Conversational Video System

The present invention relates to two-way video communication systems and particularly to such systems capable of providing subscriber to subscriber video data communication in a conversational mode.

Communications systems for transmitting data point to point are well known, such as conventional telex systems and data base access systems. In addition, of course, telephone systems are well known two-way conversational communication media with the disadvantage being that a telephone system does not provide any hard copy nor does it allow you to, on the same device, obtain supplementary data while carrying on the conversation. Such supplementary data may be particularly important if the purpose of the conversation is commodity dealing such as in the money market. With respect to the telex communication, apart from its associated rate of speed, it does not enable you to readily carry on two different two-way telex communications alternatively so that you can carry on "telex conversations" with two different subscribers at substantially the same time. Moreover, neither the telex communication systems nor telephone communication systems provide a listing of incoming callers prior to acceptance of the message by the recipient. With respect to two-way data-base access systems, such prior art systems do not in reality provide a real-time conversational communication in that they merely provide for remote storage of information which may subsequently be retrieved upon request by subscriber or, in certain instances can be provided to the subscriber if he is accessing the particular storage location to which the data is being provided. However, this is still not a real-time conversational type of video communication system in which a pair of subscribers or users can interact in real time in a conversational mode. With respect to prior art telephone and data-base access systems, a prior art system merging these two technologies is known as the Delphi system which is a telephone message management system in which speech messages may be pre-recorded and stored in a data base for subsequent automatic transmission to incoming callers and in which incoming messages may be stored for subsequent later transmission to proscribed recipients. However, this system is not a true conversational video communication system or does it enable a particular user to carry on multiple conversations substantially simultaneously. Thus, there are no satisfactory prior art systems known to applicants which are capable of providing interactive conversational type of video data communications between pairs of users or subscribers nor such systems which enable multiple conversations to be carried out by a given user or subscriber in real-time and in association with data-base retrieval of supplementary data. These disadvantages of the prior art are overcome by the present invention.

A video conversational data communication network in which subscribers may conduct conversational video textual data communications with one or more keystations the network. Each keystation is associated with a keystation terminal controller interface which is in turn connected to a message switching node for routing calls throughout the network. The keystation controller interface locally stores video conversational textual data for its associated keystations and enables two different designated keystations to conduct two different video conversations with a common keystation in a split screen display. The split screen display may also be used to display retrievable data from a data base for simultaneous display along with a video conversation. The video conversational textual data is transmitted between connected keystation controller interfaces in packets which contain less than the total displayable data content of the conversational video textual data message input via the keyboard. The keystation controller interface also enables preparation of responses prior to transmission to the other party and while receiving a transmission from that party. Prior to completion of a call, the keystation controller interface provides an incoming calls queue video display at the connected keystations. This video display may contain a unique identifier for each keystation initiating a call as well as an interest message. The receiving keystation may then randomly select any of the displayed incoming calls irrespective of position in the queue and the video conversation may then take place using the associated keyboards and video displays. A hard copy print out of the video conversation may then be obtained on a printer.

FIG. 1 is an overall system functional block diagram of a conversational video system in accordance with the present invention;

FIG. 2 is a functional block diagram of a typical central system network portion of the conversational video system of FIG. 1;

FIG. 3 is a block diagram of a typical host computer portion of the central system network of FIG. 2;

FIG. 4 is a block diagram of a typical computer node portion of the packet switching network of FIG. 2;

FIG. 5 is a block diagram of a typical concentrator computer portion of the central system network of FIG. 2;

FIG. 6 is a functional block diagram of a typical terminal controller for use in the conversational video system of FIG. 1;

FIG. 7 is a functional block diagram of a typical display driver portion of the terminal controller of FIG. 6;

FIG. 8 is a more detailed functional block diagram of the VK8-A display driver of FIG. 7;

FIG. 9 is a diagrammatic illustration of a typical keyboard layout for the keyboard portion of a typical keystation for use in the system of FIG. 1;

FIGS. 10A-10F are diagrammatic illustrations of typical sample conversational video displays which may appear on the display portion of a typical keystation used in the system of FIG. 1;

FIG. 11 is a diagrammatic illustration of a typical display area layout for the display portion of a typical keystation used in the system of FIG. 1;

FIG. 12 is a diagrammatic illustration of the splitting of an input message to the concentrator computer into multiple packets; and

FIGS. 13A-13P are diagrammatic illustrations of a typical conversational signal path in the system of the present invention, with FIGS. 13A-13F relating to setting up a call, FIGS. 13G-13I relating to ending a call, and with FIGS. 13J-13P relating to leaving a call.

Referring now to the drawings in detail and initially to FIGS. 1 and 2 thereof, an overall system functional block diagram of a conversational video system, generally referred to by the reference numeral 30, in accordance with the present invention is shown. As shown and preferred in FIG. 1, the conversational video system 30 of the present invention preferably includes a central system network 32, to be described in greater detail with reference to FIG. 2, and a plurality of subscriber locations with two such subscriber locations 34 and 36 being shown by way of example in FIG. 1 although, of course, any plurality of subscriber stations can be utilized in the conversational video system 30 of the present invention. As illustrated in FIG. 1, the central system network 32 preferably includes a host computer 38 which, as will be described in greater detail hereinafter, serves as the traffic control manager for the central system network 32 and is preferably a conventional computer such as a Digital Equipment Corporation PDP11/70. The host computer 38 is preferably connected to a packet switching network 40, which, as illustrated in FIG. 2, preferably comprises a plurality of computer nodes with two such nodes 42 and 44 being shown by way of example in FIG. 2. The packet switching network is preferably connected to concentrator computers located at the various geographic locations close to the various subscribers with two such concentrator computers 46 and 48 being illustrated in FIG. 1 as being associated with subscribers 34 and 36, respectively. As will be described with respect to FIG. 2, these concentrator computers 46, 48, if located at the same site as the associated computer node may be directly connected thereto; however, if located at a remote site from the computer node, then they will be connected to the particular computer nodes in the packet switching network 40 via conventional modems. The concentrator computers 46 and 48 also preferably receive retrievable data from a retrievable data-base such as data-bases 50 and 52, respectively, which provide supplementary data for retrieval and display at the various subscriber locations 34, 36 by way of example. The associated concentrator computers are preferably connected to the various subscriber stations, such as 34, 36 via conventional modems, such as modems 58 and 60 for concentrator computer 46 and modem 62 for concentrator computer 48, to the subscriber locations 34, 36, respectively, with modem 58 being connected via telephone land line 64 to another conventional modem 66 and therefrom to a terminal controller 68, to be described in greater detail hereinafter with reference to FIGS. 6 and 7. The terminal controller 68 is in turn connected to a plurality of subscriber keystations with each terminal controller preferably being capable of servicing, by way of example, up to 6 such subscriber keystations. Each keystation, such as keystation 70 illustrated in FIG. 1, preferably includes a keyboard 72, associated keyboard logic 74 and a cathode ray tube display screen 76 for display of supplementary data and conversational data. As will be described in greater detail hereinafter, the keyboard 72, together with the keyboard logic 74 provides the conversational data to the terminal controller 68 which acts as the interface between the keystation and the central system network 32 to enable conversational video messages to be transmitted and received in a real-time interactive environment. As further shown and preferred in FIG. 1, each terminal controller, such as terminal controller 68 also includes an associated printer 78 for providing a hard copy of the video conversation which has been displayed at the particular keystation through which the conversation has been conducted, such as keystation 70 by way of example. By way of example, subscriber station 34 is shown as having two terminal controllers, terminal controller 68 and terminal controller 80, each of which preferably has 6 associated keystations, with only 3 such keystations being illustrated in FIG. 1 for terminal controller 68, namely keystations 70, 82 and 84 and with only 2 such keystations 86 and 88 being illustrated for terminal controller 80 which is also associated with a separate printer 90. Terminal controller 80, like terminal controller 68 is preferably connected to concentrator computer 46 via a conventional modem 92 and a telephone land line 94. Similarly, at subscriber station 36, at least one other separate terminal controller 96 is provided for controlling up to 6 keystations with, again, for purposes of illustration, only 2 such keystations 98 and 100 being shown in FIG. 1. In addition, a separate printer 102 is also associated with terminal controller 96 which is, in turn, connected to concentrator computer 48 via another conventional modem 104 and a telephone land line 106. As will be described in greater detail hereinafter, the concentrator computers 46, 48 for example, are preferably conventional computers such as Digital Equipment Corporation PDP11/34 and the respective terminal controllers, such as 68, 80 and 96 are preferably special purpose computers such as Digital Equipment Corporation PDP8/420A which preferably contain a special purpose conversational video control program to be described in greater detail hereinafter.

