Title: Communications systems having a selective facsimile output

Description: This invention relates to switched communications systems including store and forward facilities for teleprinter apparatus and the like and more particularly to switched communications systems capable of selectively translating messages received from said teleprinter apparatus to stations employing facsimile equipment.

Communications systems which include store and forward facilities for teleprinter apparatus are conventionally employed to provide low cost, high speed information translation between remote locations where it is desired that the information translated be received in a hard copy format and telephony communication is not warranted, necessary or desirable due to such factors as time differences which may obtain between such remote locations, the nature of the information transmitted or the standard message volume involved. Where message volume does not justify substantial expenditures, access to such communications systems is available for intracompany communications through services provided for this purpose such as the Western Union Telex service. However, where message traffic is substantial, private communications systems employing leased lines for transmission are frequently developed.

Generally, switched communications systems including store and forward facilities for teleprinter apparatus and the like take either the form of a contention or polling arrangement wherein remotely located terminals, when given access to a line, transmit destination and message data to a central computer which functions to provide line access to each peripheral, receives and stores destination and message data therefrom and thereafter causes the transmission of such message data as has been received and stored to each destination peripheral defined by the destination data associated with a given message. In this manner, messages may not only be transmitted to a plurality of remotely located peripherals in a highly efficient manner, but in addition should certain specified destination peripherals be temporarily unavailable due to such factors as equipment or line malfunction, busy status conditions or inoperativeness due to the unavailability of equipment capable of operating in an unattended mode at locations not yet open to existing time differences or the like, the stored message may be subsequently forwarded when the defined destination peripheral subsequently becomes available through the establishment of an interrupt or other return condition at the central computer. In addition, should a later retransmission of a message be required by a specified destination peripheral, a previously stored message may be retransmitted from storage and such retransmission limited to previously defined destination peripherals through a scanning of the destination informtion stored with said message information. As will be appreciated by those of ordinary skill in the art, the message information transmitted to a central computer from a remote peripheral which includes teleprinter or teletypwriter apparatus will normally take the form of eight bit ASCII code groups representing the alphanumeric character information in the message to be conveyed.

In switched communications systems of the foregoing type which are organized according to a contention arrangement, each remotely located peripheral when requesting service may generate an interrupt at the central computer which is responded to in accordance with a fixed priority arrangement and the present availability of the central computer for the service requested. In a polling arrangement, the central computer periodically polls each peripheral on the line and any peripheral having a message to be transmitted when polled is given access to the line whereupon the message is transmitted to the central computer for storage and subsequent forwarding. Switched communications systems similar to those discussed above and suitable for adaptation in a private, intracompany or intra-agency dedicated system are disclosed in U.S. Pat. No. 3,403,383, which issued to H. G. KIENZLE, et al. on Sept. 24, 1968 and is assigned to Bell Telephone Laboratories, Inc.; in The Bell System Data Communications Technical Reference directed to the "85A1 Data Selective Calling System," dated April 1968 and published by the American Telephone and Telegraph Co.; and the articles devoted to the "Tele-Net" data communications network appearing in the May 26th, 1972 issue of The Digest as published by the Manufacturing Division Information Technology Group of Xerox Corporation and the Dec. 1970 issue of the D. P. Newsletter published by the Xerox Corporation.

Where dedicated or private switched communications systems including store and forward facilities have been established, messages which have been received at a designated destination peripheral, as printed by the teleprinter or teletypewriter apparatus in place thereat, are usually hand delivered to designated recipients without substantial delay. However, where the destination peripheral is at an extremely busy location, the destination peripheral is established at a highly populated location or the message is of extreme urgency, delivery time may become excessive and prompt telephone reporting may be insufficient due to the need for a hard copy. Furthermore, in dedicated systems such as those discussed above, the establishment of peripheral locations is dictated by traffic and usage considerations and hence locations which may be advantageously served by a peripheral device may not be deemed to warrant the same due to insufficient usage. This is particularly so in intra-agency or intracompany systems where a central location which may frequently house the central computer for the system is proximate to several outlying facilities which might otherwise have system peripherals located thereat but due to insufficient traffic patterns are required to rely upon a peripheral located at such central location whereby the intracompany or intra-agency telephone system is relied upon to provide initial advisory service that a message has been received at the central location with delivery of the hard copy of the message occurring subsequently through an intra location delivery service or the like. Furthermore, once dedicated or private switched communications systems including store and forward facilities have been established, the addition of peripheral stations to meet subsequently or temporary user requirements is often a costly and time consuming process and hence is generally avoided unless a well-defined and sustaining need is plainly demonstrated.

