IMPROVEMENTS IN OR RELATING TO DATA TRANSMISSION SYSTEMS

Abstract: A monitoring apparatus for monitoring the access ports of a viewdata computer comprises a microprocessor 30 and associated RAM 31. Information indicative of the condition of the access ports is fed into the RAM 31 under the control of the microprocessor 30 via input/output latches 35 which are linked to the ports. An interface circuit 37 periodically assem­ bles a message relating to the condition of a port as indicated by the information stored in the RAM 31 for transmission to a monitoring centre where the information can be displayed on a conventional viewdata terminal.

Description: DESCRIPTION This invention relates to data transmission systems. The invention particularly relates to the monitoring of a data transmission system. In a data transmission system of the viewdata type information is stored in a computer based at a viewdata centre. The computer has a plurality of ports each of which is linked to the public telephone switched telephone network by an interface line and a modem. Users of the system can access the computer by way of the public switched telephone network using suitable terminal equipment such as a modified television set and a key pad for use in accessin the computer. The computer centre is generally unmanned and there is a requirement for a monitoring facility to enable remote monitoring of the computer access ports to be carried out. The present invention is concerned with an arrangement which can provide such a facility. According to the present invention there is provided apparatus for monitoring the access ports of an information store of a data transmission system comprising means for sequentially scanning the ports, means linked to said scanning means for storing information indicative of the condition of each port, and means responsive to data received from said storing means to generate a data signal or signals indicative of the condition of a port for transmission to a monitoring location. The apparatus may comprise a microprocessor which is arranged to scan a plurality of latches each of which is associated with one of said ports. The microprocessor may have an associated random access memory which stores data indicative of the condition of said ports and which is updated cyclically as the latches are scanned. When the data transmission system is a viewdata system the monitoring location can include a conventional viewdata terminal which is linked to said generating means and is arranged to display information relating to the condition of each port. The condition of each port may be represented by a geometric shape on a visual display unit, the colour of geometric shape being indicative of the condition of the associated port. The shapes may be displayed as a matrix of m by n characters. The invention will be described now by way of example only with particular reference to the accompanying drawings. In the drawings: Figure 1 is a plan schematic view illustrat ing the manner in which monitoring apparatus in accordance with the present invention is used in a viewdata system; Figure 2 is a block schematic diagram of a monitoring apparatus in accordance with the present invention; Figures 3 and 4 illustrate display layouts as used in the present apparatus, and Figures 5a to 5c, 6a to 6c and 7a to 7c are flowcharts illustrating a program for the microprocessor. Viewdata is a system for providing information. The system is based upon a cpmputer in which the information is stored. Users of the system can access the computer by way of the public switched telephone network using suitable terminal equipment. The terminal equipment includes a visual display unit, typically a modified television set, and a key pad for use in accessing the computer. The computer is located at a vnewdata centre which is illustrated schematically ir Figure 1 of the drawings. The computer is shown at 10 and has a plurality of access ports each of which is connected by a V24 interface cable 11 to a modem 12. Each modem 12 provides an interface between the cable 11 and a two-wire telephone line 14 which links the modem to a telephone exchange 15. When a customer dials the viewdata centre a telephone link is established to the computer via the exchange 15, one of the two wire lines 14, a modem 12 and an interface cable 11. The present description relates to a monitoring apparatus which can monitor the condition of each modem 12 and the associated cable interface 11. The monitoring apparatus is shown schematically at 20 and has an input 21 from each of the cables 11. The monitoring apparatus 20 has an output 22 which can be used to provide a signal to "busy" each of the mc ems, i.e. to take each of the modems out of operation. The apparatus also has other outputs which include an output 23 which leads via a private wire to a display unit for displaying information received by the apparatus 20 via inputs 21. This display unit can be similar to that used in a customer's terminal equipment. The monitoring apparatus 20 is shown schematically in more detail in Figure 2. The apparatus is based upon a Motorola M66sO0 Microprocessor 30. The microprocessor 30 has an associated 8K random access memory 31 and a 4 x 2 K programmable read only memory 32 both of which are linked to the microprocessor by a microprocessor bus 33 having 16 address, 8 data and an appropriate number of control lines. The apparatus 20 also has a plurality of 8 bit parallel input/output latches which are mounted on boards shown at 35. The boards 35 have 196 4bit inputs which are connected one to each of the viewdata modems 12. Each of the latches is associated with a pair of input ports, four of its bits representing the status of one port and the other four representing the status of the other port. The boards containing the latches are connected to the microprocessor bus 33. The apparatus also has a four channel serial input/output device comprising an MC6850 ACIA interface 37 which is linked to the microprocessor bus 33. The interface 37 provides a connection to a viewdata operations centre via a modem 38, to a local viewdata managers office via a modem 39, to a public switched telephone network access via a modem 40 and to a local site display indicated at 41. The output from the interface 37 is transmitted at 1200 bits/sec over a Datel 600 circuit with a full duplex return speed of 75 bits/sec. The microprocessor bus 33 also has a connection to a plurlity of boards 42 which comprise 196 Ibit busy control outputs each of which have a connection to one of the modems 12. The inputs to the circuits 35 are standard V28 levels. In order to render the levels suitable for the latches, the boards 35 include circuits for converting the levels. The port signals that are monitored via the input/output latches 35 are: 1) Modem on line, i.e. customer using the modem. 2) Received carrier detected from customer's modem. 3) Transmitted data detected. 4) Modem busied via monitoring equipment. The first three signals are derived directly from the normal computer/modem interface circuits. The fourth signal is derived from a contact of a relay in the control unit of each modem. The control programs for the apparatus are contained within the memory 32 which is non-volatile. In operation when the apparatus is switched on power is applied and all units are reset. The microprocessor 30 looks to the memory 32 for instructions and its first action is to set up the input/output interface circuit 37 to the correct condition. The next instruction results in the microprocessor clearing the random access memory 31. When the memory 31 has been cleared the microprocessor 30 begins scanning the latches on the boards 35. As the microprocessor scans the latches it feeds into locations in the memory 31 information indicative of the status of each of the 196 ports which are being monitored so that a status table indicative of the status of the ports is created. The ports are scanned cyclically, each scan taking approximately 50 milli seconds. Every 120th of a second the scanning is interrupted on receipt by the microprocessor of an interrupt signal from the circuit 37. Upon receipt of such an interrupt signal the microprocessor looks to a particular memory location in the RAM 31 and transfers the information from that location, which represents the status of a particular port, to the circuit 37 which assembles this information into a message for transmission on its four output lines. The microprocessor 30 then continues scanning the latches 35 until it receives the next interrupt signal when another memory location in the RAM 31 is addressed. It will be noted that the circuit 37 transmits characters to all four of its outputs at the rate of 120 characters per second, each character representing the status of a port. As a display unit has 960 characters in a frame block there is a refresh time of 8 seconds. The display is updated continuously during normal status display with a cursor "homey character after each 960 character frame block. The manner in which the information relating to the ports is displayed is shown in Figure 3. This figure represents a conventional viewdata display layout. It consists of an array of 960 characters in a 40 x 24 matrix. Each port is represented by a block 50, the colour illuminated in each block being indicative of the status of the port as monitored. The arrangement is such that the condition of up to 196 ports can be displayed. The status colours can be as follows: BLUE - not in use GREEN - free waiting for a call CYAN - call in progress YELLOW - modem on line MAGENTA - carrier detected RED - port busied out. During normal status display the frame is continuously written with the cursor "home" character after each frame of 960 characters. Facilities are provided for busying a particular port from a viewdata operations centre. This can be done by pressing an appropriate key which sends a signal via the output circuits 42 to the relevant port. When a busy command is received by the apparatus 20 from one of its control-port inputs the other control-port inputs are disabled for 30 seconds. Thus, such a command passes control of the unit to the first control-port input to send the command. The 30 second period is renewed on each subsequent character received from the active control-port input and during these periods the status display is not up-dated. The validity of the busy control characters are tested and the interactive message is displayed on the lower half of the viewdata receiver. Receipt of a valid character causes a reply message to be sent to all active outputs. A typical busy reply frame is shown in Figure 4. Such frames are transmitted when the related busy choice number is received. The reply overwrites the busy choice display leaving the status display intact for operator convenience. Following a valid busy choice, a three-digit character string is received fron the active input and formed into a port number or code number. This number is checked for validity in relation to the chosen busy command, and an error-message sent if the number is incorrect. If the busy choice requires a second number, for the operation chosen, the above operation is repeated. In addition, the two numbers are checked tonsure that the second entry is equal or greater than the first before proceeding. After all required input has been received the busying operation is carried out and the normal display of status resumed. The apparatus also has an error checking facility which can detect the following error states: 1) A modem on line but no carrier signal detected within 20 seconds of modem on line detection. 2) A carrier signal detected but no transmission data detected within 2 seconds of the first detection of the carrier signal. Errors are detected by checking the contents of the memory 31 for each port and when an error state is detected the busy control output for that port is set on. An error report message is transmitted to all the outputs of the circuit 37 together with printer control characters to enable a printed record to be made at appropriate control centres which are equipped with printers. When an error is detected the lower half of the display is over-written by the error message leaving the status display intact for the period of the error display. The error message is maintained for 1 minute before normal operation of the apparatus 20 is restored. A flowchart illustrating one example of the way in which the microprocessor can be programmed is given in Figures 5a to 5c, 6a to 6c and 7a to 7c.