Referring now to FIG. 2, a more detailed block diagram of the central system network 32 of FIG. 1 is shown. It should be noted that the central system network 32 illustrated in FIG. 2 is merely exemplary of one possible network configuration although many other possible network configurations for providing conversational video may be accomplished without departing from the spirit and scope of the present invention. Thus, as shown by way of example in FIG. 2, the packet switching network 40, as previously mentioned, preferably contains two computer nodes 42 and 44, such as conventional Digital Equipment Corporation PDP11/34 computers which are illustrated as being geographically situated at the same location although, of course, these nodes could be at different geographic locations and, moreover, any desired plurality of nodes at different locations could be provided in accordance with the conversational video system of the present invention. However, for the purposes of explanation, it shall be assumed that the central system network 32 has the configuration illustrated in FIG. 2. Moreover, it shall be assumed, for purposes of explanation, that the conversational video system 30 of the present invention is capable of providing world-wide conversational video to subscribers located at five different geographical country sites, such as London, New York, Paris, Zurich and Frankfurt, by way of example. In this regard, it shall be further assumed that the computer nodes 42 and 44 are located at one of these geographical country sites, such as London, as illustrated in FIG. 2. Each of these geographical sites preferably has its own associated concentrator computer and it shall be assumed that concentrator computer 46 is located at Frankfurt in the example of FIG. 2, concentrator computer 48 is located at Zurich in the example of FIG. 2 and that additional concentrator computers 110, 112 and 114 are located, respectively, at London, Paris, and New York in the example of FIG. 2. In addition, preferably each concentrator computer 46, 48, 110, 112 and 114 has its own associated data-base for providing retrievable supplementary data for display at the keystations associated with that particular concentrator computer. Thus, the London data-base is designated by reference numeral 120 and the New York data-base is designated by reference numeral 122. It should be noted that as illustrated in FIG. 2, the retrievable data-base may also be remotely located or shared such as in the instance where the Zurich data-base 52 is also accessed by the Paris concentrator computer 112 via conventional modems 124 and 126. The concentrator computers 46, 48, 112 and 114 are shown as being remotely located from the computer nodes 42 and 44 and thus, are preferably connected thereto via conventional modems and telephone land lines, with concentrator computer 114 being connected to computer node 42 via modems 130 and 132 and telephone land line 134, with concentrator computer 112 being connected to computer node 42 via conventional modems 136 and 138 and telephone land line 140, with concentrator computer 48 being connected to computer node 44 via conventional modems 142 and 144 and telephone land line 146, and with concentrator computer 46 being connected to computer node 44 via conventional modems 148 and 150 and telephone land line 152. With respect to concentrator computer 110, assuming it is located at the same physical location as the computer node 44, then it may be connected thereto by direct connection. However, if the concentrator computer 110 is remotely located from computer node 44, then it would preferably be connected thereto via another pair of conventional modems 154 and 156, shown in dotted form, and a telephone land line 158 which, of course, would be replaced by a conventional wire connection in the instance where the concentrator computer 110 is located at the same physical location as the computer node 44. The various modems associated with the connection of the respective concentrator computers 110, 46, 48, 112 and 114 are illustrated in FIG. 2 in one block corresponding to a plurality of such modems with these blocks being labelled, respectively, with reference numerals 170, 172, 174, 176 and 178. Modems 58, 60 and 62 in FIG. 1 are just an example of such modems and it should be noted that preferably one modem is provided for each telephone line connection such as preferably one per terminal controller, not taking into account a stand-by or back-up situation in which an additional modem would be provided.

Referring now to FIG. 3, a typical hardware configuration for the host computer 38 is shown. Thus, as previously mentioned, the host computer may be a conventional PDP11/70 CPU having desired core, such as 256 K or 512 K words of core which, via a conventional Digital Equipment Corporation Unibus 200 is connected to associated direct access storage 202 and 204, such as an RX11 dual floppy disc and an RM03 disc via a conventional interface therefor, such as an RWM03 interface 206, for disc 204. In addition, a plurality of serial interfaces 208, 210, 212 and 214, such as a Digital Equipment Corporation DL11, are provided for interfacing the CPU 38 with various associated control consoles, such as interface 208 being utilized with the control console associated with start-up of the system, interface 210 being associated with the control console for the conversational video communication of the system, interface 212 being associated with the control of the packet switching network 40 and with interface 214 being associated with the control which enables identification of new subscribers to be put into the system so that they may be incorporated into the conversational video system 30. In addition, a conventional asynchronous serial line interface 216, such as a conventional Digital Equipment Corporation DMC11, is provided to connect the CPU38 to the packet switching network 40 for transferring data and control information between the host computer 38 and the packet switching network 40 at a rate of preferably 56 kilobits per second.

Referring now to FIG. 4, a typical hardware configuration for a typical computer node, such as node 42, for example, is shown. Thus, as previously mentioned, the CPU is preferably a conventional computer, such as a PDP11/34 having 124K words of store. The CPU 42 is preferably connected to associated storage and interface devices via a conventional bus 230, such as a Digital Equipment Corporation Unibus. As with the aforementioned host computer 38, the node computer 42 preferably includes additional storage 232 such as an RX11B dual floppy disc which is preferably used to boot the CPU42. In addition, a plurality of serial interfaces 234, 236 and 238, such as conventional Digital Equipment Corporation DL11 interfaces, are provided to interface with control peripherals such as the operators console to start up the system, the printer primarily used for failure monitoring, and the operating control for the system, respectively. In addition, a multiple serial interface 240, such as a conventional Digital Equipment Corporation DV11 is provided for interfacing with other node computers such as node computer 44. Interface 240 is capable of servicing up to 8 lines and may be connected to remotely located computer nodes via modems, 242 and 244 for example, and telephone land lines. The transmission rate is 9600 bits per second to the other nodes. In addition, in the example of FIGS. 2 and 4, computer node 42 includes 3 asynchronous serial line interfaces 246, 250 and 252, such as a conventional Digital Equipment Corporation DMC11, for interfacing the CPU42 with the host computer 38, and concentrators 112 and 114, respectively to enable communication between the CPU42 and the interconnected computers. With respect to concentrators 112 and 114, as was previously mentioned, they are interconnected to the computer node 42 via modems 138 and 132, respectively. With respect to computer node 44, since the concentrator computer 110 is, by way of example, located at the same site as computer node 44, no modem would be required between the corresponding asynchronous serial line interface and the concentrator computer 110. In addition, with respect to the interface 246, to the host computer 38, the data rate is preferably 56 kilobits per second. Lastly, the node configuration illustrated in FIG. 4 also preferably includes a cyclic redundancy check calculation unit 254, such as a conventional Digital Equipment Corporation KG11, connected to the computer bus 230 for conventionally checking the integrity of the transmitted packets. It should be noted that with respect to the interface to the concentrators at interfaces 250 and 252, this is preferably at a data rate of 9600 bits per second.