Those business or governmental users whose communication needs are such as to justify the establishment of a private or dedicated switched communications system which includes store and forward capabilities will invariably have an intracompany or agency telephone system in place at major sites and frequently such major sites will be linked by wats lines or the like to facilitate the substantial volume of telephone communication which must of necessity take place within the company or agency. In addition, the wide proliferation of portable facsimile equipment such as the Xerox 400 Telecopier series, provides another mode of information transmission which is readily available and produces a hard copy message format at relatively low equipment cost but at message cost levels which substantially exceed those associated with volume justified peripherals employing teleprinter or teletypewriter apparatus.

Facsimile apparatus such as relied upon in the Xerox 400 Telecopier series and the like basically transmit intelligence in the form of a modulated base band signal and to this extent facsimile information as transmitted is incompatible in format with that transmitted through a private or dedicated switched communication system relaying upon peripherals which include teleprinter or teletypewriter apparatus. In addition, facsimile equipment requires the completion of a plurality of handshaking functions between communicating transceivers prior to transmission to ensure that appropriate phasing and transmitter-receiver relationships are established and these handshaking functions too are basically inconsistent with the operation of a private or dedicated switched communication system including store and forward facilities and relying upon teleprinter or teletypewriter apparatus at the peripherals thereof. However, as facsimile apparatus such as represented by the Xerox 400 Telecopier series provides low apparatus cost, is easy to operate, exhibits low noise and may be placed in communication with a compatible transmitter through the telephone system in place by a mere dialing of the destination location and the subsequent placement of the telephone handset in the acoustic coupler thereof; it will be appreciated that if the same could be rendered compatible with information transmitted by a switched communications system employing teleprinter or teletypewriter apparatus it would represent an ideal, low cost, easy to operate peripheral for locations not warranting the installation of a peripheral employing teleprinter or teletypewriter apparatus. Furthermore, if only a receive mode peripheral is considered it will be appreciated that additional remote peripherals may be added to a dedicated or private system merely by adding appropriate telephone numbers to be dialed and where facsimile apparatus is normally maintained for other purposes, as is increasingly the case, the telephone numbers of each such location could be maintained in association with the dialing apparatus as a matter of course and employed, in conjunction with a company or public telephone system, for urgent messages even when a teleprinter or teletypewriter peripheral is available but not sufficiently close to the designated receiver to assure sufficiently rapid delivery. In addition, where the control computer and system dialing equipment is located at a central site surrounded by local peripheral plants or agencies, facsimile equipment in place at such peripheral plants or agencies could be relied upon, as a part of the switched communications system, to form a segment of the local distribution system in that messages received by teleprinter or teletypewriter apparatus at such central site could be reintroduced to said switched communication system and transmitted through the system and local telephone lines or telephone lines rented for a company or agency system directly to the desk of the designated addressee. Further, as such receive only peripherals when operating as a part of a switched communication system, would only be responsive to line information forwarded from teleprinter or teletypewriter peripherals through the store and forward facility, transmission time could be reduced as extensive information associated with document margins and the like is avoided while when not being employed in this manner as a receive mode peripheral, the overall utility of the facsimile apparatus acting in its own right would be retained. Thus, the ability to selectively incorporate facsimile stations into a switched communication system for teleprinter apparatus and the like would expand the flexibility of the resulting system to a wide degree while the expansion of the system to meet temporary or low level traffic requirements in a receive only mode could be achieved at relatively small additional expense.

