NO853984L - DATA TRANSMISSION CONNECTOR. - Google Patents

Description

The present invention relates to a coupling device for controlling data transmission, the device being arranged between a unit that sends out and/or receives data, e.g. a calculator or terminal, and a modem which can be connected to a data transmission line, or is combined with the modem, comprising a data buffer, a program store, a microprocessor and a timer.

With the intention of deploying terminals on a larger scale that do not themselves rely on any protocol for error recognition and error correction, in connection with applications where such error handling is unavoidable, there is a need for an interface which, on the one hand, enables a transmission via a telephone dialer line, and on the other hand, this makes the transmission error-free, as errors that occur are automatically corrected when the transmission is repeated. In and of itself, a transmission on select wires is only possible under the assumption of error-free, and in compliance with special conventions. In the case of an earlier proposal for the processing of procedure-free asynchronous terminals in half-duplex processes, convenience refusals still had to be made. However, it was desired to retain the response and full duplex characteristics of the terminal. Then a particularly simple and computer-independent data protection and compression can be carried out, and the transfer protocol thus even became a physically separate layer.

With such a plan, it must be established that there are definitely terminals that work with error correction, and that can be connected to the selector cables, but these devices are in principle manufacturer-specified. For these reasons, the criterion of manufacturer independence was put in the foreground.

In addition to this argument stated above, there are a number of further reasons which justify the introduction of asynchronous devices without a protocol.

a) Asynchronous devices with otherwise identical (possibly even better) properties are available for a significantly lower price than is necessary for the acquisition of protocol-supporting devices.

b) There is no manufacturer-independent protocol, and thus also no manufacturer-independent possibility to

connect terminals.

Thus, the decision for a protocol-oriented terminal already constitutes a certain fixation on the manufacturer and respective manufacturer groups in the future. It also makes a possible change of manufacturer unfairly difficult. c) Cooperation between different institutions is only possible by using well-defined intersection points. For the reasons stated above, plain software (transfer software) is often the only one possible for the asynchronous teleprinter interface. Examples include various information services that do not come via this central point. d) Asynchronous devices enable the transfer of single characters, while protocol-oriented devices usually work with a block structure.

With these considerations as a starting point, the invention aims to provide a switching device of the kind indicated at the outset, which under the additional condition of the fastest possible response speed - by which is also understood the possibility with which an entered character travels to the processing element - also allows a " block-secured" transmission also with respect to individual characters. The switching device must be able to be connected via telephone lines, which on the one hand means in dialer line operation, and on the other hand taking into account the corresponding answer and hang-up times.

With this guidance concept, the following aspects must be satisfactorily covered:

a) The sway delay must be as small as possible. The term response delay in the transmission is to be understood as the time from when it appears in the transmission link until it disappears from the transmission link. b) Possibility of transmission in both directions at the same time. The transfer link must at least be "recordable",

while it is just receiving data.

c) Independent transmission facilities on the link and at the ends. Selectable synchronous and asynchronous transmission on the link.

d) The general costs for control must be low.

e) The general costs for the synchronization shall be

low.

f) Character- or block-oriented transmission must be possible without further "transmit" - function control of

the user.

g) Possibilities for operation on selector cables.

These deliberations led to a completely separated from the rest of the processing over a guide link with two connecting devices arranged at the ends of the guide link, the invention consisting in the fact that for the connection of the unit that transmits and/or receives data, a serial standard cut point is arranged and when using a separate modem for the connection of the same, likewise a serial standard interface point, as well as an asynchronous transmitter/receiver for connecting the serial standard interface point or points with the data bus in the microprocessor, that the microprocessor controls a character or a block-oriented transmission with the introduction of one synchronization bit each, as the addressing in the data buffer on the sender side and the receiver side runs synchronously and there is an indication of how much of a received message is known, an ACK/NACK character is transmitted, and that the microprocessor further after a number of K of characters to be transmitted sends a block sample character BCC, and there as the characters to be sent are contained in the buffer storage, the transmission causes up to K characters, and if no correct message is ultimately received and the previous character was a block test character, the transmission ends.

One can think of a multipoint configuration as an extension, but this contradicts the condition (g) operability on selector cables. In order to satisfy the conditions (a) with respect to minimization of the response delay and (e) character-oriented transmission, the communication is character-oriented. However, it can be switched to block orientation if there is a corresponding data intensity. In this connection, the block length is defined as instantaneous in relation to the amount of characters present in the transmission. It is, according to the above, limited by a storage capacity for the transmission link, because, in the case of retransmission, the data must be available in the switching device.

The storage capacity for the data buffer in the switching device is e.g. 12 8 characters for the input, and 12 8 characters for the output. In the logically - not in reality - separated storage modules, an address can thus be addressed with one byte. However, only relevant characters are stored at all times, and no control characters.

Block sample characters are mixed in depending on data input, but at least all K characters. K is in this connection a configurable quantity, which will depend on the actual transmission speed. Typical sizes of K can be extracted from block sizes in conventional protocols.