Referring now to FIG. 5, a typical hardware configuration for a typical concentrator computer, such as concentrator computer 46 is shown by way of example. Thus, as previously mentioned, the concentrator computer 46 CPU is preferably a conventional computer such as a Digital Equipment Corporation PDP11/34 having 124K words of store and which is preferably connected to various associated interfaces and storage via a conventional bus 270 such as a Digital Equipment Corporation Unibus as was previously discussed with reference to the configurations of FIGS. 3 and 4. Again, as was true with respect to the configuration of FIG. 4 for a typical node computer 42, 3 serial line interfaces, 272, 274 and 276, such as conventional Digital Equipment Corporation DL11 interfaces are provided for essentially the same purposes as interfaces 234, 236 and 238 previously described with reference to FIG. 4. Similarly, a cyclic redundancy check calculation unit 278 is also provided for essentially the same purpose as cyclic redundancy check calculation unit 254 in FIG. 4, such as a Digital Equipment Corporation KG11, and dual floppy disc storage 280, such as an RX11B, is provided for essentially the same purpose as the storage 232 in FIG. 4. An asynchronous serial line interface 282 is connected to the bus 270 for interfacing the concentrator computer 46 with its associated computer node 44 through modem 148 and telephone line 152 with the data being provided at a data rate of 9600 bits per second. In addition, the concentrator configuration also preferably includes a plurality of multiple asynchronous serial line interfaces 284, 286, 288, such as conventional Digital Equipment Corporation DH11 interfaces, each capable of supporting 16 lines which via conventional modems, such as the modem configurations represented by reference numerals 172, 290 and 292, connect the concentrator CPU46 to the various subscriber terminal controllers, such as terminal controllers 68 and 80 for example. It should be noted that preferably one modem is provided for each of the 16 telephone lines associated with the respective interface 284, 286 or 288 and, in the example of FIGS. 1 and 5, modem configuration 172 includes modems 58 and 60 illustrated in FIG. 1. The data rate on each of the lines connected to the subscriber terminal controllers, such as controllers 68 and 80, is preferably 1200 bits per second.

Referring now to FIG. 6, a functional block diagram of a typical preferred terminal controller configuration, such as terminal controller 68 which acts as the conversational video communications interface between its associated keystations 70, 82 and 84, by way of example, and the concentrator computer 46 which interfaces the terminal controller 68 with the balance of the conversational video communication system 30 is shown. As shown and preferred in FIG. 6, the terminal controller 68 preferably includes a central processing unit 300, such as a Digital Equipment Corporation KK8A CPU and associated memory 302, 304 and 306. Memory 304 and 306 are preferably core, each comprising 16K words, such as provided by a conventional Digital Equipment Corporation MM8AB Core. Memory 302 preferably includes memory extension logic, power fail logic, and ROM, with this logic circuitry being conventional such as a Digital Equipment Corporation KM8A. As will be described in greater detail hereinafter, the control program for the terminal controller 68 which controls the conversational video communication between the associated key stations 70, 82, 84 and keystations located throughout the conversational video communications network 30 is preferably downstream loaded into core storage 304, 306 of the concentrator computer 46, although, if desired, this control program could be permanently stored in ROM, assuming the ROM was of the appropriate capacity to store the control program. An example of a typical conversational video communications control program which is downstream loaded into core 304, 306 or which, as previously mentioned, could be permanently stored in appropriate ROM at the terminal controller 68 is provided below in Table A, written in PAL8 assembler language.

In the present example, where the above control program of Table A is downstream loaded from the concentrator computer 46, a terminal bootstrap program is stored in ROM 302. As was previously mentioned, this ROM 302 is contained in a conventional KM8A module. The bootstrap program is preferably responsible for loading the conversational control program of Table A into core 304, 306 as well as for loading other conventional executive programs into core 304, 306 which enable the proper operation of the CPU 300. An example of a typical preferred terminal controller bootstrap program stored in ROM 302 is provided below in Table B with this program also being written in PAL8 assembler language.

As further shown and preferred in FIG. 6, the terminal controller 68 also preferably includes conventional cyclic redundancy check logic 308, such as a Digital Equipment Corporation KG8 and a conventional multiple serial line interface 310, such as a Digital Equipment Corporation KL8A, for interfacing the terminal controller CPU 300 with the concentrator computer 46 via modem 66 at a rate of 1200 bits per second asynchronous, and for interfacing the terminal controller CPU 300 with the printer 78. In addition, the terminal controller 68 also preferably includes a display driver for each of the keystations, such as keystations 70, 82 and 84, associated with the terminal controller. Thus, since as previously mentioned each terminal controller is preferably capable of servicing up to 6 keystations, 6 identical display drivers 312, 314, 316, 318, 320 and 322 are provided with, for example, display driver 312 being connected to keystation 70, display driver 314 being connected to keystation 82 and display driver 322 being connected to keystation 84. Each of these display drivers 312 through 322 may preferably be of the type commercially available from Digital Equipment Corporation under the designation VK8A. Each display driver preferably provides video signals to the CRT associated with the keystation, such as CRT 76 for keystation 70, and receives input signals from the keyboard logic associated with the keystation, such as keyboard logic 74 for keystation 70, with the display driver 312 through 322, inclusive, being the interface between the CPU 300 and the individual keystations.

Referring now to FIG. 7, a typical video display driver 312 is illustrated in block form. Thus, the display driver 312 preferably includes a plurality of input gates 350 for receiving the eight data lines from the keyboard encoding logic 74, as well as for receiving a KEYBOARD PRESENT signal line also provided from the keyboard logic 74 to indicate to the terminal controller 68 that the keyboard has been switched on. In addition, the display driver 312 also includes conventional strobe logic 352, which receives a keyboard strobe signal from the keyboard logic 74, and control, address, and data registers 354, 356 and 358, respectively. Control register 354 preferably provides an alarm control signal to the keyboard for providing an alarm indication to the user. The address register 356 and the data register 358 are preferably associated with a display memory 360, such as a display RAM having 2048 bytes of memory. In reality, the display screen is preferably 80 to 24 and, accordingly, only the first 1920 bytes of the display RAM 360 are utilized to map 1-to-1 on to the display screen. The output of the display RAM 360 is provided to a conventional video signal generator circuit 362 which includes a character generator for providing a video display signal to the CRT 76 from the contents of the display RAM 360. As shown and preferred in FIG. 7, the input gates 350, strobe logic 352, control register 354 and address and data registers 356 and 358, respectively, are all connected to the CPU bus 370, such as a conventional PDP8 Omnibus. As was previously mentioned, the display driver 312 is preferably a conventional display driver such as a VK8A commercially available from Digital Equipment Corporation and a more detailed block diagram of such a VK8A display driver is illustrated in FIG. 8 and corresponds to FIG. 3-1 in the VK8A Maintenance Manual of January 1977 which may be referred to for further details on the operation of the VK8A display driver.