Therefore, it is an object of the present invention to provide a switched communication system capable of accepting information in a digital format to be forwarded to a designated destination peripheral and forwarding such information in either a digital format or a facsimile format depending upon whether said designated destination peripheral is defined as a facsimile location or a digital location.

It is an additional object of the present invention to provide apparatus for receiving an input in the form of an ASCII code, for converting such ASCII code into an analog signal, for transforming said analog signal into a suitable facsimile format and for transmitting said transformed analog signal to a designated facsimile peripheral.

It is a further object of the present invention to provide controller apparatus for a switched communications system for enabling said switched communications system to transmit message information to facsimile equipment present at a designated peripheral.

It is another object of the present invention to provide controller apparatus for a switched communications system for accepting destination information and message information from a switching system and for responding to said destination information to establish a communications relationship with a designated facsimile peripheral and after said communications relationship has been established for converting said message information into a facsimile format, for transmitting said message information in facsimile format to said designated facsimile peripheral and for thereafter terminating said communications relationship.

It is an additional object of the present invention to provide a switched communications system having store and forward facilities for teleprinter apparatus and for facsimile apparatus acting in a receive-only mode.

It is a further object of the present invention to provide software controlled switching apparatus for a switched communications system wherein said software controlled switching apparatus is active to ascertain when a designated destination peripheral comprises facsimile apparatus and whenever such a designated destination peripheral is ascertained to transform message information designated therefor into a digital code which is decodable into an analog baseband signal.

It is another object of the present invention to provide a program for switched communications systems for causing message information designated for a facsimile peripheral to be transformed into a digital code which is decodeable into an analog baseband signal.

It is an additional object of the present invention to provide controller apparatus responsive to a switched communications system for accepting control information and message information from a switching system and for responding to said control information to establish a communications link to a designated facsimile peripheral, to indicate when said communications link has been established and to issue pulsing signals to said designated facsimile peripheral and thereafter for converting said message information into a facsimile format, for transmitting said message information in facsimile format to said designated facsimile peripheral and for subsequently terminating said communications link.

It is a further object of the present invention to provide a program for a switched communications system for recognizing message information designated for a facsimile peripheral, enabling facsimile controller apparatus whenever such recognition occurs, issuing destination information to said facsimile controller apparatus to cause a communications link to be established and issuing said message information to said facsimile cotroller apparatus for transmission.

Various other objects and advantages of the present a switched will become clear from the following detailed description of an exemplary embodiment thereof, and the teleprinter or features will be particularly pointed out in conjunction with the appended claims.

In accordance with the teachings of the present invention aswitched communications system, including store and forward facilities, is provided wherein any of a plurality of teleprinteror teletypewriter peripherals may be given access to the communication system and input information thereto destined for one or more peripherals thereof; input information from a transmitting peripheral is stored under the control of a central switching system which acts to inspect the destination information associated therewith; if a destination peripheral employing facsimile equipment has been designated, facsimile controller means is enabled and destination information associated with the facsimile peripheral defined is provided thereto from said central switching system; in response to said destination information telephone communications to said defined facsimile peripheral is initiated by said facsimile controller means and an indication is provided thereby to said central switching system when a communications link with said defined facsimile peripheral has been established and said defined facsimile periperal is ready to receive facsimile information; phasing information is then exchanged between said facsimile controller means and said defined facsimile peripheral and thereafter stored information destined for the facsimile peripheral defined is transformed into a digital signal capable of being decoded into a baseband signal and applied to said facsimile controller means; the digital signals applied to said facsimile controller means are decoded into a baseband signal which is then transformed into a suitable facsimile format and transmitted to said defined facsimile peripheral; upon transmission of all of the stored information for said defined facsimile peripheral, the communications link established between said facsimile controller means and said defined facsimile peripheral is terminated. The invention will be more clearly understood by reference to the following detailed description thereof in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic diagram illustrating an exemplary embodiment of a switched communications system including a facsimile output terminal in accordance with the teachings of the present invention;