The resulting response delay can therefore be expressed as:

Here, S is the time for the synchronization and Z is the number of immediately following characters. The number 2 consists of a character ACK/NACK and a block test character BCC. This delay is thus minimal in the event that individual characters are transmitted. The statement applies to the case that there is no data for transfer in the exact opposite direction. This will correspond to increasing the delay.

In order to keep the synchronization time S small, and to be able to transmit both synchronously and asynchronously on the link, a one-bit synchronization was chosen. A new synchronization is not necessary in connection with a synchronous transmission case, because this takes place automatically through the modem.

In the case of asynchronous transmission on the link, a single synchronization bit for a total block was also considered sufficient, because for the rate on both sides the control quartz in the microprocessor that operates the link is used, while at the same time it is possible to have an almost exact guarantee with the switching edge of the start bit at a cycle time for the processor of approx. 1.6 (as as well as used over feeding rates of 1200 repsective 2400 Bd.

The invention will be described in more detail below with reference to the drawing. Fig. 1 shows the most essential parts of the coupling device according to the invention without cut points. Fig. 2 is an example of the used cut points in the case of a synchronous mode stretch. Fig. 3 is an example of a signal transmission. Fig. 4 is a block diagram for producing the protocol processing according to the state of the art. Fig. 5 shows the inventive displacement of the transmission protocol from the computer or end device in the modem section. Fig. 6 shows the incorporation of the transmission protocol in the modem. Fig. 7 shows the addition of the transmission protocol as an additional device to the modem, and Fig. 8 shows a compilation of text-

blocks by different forms of transfer.

In fig. 1, the most essential parts of the coupling device according to the invention are made visible without cut points, and fig. 2 show them in connection with the own

equal control unit 1 used cut points 2, 3 on the asynchronous (transparent) side and on the side of the remote transmission, respectively. In this figure, the case of a synchronous modem line has been chosen as an example.

For the compilation of the information to be transferred, there are the following regulations:

i) Synchronization

ii) ACK/NACK character

iii) In the event that no correct message was received in the end

(v)

iv) In case of characters in transmitter buffer: transfer until

K character

v) in case preceding character BCC * > end Vi) BCC block test character

vii) > (iii)

Such a message is principally sent in response to a false or correct message. Since correct messages are only answered with real data, this cannot lead to conflicts. Thus, any message is considered "correct", which was correct at least until the first BCC.

The character ACK/NACK indicates how much of what was received was confirmed. In this connection, the addressing in the data buffer in the transmitter and in the data buffer in the receiver runs synchronously. The character ACK/NACK then constitutes the cyclic address of the last correctly received character. Thus, this character also takes over the ENQ function at the same time. There is even the possibility of a partial confirmation.

To prevent the transmission from stalling, respectively for

to start it at all, at one station it was

arranged a "timeout" activity. This means that when there is no activity on the line, this "timeou<f->activity sends out a block. In addition, the module on the terminal side is drawn in, so that the division of the connection by means of the modem in selector line operation is ensured on the computing side. Fig 3 shows an example of a transfer with a concept.

The one in fig. 4 schematically produced protocol processing according to the state of the art, is, in consideration of the transmission path modem-line-modem, connected behind the corresponding HW interface at all times. Such intersections are usually of the V 24 type. From the host's side, this protocol processing is connected to the intelligent element which is located at the far end. This is then either a calculator or the host itself. In all cases, the fulfillment of the transfer convention, the error recognition and the reaction to flawless transfer is a software issue. In this respect, one can also see a reason why all manufacturers only support "small" protocols from the front or main computer side, because otherwise the scope of software increases violently.

On the terminal side, the routing logic is mostly tied to the hardware in the terminal. Thus, the creation of several protocols at this location would not only involve the consumption of time, but also a change of the apparatus.

By means of the invention, the fulfillment of the transfer convention is fulfilled on both sides.

In addition, the requirements for the terminal and calculator must be kept to a minimum level. They were chosen as a pure character transfer (without further control) at a synchronous serial intersection site (V24). All additional intelligence and transmission control were logically incorporated into the modem line (see also Fig. 5): Calculator 4 (host or FE), series interface V24, control unit 1, modem 5, transmission line 6, modem 5,

control unit 1, serial intersection point V24, end device 7.

This incorporation of the coupling device according to the invention in the modem-line-modem section can in principle occur in two ways:

a) Installation in the modem (fig. 6) .

Thereby, the signals that have already been processed can be used

internal to the modem. Moreover, it is not necessary to make any adaptation of the signal level by means of suitable switching circuits. b) Incorporation as an additional device to the modem (fig. 7).

With this solution, the modem remains unchanged. Except

the above-mentioned aspects must also be taken into account that you also get an outlay for line connections, a cover and any necessary power supply. From a functional point of view, both variants are similar.