Referring now to FIG. 9, a diagramatic illustration of a typical keyboard layout for the keyboard portion 72 of a typical keystation 70 for use in the conversational video system 30 of the present invention is shown. Thus, as shown by way of example in FIG. 9, the various keys of keyboard 72 bear legends associated with the function or type of message which the user or keystation 70 wishes to transmit through the keyboard logic 74 to the terminal controller 68, for example, for appropriate processing. As further shown and preferred in FIG. 9 the keyboard function keys are preferably divided into several functional types; namely mode keys 700 which select between a data base display mode, such as for displaying conventional data of the type commercially available from Reuters under the service designated as Reuter Monitor, and the conventional video communication mode which enables a user to carry on a two-way conversation with other users in the system 30; function and control keys 702 which are responsible for certain functional control commands; display and cursor control keys 704 which are responsible for controlling the display 76; and character control keys 706 which include certain character control functions including insertion of character data. The depression of a mode key 700 preferably causes subsequent input to be interpreted by the terminal controller 68 as being associated with that selected mode. With respect to the function and control keys 702, the effect of each function key is to some extent preferably dependent upon the mode which has been selected. Thus, the key labelled VIEW indicates to the terminal controller 68 that the characters which are subsequently being input via the character control keys 706 are to be interpreted as a request for a display. The key labelled CONTACT indicates to the terminal controller 68 that the characters which are subsequently input via the character control key 706 specify the party or subscriber with whom a conversation or other contact is desired. The key labelled ACCEPT indicates to the terminal controller 68 that the character which is subsequently input via the character keys 706 specifies the call that the user wishes to accept from the incoming call list. The key labelled INSERT indicates to the terminal controller 68 that the characters which are subsequently input via character keys 706 are to be interpreted as an insert whose function depends on the mode selected; for example, in the data or Monitor mode the characters would be interpreted as an insert to the data base 50 whereas in the conversational mode the characters which were input would be interpreted as an insert to the user line of the display 76 allowing prepreparation of conversational text without transmission at the time of preperation of these characters to the other party to the communication. This key may also be used to prepare messages to be left as will be described hereinafter. The key labelled CANCEL indicates to the terminal controller 68 that the characters which are subsequently input by character key 706 are describing an entity to be cancelled. The key labelled RESET resets a keystation within the current selected mode such as clearing the input characters displayed on the insert line and the associated measage line. In addition, as is readily available from the Reuter Monitor system, news alerts can be provided, and, if such a data base is used to provide data to the system 30 of the present invention, then the RESET key, if qualified by an earlier ALRTS key from key group 704, may be used to clear a news headline, with the display 76 reverting to the mode before the ALRTS key was depressed. The key labelled RECLL provides a control signal to the terminal controller 68 requesting the recall of the previous display. The key labelled INTPT initiates a control signal to the terminal controller 68 which, in the conversational mode, initiates an interrupt message given control of the conversation over to the party which initiated the interrupt message. This function is to be described in greater detail hereinafter. The key labelled END CONT initiates a control signal which results in the termination of a current conversation in the conversational mode. The key labelled CHGE CNV initiates a control signal which causes transfer, in the conversational mode, between conversations if two conversations are being carried on simultaneously by a single user 70 in which instance, as will be explained in greater detail hereinafter, the first conversation area 502 and the display area 504 are then utilised in the user display 76. The key labelled PRINT initiates a control signal to the terminal controller 68 which forces printing of the current display at printer 78.

With respect to the aforementioned key labelled ALRTS in key group 704, this key initiates a special sub-mode which allows control of the news headline area if present, the alerts area and the incoming calls area of the display 76. In this regard, when this key is initially depressed the alerts area is selected and control moved between the aforementioned three areas by pressing 1, 2 or 3 respectively. When the alerts or incoming calls area of the display 76 are selected the area may preferably be scrolled using the line and page control keys 704. With respect to these keys the LINE BACK and LINE FWD keys move the display up or down by one line and preferably affect only conversational dialogue displays, alerts and incoming calls, whereas the PAGE BACK and PAGE FWD affect the display of the next or previous page. With respect to the cursor control keys, these control the cursor, with the HOME key placing the cursor on the first position of the insert line and with the TAB key placing the cursor just after the last character on the insert line, with these keys only affecting the cursor in the insert line. The key labelled TRANSMIT, in the conversational mode, transfers control of the conversation to the other party. This key is also used to indicate the completion of entry of text into the insert line. With respect to the key labelled ABBRV, this key relates to the insertion of text on the user line, and particularly to the insertion of such text containing abbreviations. When this key has been depressed, the terminal controller 68 will examine the inserted message after it has been completed to determine if any of the character strings correspond to abbreviations contained in the look up table of the terminal controller 68. If so, these character strings are expanded into their corresponding full text prior to transmission. With respect to the key labelled END LINE, this key initiates the starting of a new line of conversational video text without transferring control to the other party to the conversation. With respect to the key labelled HIGHLIGHT, in the conversational mode, depression of this key causes the previous line, or the current line if it has been started, to be highlighted by asterisks on the right of the text in the print out. Lastly, the pressing of any of the graphic keys results in the character being displayed in the position indicated by the cursor and the cursor moves on to the next position. It should be noted that the cursor normally remains in the insert line except during conversations when characters may be input directly into the display 76 for transmission to the other party.