FIG. 2 is a schematic diagram illustrating an exemplary data network in accordance with the teachings of the present invention for the facsimile output terminal of the switched communications system illustrated in FIG. 1;

FIG. 3 is a schematic diagram of an exemplary order register suitable for use in the facsimile output terminal of the switched communications system depicted in FIG. 1;

FIG. 4 is a schematic diagram showing an exemplary ready tone detector circuit suitable for employment in the facsimile output terminal of the switched communications system shown in FIG. 1;

FIG. 5 is a generalized system flow diagram illustrating in a highly simplified manner, data flow through an exemplary switched communications system according to the instant invention when the same is engaged in the transmission of facsimile information;

FIG. 6A and 6B are flow charts setting forth a highly simplified overview of the programs associated with the output operation of the instant invention in a facsimile mode;

FIG. 7 is a flow chart illustrating an exemplary Main Routine program portion for controlling the output operation of the instant invention in a fscsimile mode; and

FIG. 8A - 8J are flow charts illustrating various exemplary branch routines for the Main Routine program portion depicted in FIG. 7.

Referring now to the drawings and more particularly to FIG. 1 thereof, there is shown a schematic diagram of an exemplary embodiment of a switched communications system which includes facsimile output terminal apparatus in accordance with the teachings of the present invention. More particularly, FIG. 1 illustrates a switched communications system including store and forward facilities for message and destination information which may have been received from any of a plurality of remotely located sending peripherals which may take the form of conventional teleprinter or teletypewriter stations. Such sending peripherals are selectively given access to the line as a function of the switching initiated by a control computer which may operate according to a polling or contention arrangement. After a selected sending peripheral has been given access to the line, destination and message information therefrom is transmitted to the central computer where time and date information is appended thereto and the same is stored and the destination information associated therewith is analyzed. Should the destination information analyzed indicate that the desired receiving location is a remotely located teleprinter or teletypwriter peripheral, the designated, remotely located teleprinter or teletypewriter is contacted by the central computer and the stored time, date and message information forwarded thereto as soon as such peripheral becomes available in much the same manner as is achieved in conventional store and forward telegraphy systems. However, should the analysis of the destination information conducted indicate that a facsimile device is the desired destination peripheral, a specialized mode of operation is initiated under program control.

In this specialized mode of operation of the switched communications system according to the present invention, a facsimile controller which is connected to a public and/or private telephone network through a data access arrangement is actuated under program control. The facsimile controller includes conventional facsimile electronics which are compatible with the facsimile apparatus present at the destination peripheral, means for initiating a telephone communication and means for detecting a responsive state at a remotely located facsimile terminal which has been contacted. When the facsimile controller is actuated, the means for initiating a telephone communication is enabled under program control and an attempt is made to establish a communications link to the remotely located facsimile terminal designated. If the attempt to establish a telephone communications link is successful and a designation is received to indicate that the remotely located facsimile terminal is in a condition to receive facsimile information, a ready condition is detected at said facsimile controller and an interrupt is generated in response thereto. The central computer will then return to service the facsimile controller to place the facsimile electronics therein in a send mode so that pushing information is supplied to the facsimile apparatus at the remotely located facsimile terminal designated. Upon the completion of the phasing interval, message information destined for the facsimile terminal is transformed, under software control, into a digital code representative of facsimile information and forwarded to the facsimile controller. As each byte of the digital code is received at the facsimile controller it is encoded into a suitable analog baseband signal and supplied to the facsimile electronics for application to the telephone communications link established in precisely the same manner as would occur were document information being scanned at an individual facsimile device. When all of the message information stored has been forwarded to the facsimile controller, an end of message signal is supplied from the control computer and thereafter stop tone is broadcast by the facsimile controller to the remotely located facsimile peripheral. Upon the expiration of a predetermined interval, the facsimile controller is caused to disconnect the telephone communications link established, under program control, whereupon the facsimile controller is deactivated and the communications system may continue with the further interchange of message information between selected, remotely located peripherals.