Claims: CLAIMS 1. Apparatus for monitoring the access ports of an information store of a data transmission system characterised in that it comprises means (30) for sequentially scanning the ports, means (31) linked to said scanning means for storing information indicative of the condition of each port, and means (37) responsive to data received from said storing means to generate a data signal or signals indicative of the condition of a port for transmission to a monitoring location. 2. Apparatus as claimed in claim 1 and comprising a microprocessor (30) which is arranged to scan a plurality of latches (35) each of which is associated with one of said ports. 3. Apparatus as claimed in claim 2 wherein the microprocessor (30) has an associated random access memory (35) which stores data indicative of the condition of said ports and which is updated cyclically as the latches (35) are scanned. 4. Apparatus as claimed in any preceding claim wherein the data transmission system is a viewdata system and the monitoring location includes a conventional viewdata terminal which is linked to said generating means (35) and is arranged to display information relating to the condition of each port. 5. Apparatus as claimed in claim 4 wherein the condition of each port is represented by a geometric shape (50) on a visual display unit, the colour of geometric shape being indicative of the condition of the associated port. 6. Apparatus as claimed in claim 5 wherein said shapes (50) are displayed as a matrix of m by n characters.

Inventors: CANTWELL, BRIAN DAVID
Applicants: THE POST OFFICE
Application year: 1981
Main classification: H04L11
IPC codes: H04M11, G06F13, H04N17, H04L29, H04L12