Referring now to FIG. 11, a diagramatic illustration of a typical display area layout for the display portion 76 of a typical keystation 70 is shown. The display 76 preferably displays 24 lines each of 80 characters. Preferably the display 76 is divided into a plurality of pre-defined areas with certain of these areas clearly designated by providing lines 720, 722, 724 and 726. Thus, the screen or display 76 is preferably divided into a first conversation area 502 defined by lines 722, 720 and 726, with line 722 being at column 65, with line 720 being at column 14 and with line 726 being at column 22 to define a first conversation area of 8 by 64. In addition display 76 also includes a display area 504 defined by lines 722 and 720 which display area is preferably 13 by 64 and may display either the contents of a second conversation or retrieved data. Another area of the display is the incoming calls area 500 defined by lines 724, 722 and 726. The incoming calls area is preferably 11 by 15, with the last three lines of the incoming calls area 500 being special areas relating to a display of a message *MORE* if more calls cannot be shown, a display of the number of calls queued, a display of the number of left messages not cancelled, and a display of the last call received. The display 76 also includes an alerts message area 510 for display of alerts messages, with this area preferably being 6 by 15 and being defined by lines 722 and 724. Lastly, the bottom display area 506 of the display 76 includes a user insert line, a message area and a system status area with the bottom area 506 displaying the mode, the function, and the user insert line, which user insert line preferably comprises positions 11 to 80 of row 23, and with the mode of the system being displayed relating to the conversational mode including the CN1 or CN2 designation where CN1 is the conversation displayed in the first conversation area 502 and CN2 is the conversation displayed in the display or second conversation area 504. With respect to the message area, positions 1 to 48 of row 24 provides space for responses to inputs to the system from the keyboard 72 with this message area being cleared when text on the insert line is transmitted. Typical responses appearing on the message line are ACCEPTED and INVALID. Position 50 of row 24 preferably shows the transmission state of the last message in the current mode with W indicating waiting for transmission and T indicating waiting for a reply. This transmission state is preferably blank in the CN1 and CN2 modes, except when leaving a message. Positions 52 to 57 of row 24 preferably show the first 6 characters of the last page requested in the current mode, which page can be requested again by pressing the RECLL function key on the keyboard 72. Positions 59 to 60 of row 24 preferably show the status of the second conversation in the event this second conversation is not then currently being displayed in display area 504, with the first character being a single letter representation of the status, such as busy, queued, free, receive, send, transfer, ended or off system. With respect to the aforementioned alerts contained in area 510, preferably five alerts of up to 15 characters can be displayed in chronological order, with the most recent five received by the controller 68 preferably being displayed although the controller 68 is preferably capable of retaining an additional 12 alerts which may be scrolled into view by pressing the ALRTS key on the keyboard 72 and the LINE or PAGE keys. Preferably, as illustrated in FIG. 11, the most recent or last alert is not scrolled and always occupies the bottom line of area 510. With respect to the aforementioned incoming calls area 500, this area preferably contains brief details of the incoming calls and their interest messages, with the calls being shown in chronological order, with the oldest at the top of the area and with the latest call being displayed in lines 21 and 22. It should be noted, however, that the incoming calls do not have to be selected by the called party in the order in which they are displayed. Line 20 is preferably used to show the incoming call status. Preferably, if a news alert is received, it will be displayed in three lines below the display area 504, namely in rows 14 to 16 and positions 1 through 64. If a conversation is occupying this portion of area 502, then the heading of the conversation will be moved to row 17 to allow for display of the news alert. As was previously mentioned, this news alert may be reset.

Referring now to FIGS. 10A through 10F, these figures illustrate typical examples of conversational video displays which may appear on the display 76 of a typical keystation used in the conversational video system 30 of the present invention. As was previously mentioned, in order to conduct a conversational video communication, the keyboard 70 must be in the conversational mode. In this mode, each keystation is preferably capable of controlling two conversations simultaneously and, if the user decides to initiate such a second conversation, the details will be displayed on his display 76 in the display area 504 and will override and cancel any other display in this area 504. Displays, however, may be called up in any mode while a second conversation is in progress and will then temporarily suppress the display of the second conversation in area 504. These displays will themselves be overriden and cancelled when the second conversation is subseqently selected. The format of the display of the second conversation in area 504 is preferably identical to that of the first conversation and occupies lines 1 to 8 of the display area 504. If one conversation contact has been executed, a subsequent contact is assumed to be a request for a second conversation with control being passed back to the first conversation by depression of the key labelled CHGE CNV on the keyboard 72 which key may thereafter be used to transfer at any time between the two conversations. If the first conversation is completed while a second one is still in progress, the second conversation still remains in the display area 504. Typical call headings which would be displayed under various conditions are illustrated in FIG. 10A with each of these call headings being appropriately labelled. Each subscriber is preferably assigned a unique four character short name and the user wishing to contact another subscriber merely presses the CNTCT key on his keyboard 72, then the short name of the subscriber and the TRANSMIT key. In making this contact, the calling party may use an abbreviated form of address, may add a two character reference code to the called name, which code is intended to indicate which of the called subscribers keystations the caller wishes to contact, or he may add a 14 character interest message to his call to indicate the reason for his call. This interest message is displayed in his conversation display at his first message in the conversation and is shown in the incoming calls area 500 of the display 76 of the party being called and then in his conversation display once the incoming call is accepted. Calls which are received by a subscriber are preferably assigned a letter on receipt and are displayed in the incoming calls area 500 of all keystation screens associated with that subscriber. Calls normally occupy one line of the incoming calls area 500 and are preferably displayed, as previously mentioned, in time order with the letter assigned to the call, the four character short name of the calling subscriber and, if present, the two character reference code indicating the particular keystation that the caller wishes to contact. If an interest message is sent with the call, it preferably appears on the next line of the incoming calls area 500 indented one space. When the user accepts a call by pressing the ACCEPT function key on his keyboard 72 followed by the letter identifying the call which he wishes to accept and the key labelled TRANSMIT. The system displays, on his insert line, the message CNV ACCEPT A assuming that call A is accepted, and in the conversation area 502 for the first conversation or the display area 504 for a second conversation, the conversation heading in exactly the same format as for the contacting subscriber except for the substitution of the word "FROM" for the word "TO" to indicate that the calling party originated the call. If an interest message was included with the contact, this is preferably displayed as the first message of the conversation and the contacted party is then expected to reply with a second message. The status of the call will reflect this. The acceptance of the call is also signalled to the terminal controller of the calling party and the status of the called party's display is updated to indicate either that he should await a message, such as if he sent an interest message, or that he should start the dialogue or conversation. In addition, the accepted call is cleared from the incoming calls area 500 of all keystations associated with that subscriber. With respect to conversations dialogue, input messages are preferably displayed in the conversation area 502 for the first conversation, starting at position 4, with the user keying in the information at his own rate. The message is then transmitted in packets as it is being typed in, with the packets of the message preferably being transmitted if a space character is encountered after the input of the tenth character from the start of the line or end of the previous packet, if no space is encountered after the tenth character but the 15th character has been input, if the END LINE key has been depressed either in conversation text or to release prepared text in the insert line, if the 61st character of a line is typed, this character overflowing to the next line and automatically forcing an end of line condition, if the control is moved to the insert line by pressing the INSERT key or the ABBRV key, if the TRANSMT key is pressed to indicate the end of the sender's message, if an interval of a pre-determined period, such as 20 seconds, elapses since the last text transmission, or if the END CONT key is pressed. The completion of a message is preferably signalled by a change of status in the conversation header line of the sender's conversation from send to receive and vice versa for the recipient's conversation. While the user is awaiting receipt of a message he may prepare his next response on the insert line. He may also prepare a message for transmission when he is in control of the conversation. In either case, he enters the appropriate conversation mode CN1 or CN2 using the CNV mode and the CHGE CNV key if necessary and then presses INSERT. The system will then transmit any text up to this point and move the cursor to position 11 of the insert line. The user may then enter up to 70 characters in the insert line and edit them as required, with this text only being released if the user presses TRANSMIT, END LINE or END CONT while he has control of the conversation. The text when released in this manner is transferred to the conversation area 502 or 504 if it is a second conversation, and transmitted to the other party, with the insert line being cleared. If the TRANSMIT key has been pressed, the text is regarded as forming the complete message and the conversation status changes to receive. The use of the END LINE key indicates that the user's message is not complete. The cursor is moved into the dialogue text at an appropriate point for input to continue. Further text may be added in the conversation or in the insert area if the insert key is pressed again. A correspondent who was waiting for a response from the other party may preempt control by pressing the INTERRUPT key, as previously mentioned, and any portion of text which has been received by the receiving party's terminal controller before the INTERRUPT key has been pressed is regarded as binding and is displayed on the recipient's display 76 as a received message. The pressing of the key changes the status of his conversation from received to send and results in an interrupt message indicating how many characters have been received by the interrupted party. Receipt of this message changes the status from send to receive, clears any text after the interrupt point, and displays the message *INTERRUPT* on the next line. The interrupter in then in control of the conversation and can commence the transmission of his message. He may in turn be interrupted. The display of a conversation holds a heading and up to 7 lines of conversation, each of up to 60 characters, by way of example. The first character of each line indicates whether the line was transmitted or received. The text of lines sent preferably start at position 4, lines received being indented to position 5. The most recent message is preferably at the bottom of the area and the oldest at the top. When the area is full, the uppermost lines are preferably moved off the screen leaving space for newer messages. Earlier parts of the conversations may be examined by using the LINE and PAGE function keys on the keyboard 72. It should be noted that when a conversation is scrolled so that the current line is not on display, this is indicated on the display by display of the word SCROLL on the heading line. A user may print a current conversation using the PRINT function key on the keyboard 72 at any time. If he does so, the conversation up to that point is released for printing on the printer associated with the terminal controller and, effectively, a new conversation is started within the same call and with the same party, the user's screen is cleared, and portions of the conversation which took place before pressing the PRINT key cannot be recalled by use of the LINE and PAGE keys. It should be noted that preferably conversations of a normal length of 300 to 500 characters may be completed without the necessity of printing the conversation before it is completed.