Although a specific switched communications system will be described in conjunction with FIG. 1 to acquaint a reader with a preferred embodiment of the present invention, it will be appreciated by those of ordinary skill in the art that one of the principal aspects of the present invention is the provision of a switched teleprinter communications system with the capability to selectively establish communication with and transmit message information in a facsimile format to designated, remotely located peripherals having facsimile apparatus present thereat. For this reason even though an exemplary switched communications system is set forth in its entirety herein, the primary thrust of this application is directed to the techniques, apparatus, methodology and programming requisite to providing a switched teleprinter communications system with the capability to selectively establish communication with and transmit message information which has been transformed into a facsimile format to designated facsimile peripherals. Furthermore, it will be appreciated by those of ordinary skill in the art that the techniques, apparatus, methods and programs disclosed herein as employed to provide a switched teleprinter communicatons system with a capability to selectively establish communication with and transmit message information in a facsimile format to designated facsimile peripherals are fully applicable to other conventional switched teleprinter or teletypewriter communicatons systems without an exercise of inventive skill even though programs and programming and encoding techniques may require modification to fulfill the requirements of particular equipments or system organization or protocols. Accordingly, it will be appreciated that the inventive concepts set forth herein should not be construed as limited to the details of the particular switched teleprinter communications set forth.

The Switched Communications System

The exemplary embodiment of a switched communications system in accordance with the teachings of the present invention schematically illustrated in FIG. 1 comprises a central switching means 1, a common data bus means 2, priority bus means 3, central station storage and monitoring facilities 4-6, teleprinter subcontroller means 7 and facsimile subcontroller means 8. The central switching means 1 may take the form of a conventional digital computer which acts to control all access by remotely located terminals to the switched communications system illustrated in FIG. 1. Although a relatively small scale digital computer providing 4000 16 bit words of storage may be employed as the central switching means 1, a somewhat larger device would ordinarily be preferred to enable the switched communications system as a single entity to control a rather large scale store and forward teleprinter communications system. For this reason the central switching means 1 may take the form of a Sigma 3 or Sigma 5 computer system conventionally available from Xerox Data Systems of El Segundo, Calif. The Sigma 3 or Sigma 5 computer system as indicated in FIG. 1, would include a memory, a central processor (CPU) and an input/output processor (IOP) which may be integral. Typical appropriate memory, central processor and input/output processor configurations for the Sigma 3 or Sigma 5 computer system selected for use as the central switching means 1 are described in detail in the "Xerox Sigma Computer Systems/Interface Design Manual", published by Xerox Data Systems, Vol. No. 900973E, June, 1973. The Sigma 5 computer system is here selected for purposes of discussion and in fact is employed in switched teleprinter communications systems suitable for modification into a switched communications system according to the instant invention, such as the "Tele Net" teleprinter communications system serving the Xerox Corporation, because these computer systems are highly versatile and provide substantial operating advantages over other systems when employed as a line control station for a communications system such as the 85A1 Data Selective Calling System" described in The Bell System Data Communications Technical Reference, published by A T & T. It will be appreciated by those of ordinary skill in the art that although Sigma series systems have here been selected for purposes of discussion, any computer system manifesting appropriate storage and processing capabilities could be employed as the central switching means 1 to act, when apprpriately programmed, as the central switching means 1. However, the selection of Sigma series systems, as will be appreciated by those of ordinary skill in the art does impose certain organizational requirements on the system and hence the configuration of the communications system illustrated in FIG. 1 is tailored to reflect such organizational requirements so that, should an alternate form of central switching means 1 be employed, the system configuration hereinafter described in conjunction with FIG. 1 would be varied to reflect the organizational needs thereof.

