "CHARACTER (REPRESENTED BY NEST" we have letters. But the uniplexer does not receive letters from the subscriber's terminal equipments; it does receive codes which do re present those characters. Therefore, the Look-Up table has code char acters in that column rather than letters. Now, the uniplexer can compare the code received from the local subscriber's terminal equip ment directly with the code in the Look-Up Table and select the cor rect nests to enter. The mechanism is described in considerable de tail later on. 40 The same Look-Up Table is employed in the receiving uniplexer. When a marked nest is detected the number of that nest is specified by the counter. That number is fed to the Look-Up Table mechanism which loc ates a code character in that table having THAT number. That code character is then sent the the receiving subscriber's terminal equip ment where it is printed out. This mechanism is also described in detail later on. 41 The uniplexer, therefore, when "transmitting" converts code into PTM Language, and when receiving, it can converts PTM Language into code. Therefore, the only data actually transmitted are addresses. The data is transferred. 42 The particular PTM Language shown and discussed above is (or can be) unique to Two-Subscriber Systems. However, the same basic approach is employed by all Positional Transduction Methodology Systems. There are many variants, each expressed as a distinct Mode. We will be in troduced to them, in due course. 43 PTM Language will be illustrated in the following chapter. 44 The consequences of employing PTM Languages will be seen to be very far reaching. This will at taken up in the correct time. The reader might be able to foresee some of the consequences now. 45 The PTM Language chosen to illustrate the operation of the Two-Sub scriber System is very inefficient by code standards. Let us see just how "efficient" THIS PTM Language is. The "efficiency" will be mea sured in terms of the number of bits required to transfer one stat istical character. 46 To determine how many (code) characters are transferred in a ForMat (which we must know on order to determine the above "efficiency"). To do this we will need to review some additional material which has not been spoken of previously. One of these is a parameter called herein the "PROBABILITY OF ENTRY" (or P of E). The other is the "CHARACTER-SET" employed. We will start with the latter. 47 The character-set is any group of characters each of which is unique. The set can have as many or as few characters as desired. Through the years subscriber terminal equipments have evolved character-sets many of which have become standard. These character-sets almost always contain [2n] characters where n usually varies between 4 and 8. PTM systems are constrained by standards which are set up for code sys tems because of the subscriber's terminal equipments. 48 Because of the way Positional Transduction Methodology SysTems work, the number of Addresses (representing characters) entered into a character-set is not a fixed quantity. This number cannot be deter mined before hand. The best that can be done is to determine a number statistically. The number provided by statistics is called the PROB ABILITY OF ENTRY or simply the P of E. The P of E is stated as the number of statistical times a subscriber can enter an address (and therefore a character) into a character-set. 49 The P of E will vary with conditions. This matter is discussed furth er in later chapters of this book. For the Two-Subscriber SysTem the P of E is 2, i.e. two statistical characters can be expected to enter be entered into each character-set. 50 Now, we are in a position to determine the "efficiency" of PTM Lang uage as employed by the Two-Subscriber SysTem. The character-set chosen will assumed to be the bidaut character-set which is comprised of 32 characters. Because of use of PTM Language, a character is sent by entering a single address bit into a nest. The P of E tells us that two characters can be expected to be entered in a character-set which is 32 bits (characters) long. Therefore, each character requir es [32/2 = 16] bits (counting all the bits in the set, both used and unused). The "efficiency" is poor. This characteristic of the Two- Subscriber SysTem but, not of Positional Transduction Methodology Systems. 51 The Probability of Entry given above (as 2) might seem very low. But, most Positional Transduction Methodology Systems are Mass-Access Sys Tems and a P of E of 2 can actually be too large. 52 Mechanisms which provide Probabilities of Entries much higher than 2 are known (to the Author). 53 The foregoing should give the reader a clear but not excessively de tailed picture of the operation of the Two-Subscriber SysTem. The em ployment of too much detail was carefully avoided in order to avoid "snowing" the reader under with detail. In the next chapter (chapter 7) more details will be found on both how the Two-Subscriber SysTem and other PTM systems operate.