There is the possibility of laying out the transfer control from the complex central computer or from the end device, because the costs for a programmable control unit that can take over these functions are very low. Thus, the pure hardware costs for connection type (a) will amount to approx. DM 200 if the unit price is used as a basis. Individually, the hardware consists of

- Microprocessor

- PROM 512 x 8

- 2 x (256 x 8) RAM (realized as 1024 x 4)

- Asynchronous cut site

For further elucidation of the invention, a comparison will be considered with regard to a point-to-point prototype

check of the usual type, and a comparison regarding unsecured asynchronous transmission. Both comparison cases will be discussed because through the invention one can

Binary the characteristics that are considered positive in the two transfer types. With regard to the "effect terms", two aspects are to be understood: a) Throughput (=characters/time) in the case of continuous data supply. b) Propagation delay for a single respectively slowly typed character.

Figure 8 shows the three compared transfers

in its data transfer blocks.

The throughput in case I (asynchronous transfer) can be easily determined. Disregarding the necessity to mix in control characters for the transmission direction control, a maximum of N/e characters can be transmitted in N bit times, with e being 1 + k + s, where k is the number of bits including parity bit per data character, s constitutes the stop bit and 1 represents the start bit. If there are no restrictions on connectable devices, then s is chosen as two.■ At a transmission speed of 2400 bits/s, this gives a transmission of 13,091 data characters/min.

In cases II and III, in addition to the transfer time, the switching time for the change of direction must also be calculated - twice per block - in addition to the pure transfer time. Thus, in case II, on the assumption that a confirmation consists of ACK ETX BCC, an outlay per block (= b character) on:

i) Two modem connection times 20 - 200 ms

ii) Twice synchronization for every 2-4 characters =4-8

sync sign.

iii) 6 control and block sample characters

iv) b data characters.

Under the assumption of 2400 bits/s during a connection time of 100 ms, as well as 3 sync characters per transmission and a typical data character count of 50 characters, you get 7377 data characters/min. The comparison with the asynchronous transmission can only be found at a block length of approx. 200 characters/block. Protocols with a "polling" structure and a "multidrop" structure, respectively, provide significantly less favorable throughput figures. Furthermore, it is not immediately possible to increase the number of characters/block arbitrarily, because this will result in an increase in the re-transmission frequency and thereby a reduction in throughput. In addition, call delays must also be taken into account, because a continuous "empty transmission" is not correct when operating using the calculator or using a front-end calculator.

Case III, unlike II, includes a 1-bit sync character and an 8-bit ACK/NACK character, as well as a BCC per partial block. At 50 characters/subblock, this gives a throughput of 14,139 characters/min. This is achieved because several partial blocks are transferred one after the other in one direction.

With a partial block length of 10 characters, you get an additional throughput of 13 30 3 characters/min. On the other hand, through the sub-block confirmation, in the event of an error, due to the additional buffer element "transfer unit", no further compensation is obtained either.

The point "propagation delay" is in case I clearly a length of time, i.e. in the situation "wire free" 10 5 ms, since the switching delay is taken into account. Case II

is difficult to categorize because recognition of "single characters" is usually not possible. Such devices mostly have a "transmit" key to avoid the conflict and situation on the inside, and only have blocks that are inefficient and more difficult to process from the front end. On such devices, the keyboard is also "blocked" significantly more often, usually during each input transfer until confirmation.

In case III, the transmission delay of a single or slowly entered character means the delay caused by the transmission of a 1-character block. It amounts to 217 ms. If the input speed or the data input speed becomes higher, then sub-blocks are first combined until finally several characters are combined in a sub-block. In this connection, the average delay time does not change significantly, but the maximum delay time for a character at full load can rise to approx. 850 ms. A blocking of the keyboard or a non-recording of the report only occurs in the event of an error, when the capacity of the data buffer in the transmission unit is no longer sufficient.

By using highly integrated building elements, it is possible with minimal costs to avoid the problem of manufacturer dependence as regards the terminal sector, and to adapt to forms of transmission, which on modem transmission lines retain the characteristics of directly connected devices. This transmission method is indeed, when it is tuned to the asynchronous cut point, character-oriented, but is otherwise completely transparent, i.e. there are no characters that disturb the transmission structure, or are absorbed by it.

Claims (1)

Connection device (1) for control of data transfer, in that the device is arranged between a unit that transmits and/or receives data, e.g. a calculator (4) or an end device (7), and a modem which can be connected to a data transmission line (6), or is combined with the modem (5), comprising a data buffer, a program store, a microprocessor and a timer, characterized in that for the connection of the unit that transmits and/or receives data, a serial standard interface point (V24) is arranged and, when using a special modem (5) for connecting the same, a serial standard interface point (V2 4) is also arranged , as well as where an asynchronous transmitter/receiver is arranged for the connection of the serial standard interface point or points with the data bus in the microprocessor, that the microprocessor, depending on the data supply, controls a character- or a block-oriented transfer with the introduction of one and one synchronization bit, as the addressing in the data buffer arranged on the sender side and arranged on the receiver side run synchronously, and that to indicate how much of a received message has been confirmed, an ACK/NACK character is entered above, and that moreover, after a number K of characters to be transmitted, the microprocessor sends a block test character BCC if the characters to be sent can be accommodated by the buffer storage, causing transmission of up to K characters, as well as, in case no correct message was finally received, and the previous character was a block character, causes termination of the transmission.