The organization of the central switching means 1 is such that when a Sigma system is employed, the memory and interface therefor are characterized by simplicity, high data transfer rates and substantial flexibility. In addition, the central processing unit (CPU) and the input/output processor (IOP) are provided with direct connections to memory so that each processor may carry out functions independently of the other. The input/output processor (IOP) provides lines through which peripheral units are controlled by the central processor (CPU) and is characterized by automatic operation. Following program initiation, data transfers occur automatically and without further direct program intervention unless required for input/output operations. The input/output processor is provided with an interface which consists of data lines, function lines, status lines, control lines for strobes, acknowledgements and the like, priority determination lines, service request lines and miscellaneous lines so that all transactions with external peripheral interfaces are handled therethrough.

The switched communications system illustrated in FIG. 1 is in the exemplary communications system set forth, organized according to a polling arrangement and hence the central switching means 1 periodically polls or invites each peripheral which in this case takes the form of remotely located teleprinter or teletypewriter stations, to send a message. Furthermore, these polling activities may be carried on in a parallel mode to render input or output activity on a given line independent of similar activities on other lines. When a station having message information to be transmitted is ascertained by the central switching means 1, the central switching means 1 acting under program control assigns an input sequence number to the message to be received, develops a time and date stamp therefore and activates the station's transmitter to thereby provide access to the common data bus 2. As the message transmitted is received at the central switching means 1, it is stored in a buffer for the line associated therewith. When the message buffer is full, appropriate forward and backward message links are inserted to provide message chaining among the various portions of each message received and the contents of the buffer are stored on a high speed storage device. These activities are continued by the central switching means 1, acting under program control, until an end of transmission indicator is received from the accessed station. At this point the central switching means 1, acting under program control, causes the message or destination information associated with the received message to be released to an analysis sequence where the destination information contained therein is validated as to format and routing requirements. If the message received is acceptable, an output header is generated under program control to replace the input header and it is placed in an output line queue for the destination peripherals listed in the header. The output line queue is relieved and the message transmitted on a first in first out basis. As each header cycles to the top of the output queue, an attempt is made to access and transmit to the addressed destination peripheral and if such destination peripheral is available in a receive mode, the message stored is forwarded thereto. However, if the designated destination peripheral is unavailable, the message is held until such time as transmission can take place.

The central switching means or, more particularly, the interface of input/output processor (IOP) thereof is connected to the common data bus means 2 and the priority bus means 3. The common data bus means 2 typically comprises three 14 wire cables as described in the "Xerox Sigma Computer Systems/Interface Design Manual", supra and acts as a conduit through which all order and data information, as well as function indicator, acknowledgement, function response, service call, interrupt, end data and end service information, are conveyed. In this manner, the common data bus means 2 provides eight information channels which are available on a time shared basis for conveying information between the central switching means 1 and designated ones of the peripherals connected thereto. Each of the peripherals illustrated for the switched communications system depicted in FIG. 1, as well as the central switching means 1, is connected to the common data bus means 2 in parallel and it is through the common data bus means 2 that central switching means 1 controls the activities of each peripheral in addition to exchanging information therewith in a manner well known to those of ordinary skill in the art.

The priority bus means 3 comprises a cable containing approximately 30 wires which is connected to the input/output processor (IOP) portion of the central switching means and in series to each of the peripherals of communications systems depicted in FIG. 1. The priority arrangement with Sigma series equipment, as is well known to those of ordinary skill in the art, is such that the last serially connected peripheral has priority over those preceding it and hence may gain access to the central switching means 1 to the exclusion of peripherals preceding it in the serial chain associated with the priority bus means 3 in the absence of a higher priority interrupt. On this basis, the facsimile subcontroller means 8 has priority over the teleprinter subcontroller means 7; however, this arrangement is merely a choice of design which may be varied to suit design expediency. Of course, should IBM systems be employed for the control switching means 1, an oppositely ordered priority arrangement would be associated with the priority bus means 3 so that priority is a function of the order of connection. This difference, however, relates to the normally closed character of the priority bus arrangement employed in Sigma series systems and the open arrangement employed with IBM equipments. However, once the choice of the central switching system 1 is made, the nature and character of the common data bus means 2 and the priority bus means 3 would be determined and the connections of peripherals thereto as well as subcontrollers therefor are ascertained. The nature of the priority bus means 3 is fully detailed in the "Xerox Sigma Computer Systems/Interface Design Manual", supra whose contents are incorporated herein by reference; however, for the purposes of the instant disclosure it is sufficient to appreciate that in the case of simultaneous service calls or interrupts for the switched communications system described, the peripheral having highest priority in a closed system would be that connected most remotely in the serial chain from the central switching means 1. In essence, four signals designated HPI, HPS, AVI and AVO may be carried on the priority bus means 3 wherein HPI stands for high priority interrupt, HPS stands for high priority service, AVI stands for available input and AVO stands for available output. The common data bus means 2 and the priority bus means 3 are terminated through impedances Z.sub.1 and Z.sub.2 to ground as shown in FIG. 1. As both the common data bus means 2 and the priority bus means 3 may be considered to be 33 ohm cables, impedances Z.sub.1 and Z.sub.2 may be 33 ohm resistors so that each cable is terminated by its characteristic impedance.