By way of example, with respect to the aforementioned abbreviations function, standard abbreviations may be employed such by using the symbol A for the word "AT" by using the symbol B for "I BUY", by using the symbol FF for "FRENCH FRANCS", and by using the symbol * for "MILLION", then the expression "AT 79 I BUY 10 MILLION FRENCH FRANCS" may be provided in the following abbreviation: "nA79B10*F". Simple conversational messages in accordance with the above principles are illustrated in FIGS. 10A through 10F and are essentially self-explanatory with the legends provided underneath. It should be noted that the above exemplary displays are assuming that the conversational video system 30 is being used in the money dealing market in which money dealing rates are proposed and accepted by the subscribers to complete transactions. Of course, the conversational video system 30 of the present invention may be employed in any type of rapid video communication between subscribers and particularly where more than one conversation is desired to be carried on at a given time or where it is desired to provide supplementary data which may be retrieved along with the conversational text, particularly where the data could be useful in connection with the transaction being carried out through the video conversation function of the system 30. As was previously mentioned, the display of retrievable data may preferably be conventionally accomplished by a conventional data retrieval system, such as the Reuter Monitor and need not be explained in any further detail. The operation of the system 30 of the present invention shall now be described in greater detail below. It shall be assumed for purposes of explanation that the conversational video system 30 of the present invention is being used in a money market dealing environment.

As was previously described, the terminal controller, such as terminal controller 68, provides the interface between the users or subscribers and the central system network 32. Preferably, the terminal controller 68 interface to the network is based on a port table in the controller 68 control program enumerated above in table A. The various ports relate to communication with the associated concentrator 46, separate ports corresponding to communication with the data base 50, other ports relating to communication with the host computer 38 through the packet switching network 40, and with 12 ports being reserved for the 12 possible video conversations that can be held on the 6 keystations supported by the terminal controller 68, such as keystations 70, 82 and 84, by way of example. As was previously mentioned, the packet switching network 40 is preferably a conventional type of packet switching network such as one conforming to the standardised X25 packet switching protocol, and is preferably used to provide logical connections between the various concentrator computers, such as 46 and 48, and between the concentrator computers 46, 48 and the host computer 38. The system is designed so that preferably one of the logical connections between the concentrator computer 46 and the host computer 38 through the packet switching network 40 also carries all of the communication information between the terminal controller 68 and the host computer 38 as well as, in the example of FIG. 1 all of the communication information between the terminal controller 80 and the host computer 38 and any other terminal controllers which are associated with that particular concentrator computer 46. Thus, all of the common ports of the terminal controllers which are connected to a given concentrator computer 46 and which are associated with the host computer 38 use the same channel across the packet switching network 40. Similarly, all of the video conversations that are directed from one concentrator, such as concentrator 46, to another concentrator, such as concentrator 48, are multiplexed across a common logical connection between the concentrators 46 and 48. The terminal controller, such as terminal controller 68, preferably contains answerback codes and user abbreviations which are employed in the conversational video system 30 of the present invention. Thus, an answerback code would preferably be a 20 character text string identifying a particular subscriber, such as subscriber 34, and the user abbreviations are for abbreviated transmissions of various data so as to expedite the video communication, with a given terminal controller preferably containing up to a thousand characters relating user abbreviations to their corresponding full text expansion. The terminal controller 68 is preferably identified to the concentrator computer by a subscriber identifier and a unique controller number. During system 30 operation, the various multiple serial interfaces 284, 286 and 288, by way of example, associated with the concentrator computer 46 check a line whenever no traffic has been acknowledged for a pre-determined period, such as 5 seconds. Each terminal controller acknowledgement confirms the identity of the line by preferably including a check byte in addition to the packet sequence number. If the checks fail, the connection is broken and an error condition is reported. The packets on the line to the terminal controller, such as terminal controller 68, may be at normal or high priority, to be described in greater detail hereinafter. Once a packet is being transmitted, it is preferably delivered before another is transmitted; however, the interface 284, 286 or 288 will preferably select high priority packets in preference to normal priority packets. The messages received by the concentrator computer 46 from the system 30 are preferably divided into 64 data byte packets for transmission to the terminal controllers, such as terminal controller 68, so that high priority packets can obtain access to the line in a reasonable time. The first byte of each packet to the terminal controller 68 preferably contains the port number of the connection and a bit indicating if this is the first packet of a message. In terms of the aforementioned priority, a video conversational message is preferably given a high priority in the system whereas data from the data base 50 is given a normal priority. Thus, an input message is normally divided into packets so as to enable a high priority packet to be inserted where necessary between normal priority packets so that the conversational video data may always take precedence over normal data transmission in the system 30. As shown in FIG. 12 which is a diagramatic illustration of the splitting of data messages into several packets, when an input message is split, the first 64 bytes, by way of example, can be transferred in the buffer they arrived in and the port number can replace the data length byte. The rest of that buffer is preferably copied into a second buffer which is chained to the first buffer. This preferably contains 1 byte for the port, 63 bytes for the remaining data in the original buffer and 1 byte to copy from the first byte of the second buffer. If a second buffer exists, this is split into two buffers in a similar way. High priority messages are preferably handled in the same way although they are preferably restricted to messages of less than 64 bytes.

When a keystation, such as keystation 70, wants to initiate a call or video communication the user depresses the CNTCT key on the keyboard 72, which, through the keyboard logic 74, provides a contact signal to the terminal controller 68. On detecting this contact signal, the terminal controller 68 preferably sends the contents of the user insert line for user 70 to the host computer 48 for analysis. As was previously mentioned, the message preferably includes a port number allocated for the conversation and a conversation reference byte. The user's keyboard 72 is preferably locked until the initial reply is received. The host computer 38 then sends the contact request as an incoming call to the respective terminal controller with which the message is associated, such as controller 96 along with the text for display and additional data to enable the call to be established when it is accepted by the controller 96 or by one of the users 98, 100 associated with terminal controller 96. Prior to acceptance of the incoming call by one of the keystations 98, 100, the call is placed in one of, by way of example, 16 positions in a dedicated buffer area in the terminal controller 96, with a separate list specifying the order of arrival of incoming calls which controls the display of the incoming calls on the CRT display 96 such as displayed in the incoming calls portion 500 of the display illustrated in FIG. 11. The display preferably shows the calls in order of arrival normally starting with the earliest received incoming call; however, preferably the latest call is always shown at the bottom of the incoming calls area 500 on the display. If the capacity of the incoming calls area 500 is exceeded so that not all incoming calls can be shown in the incoming calls area 500, then the incoming calls can be scrolled in this area; however, the latest call is always preferably left on display at the bottom of the incoming calls area 500. Any of the associated keystations 98, 100 and preferably accept any of the incoming calls displayed in the incoming calls area 500 and does not have to select the calls in the order of receipt. As was previously mentioned, the incoming calls may be displayed with an adjacent interest message which can be utilized by the users at the keystations 98, 100 to determine which call to accept first. When a user 98,100 desires to accept one of the displayed incoming calls, the user depresses the ACCEPT key on his keyboard 72, which, through the associated keyboard logic 74, transmits an accept signal to the terminal controller 96. The user, such as keystation 98, then indicates which of the displayed incoming calls he wishes to accept by inputting a single letter identifier displayed adjacent to the particular incoming call in the incoming calls area 500. The terminal controller 96 determines from this information which of the incoming calls have been accepted and uses the related data in the call buffer to set up a display heading for the incoming call, to report to the host computer 38, and to request a connection to the caller initiating the contact by sending a request on a dedicated port to the concentrator 48. This request preferably includes the subscriber 36 answerback code and the number of the keystation 98 accepting the call. This connection may, of course be successful or unsuccessful; however, if the connection is successful the relevant conversation area in the display such as the first conversation area 502 or the second conversation area 504 is initialised with a heading line. If, however, the connection is unsuccessful, a message is displayed in the message area 506. Assuming the connection is successful, the terminal controller 68 associated with the keystation initiating the contact will preferably reply with the subscriber 34 answerback code.

After the connection has been completed between the terminal controllers 68 and 96 and the associated calling and receiving keystations, such as keystations 70 and 98, respectively, the video communication conversation may then take place between these keystations 70 and 98. The conversation text is preferably held in 64 word buffers which are chained together in each of the respective controllers 68 and 96 with data for the printed heading preferably being held separately since it is placed in the text before printing of the displayed conversational video communication. The conversational control program provided by way of example in Table A, controls the text held in core 304, 306 and can provide scrolling of the display 76, regeneration of a conversation in the general display area 504 when required, and generation of displays in the conversation area 502 when this is affected by such things as alert messages such as corresponding to relevant supplementary data, such as important news stories which could affect the transaction being carried on between the callers 70 and 98. If the conversation is ended, or released for printing on printer 78 and 102, respectively, so as to provide a hard copy print-out of the communication between keystations 70 and 98, terminating information may be added before the text is queued to the printers 78, 102. In addition, as was previously mentioned in referring to the layout of keyboard 72, the keyboard 72 also preferably includes a HIGHLIGHT key for highlighting a particular line on the display, such as to indicate that a transaction has been completed if the video communication is used for such transactions as money market dealing, for example. The highlight control function preferably acts on the current or previous line and adds a row of asterisks to the conversation line. They are not displayed, as each line is limited to 64 characters, but rather appear in the hard copy print-out. The keyboard 72 interrupt key provides an interrupt control signal to the terminal controller 68 or 96, transferring control of the conversational dialogue from the party who is transmitting at that particular point in time to the party who is receiving, and causes the sending of a message to the then transmitting party to clear data from his screen which has not yet been transmitted to the receiving party. When the interrupt has taken place, the call buffers are modified appropriately and the conversation is again displayed with the deleted text removed from the display. In addition, a reply is sent acknowledging the interrupt so that an interrupt message appears on the screen or display of the party whose message has been interrupted.

Referring now to the user insert line which appears in display area 506 of the display 76, if either the insert key on the keyboard 72 or the abbreviation key on the keyboard 72 is depressed by the user during a conversation, this forces the cursor on the screen to move to the user insert line in display area 506 and provides a control signal through the terminal controller 68 or 96, depending who is initiating the insert function, to indicate that this function has been selected. Similarly, depression of the abbreviation key places the abbreviation character in the user insert line. The user then types in the desired insert message which is displayed on his user insert line. When the insert line is released by the user, such as by depression of transmit key, the end contact key or the end line key on the keyboard 72, it is treated by the respective controller 68 or 96 as a series of characters input from the keyboard 72. If the abbreviation character is found, then subsequent processing of the insert line by the terminal controller 68 or 96 is preferably in the abbreviation mode with each character string from the keyboard 72 preferably being tested by the controller to find if it corresponds to one of the abbreviations stored in the controller 68 or 96. Assuming it does correspond, then the abbreviation is replaced by its full text expansion and the expanded abbreviation is used as though the full text characters had been provided on the user insert line.

It should also be noted that preferably a message may be left by a caller when the conversation has not been accepted. This left message is preferably created on the user insert line and despatched by the sending terminal controller, such as controller 68 with an insert function, as a left message to the host computer 38 from which it is then sent in a message to the controller 96 of the party to which it is directed. This left message is then preferably printed on printer 102 and is preferably accompanied by the number of left messages which are being held in the host computer 38 for that subscriber 36. This number is preferably displayed in the incoming calls area 500 of the display 76 and is preferably flashed for a pre-determined period, such as 3 seconds, and is also maintained on a left message page of the subscriber 36 until it has been cleared or overwritten.

As was previously described, when a connection is made between the controllers 68 and 96, messages are sent over the line in packets which include cyclic redundancy checks and an acknowledgement protocol which gives a high probability of error free communication and ensures that packets are received in the order they were sent. Thus, packets which have been sent to the concentrator computer 46 or 48 preferably include a check byte specific to the controller 68 or 96, respectively, which enables any mis-connected line to be detected, with the check byte being loaded into the controller when the connection is established so that the concentrator computer may ensure that it is connected to the correct terminal controller. Preferably, the maximum packet size into the concentrator computer will hold 83 bytes of data with packets out to the terminal controller being preferably limited to 64 bytes of data. A message reaching the concentrator computer for the associated terminal controller may preferably contain up to 225 bytes with the messages thus being divided into up to four packets for transmission to the terminal controller. Preferably, the first packet in a message is marked to permit checks on message synchronisation. As was previously mentioned, there are preferably two priorities of message which may be received by the controller, namely high priority messages and normal priority messages, with one or more high priority messages being insertable between two packets of a normal priority message. The two priorities are therefore, preferably accepted by the controller as two independent packet streams.

Referring now to FIGS. 13A through 13P, a typical conversational signal path for conducting a conversational video communication in this system 30 of the present invention is shown. FIGS. 13A through 13F relate to the setting up of a call, FIGS. 13G through 13I relate to the ending of a call and FIGS. 13J through 13P relate to the leaving of a call, which is the aforementioned left message. For purposes of FIGS. 13A through 13P, it shall be assumed that the transaction relates to money market dealing and that the calling party is located in Zurich at keystation 98 and is known as the Zurich maker and the called party is located in London at keystation 602 and is known as the London taker. When user 98 enters a contact request, as was previously mentioned, the message with the current insert line is transmitted to his terminal controller 96, therefrom to the concentrator computer 48, and therefrom through the computer nodes 44 and 42 to the host computer 38. The insert line is then interpreted and if the address is a single character it is preferably expanded, as was previously mentioned, by accessing the address abbreviations from storage. If the address constitutes a list of subscribers, then this list is preferably held in core while the subscribers are contacted in turn. The host computer 38, which is also associated with the called party in the example of FIGS. 13A through 13P, checks to see if there is room in the called subscriber's queue and that the caller 98 is not inhibited. If the call can be queued, the terminal controller 96 is given an audit number for the call and the interest message which was input by the caller 98. When the terminal controller 96 receives this message it preferably clears the conversation area 502, assuming it is the first conversation, in the display 76 of the caller 98 to enable display of the conversational video communication and preferably places the heading on the first line and the interest message, if any, on the second line. If the call can be queued, then the host computer 38 sends details of the call to the connected terminal controller 600 for the called subscriber at which user 602 is located. This message preferably includes an audit number to reference the call and the time and date of the call. Upon receipt at terminal controller 600, the call is preferably given a reference letter and displayed in the incoming calls queue in incoming calls area 500 of the display 76 of user 602. If user 602 accepts the call, the call is removed from the calls queue on controller 600 and the controller 600 asks its concentrator computer 110 for a connection to terminal controller 96. Terminal controller 96 then validates the acceptance of the call and replies to terminal controller 600. If the call can be established, this reply preferably includes the associated identification of user 98. When the call has been established or rejected, controller 68 sends a message to host computer 38 stating the calls audit number, whether it has been established or rejected, and the current number of free keystations associated with terminal controller 600. In response, host computer 38 sends a message to delete this call with this audit number from all terminal controllers associated with the subscriber at which terminal controller 600 is located. With respect to the aforementioned incoming calls area 500, this is maintained by the terminal controller 600, for example, which performs a number of functions on it including display of the last call on the last two lines, display of the number of calls, display of a flashing asterick and sounding a buzzer to mark a new call, display of calls in order, removing accepted calls, display of a message indication such as *MORE* if not all calls can be displayed and the scrolling of the calls area, all of which are previously described.

Once the call has been established between the Zurich maker 98 and the London taker 602, conversational video text is sent in packets at prescribed intervals with each packet including a sequence number within the respective terminal controller 600 or 96 period of control. Packets are also preferably sent at intervals in each direction to confirm the link between users 98 and 602. If a text packet arrives out of sequence, the receiving controller 96 or 600 obtains control by preferably sending a communication failure message specifying the line and column of the last character correctly received with the conversation beyond this point being deleted and a suitable message being added, with the party whose controller 96 or 600 detected the error then being left in control to resume the conversation. If the communication is somehow broken, controller 96 or 600 treats this as an abnormal end of the conversation. When control is handed over at the end of a message, the packet includes the line number in the conversation to ensure that the line numbers are synchronized. The conversational video text is preferably held in data buffers in each controller 96 and 600 and is used to support the display 76 as well as being queued for printing on printers 102 and 604, respectively, at the end of the call. It should be noted that because the display is a 64 character display, text beyond column 64 would not be displayed, although it could be printed. As was previously mentioned, the party receiving a line of conversational video text may interrupt its receipt before this line has been completed by the originator. This interrupt function can preferably only be actioned from the keyboard 72 of the party receiving the line of text. As previously mentioned, the depression of the interrupt key on this keyboard sends an interrupt message to the party originating the line of text, specifying the line number in the call, and the last character in the line received. The user who has initiated this interrupt message then rejects any further input for the call and awaits a response to its request which response causes a message *INTERRUPT* to be displayed on the next line and gives the interrupting party control over the conversation. Assuming that user 602 has initiated an interrupt message, then controller 96 which receives this interrupt will remove any text in its conversation after the point specified, will add the aforementioned interrupt message indicator on a new line, and will reply to terminal controller 600 accepting the interrupt. Referring now to FIGS. 13G through 13I, the sequence of ending a call shall now be described. Assuming that user 98 now wishes to end the call, and is in control of the conversational video communication, the user 98 depresses the end contact key on his keyboard 72, thus sending an end contact message via terminal controller 96 to terminal controller 600. If , in the above example, user 602 has not just interrupted the conversation, then this end contact message is accepted, an indication message such as the word *END* is added to the display of user 602 in the conversation area being employed, 502 or 504, and a reply is sent via the concentrator computers 110 and 48, ending the logical link between users 98 and 602. If, however, the user 98 is not in control at the time he wishes to end the call, pressing the end contact key will cause an interrupt, followed in the same message by a request to end the call. When the end of call has been acknowledged, the controller associated with the party who has initiated the end of call message, reports to the host computer 38, giving direction as to the number of associated keystations now free and, if desired, additional call statistics. The other party to the conversation retains the call text on his display 76 until he also presses the end contact key, whereupon his associated terminal controller reports the same type of information to the host computer 38. It should be noted that preferably each controller, 96 and 600 preferably queues the text of the call for printing to printers 102 and 604, respectively, as soon as the end contact message has been actioned at that particular controller 96 or 600.

Referring now to FIGS. 13J through 13P, the sequence for leaving a message, if an attempt has been made to set up a call and the called party is busy or off the system, is illustrated. In addition, as previously mentioned, a message may also be left if a call has been queued and has not been accepted. When the message has been inserted on the user insert line of the calling party and the transmit key on his keyboard is depressed, a left message message could be sent to the host computer 38 and thereafter any acceptace of the call will be refused. Host computer 38 reads the left message data block for the subscriber and, if there are less than a pre-determined number of left messages held, such as 20, or if one of the previous left messages can be deleted, it places the new left message in storage 204. This left message is then sent to the appropriate terminal controller, such as terminal controller 600, for printing at printer 604 and will include the total number of left messages for the subscriber at which terminal controller 600 is located, with this number being flashed on all screens associated with that subscriber. A reply is then sent to the originating user 98 for display as well as being printed on printer 102 associated with terminal controller 96. The display area can then be cleared by pressing the end contact key which causes the printing of the message on printer 102 and the clearing of the display of user 98.

Summarising the conventional video system of the present invention, by the use of this system, it enables, through the use of a video display terminal, subscribers to contact any subscribers throughout a world-wide network, to conduct interactive conversations with these subscribers, to conduct two such conversations simultaneously with two different subscribers, to obtain supplementary retrievable data which can be displayed during the conducting of such a conversation and which may assist the caller in connection with the conversation, particularly if it is some type of dealing transaction in which such supplementary data may be helpful, it enables a called subscriber to receive a plurality of incoming calls and randomly select any one of these calls irrespective of time of receipt and dependent on certain parameters such as the identity of the caller and the interest message initiated by that caller, it enables hard copy print-out of the video communications, it enables pre-preparation of responses while an incoming message is being received, and it enables transmission of the video communication message in short segments facilitating rapid transmisssion and response without causing excessive load on the packet switching network. All of the above features help in providing an effective conversational video communications system of the type which will enable rapid subscriber to subscriber communication and completion of dealing transactions in such situations when the system is employed for that purpose.

It is to be understood that the above described embodiments of the invention are merely illustrative of the principles thereof and that various modifications may be carried out without departing from the spirit and scope of the present invention.