The central station storage and monitoring facilities may comprise, as shown in FIG. 1, a controller and high speed storage means 4, central station line print monitoring means 5 and bulk storage controller and media means 6. The controller and high speed storage means 4 may take the form of a Model 7201 RAD controller and a plurality of Model 7204, 3.0 MB RAD each of which is available from Xerox Data Systems. The 3.0 MB RAD or Rapid Address Devices, well known to those of ordinary skill in the art, are high speed, fixed head disc storage devices which store information in designated address locations, defined in terms of a track number and sector. Each RAD is capable of storage for up to 3 megabytes wherein storage is arranged in 512 tracks, each track containing sixteen sectors each of which is capable of holding 360 bytes. In a typical embodiment of the instant invention three RAD units were employed. The Model 7201 RAD controller is connected intermediate the plurality of RAD units and the common data bus means 2 and is employed to interface, in the well-known manner, the plurality of Model 7204 RAD units with the common data bus means 2 and the priority bus means 3 so that information may be taken from the common data bus means 2 and placed in storage for subsequent modification and forwarding. The RAD controller acts, in essence, to provide queueing by device before and after input/output execution exits, error recovery and automatic flip-flop between RAD units in allocating and accessing file space. The controller and high speed storage means 4 is employed at the central station to provide the switched communications system depicted in FIG. 1 with a store and forward capability as well as being relied upon to establish a message queue for the central switching means 1. Additionally, infrequently utilized programs may be stored on the RAD and periodically fetched by a nonresident program controller.

It will be recalled from the brief description of the operation of the central switching means 1, set forth above, that as each character is transmitted by a sending peripheral it is loaded into a buffer at the central switching means 1 associated with that line and when the buffer is full, appropriate backward and forward links are inserted to chain each message together and then the contents of the buffer are logged on a RAD and this activity continues until an end of transmission indicator is received. Thus, any message transmitted within the switched communication system depicted in FIG. 1 is initially logged on the RAD together with the destination information, in the form of an input header, forwarded therewith. At this point, the header information is released to header analysis where, under program control, an output header is generated to replace the input header and such output header is placed in the output line queue for the destination peripherals listed in the header. More particularly, if a single destination is specified, the output header is employed to replace the first sector of the message logged on the RAD which contained the input header. Similarly in multicharacter messages, an output header plus enough message information to fill a sector on the RAD is generated and recorded on the RAD for each destination peripheral with one destination peripheral header being employed to replace the input header. If the message information exceeds the storage available in one sector on the RAD, the remainder of such message information is stored in a second sector to which all output sectors are threaded or linked. In addition, all output headers are threaded one to the other to establish a desired message queue which is then relieved on a first in first out basis. Thus in this manner the controller and high speed storage means 4 is employed at the central station to provide the switched communications system depicted in FIG. 1 with a store and forward capability in addition to being utilized to form the message queue for the central switching means 1.

The central station line print monitoring means 5 may comprise one or more conventional line printer units, such as a Model 7440 line printer, available from Xerox Data Systems and is employed at the central station to monitor through printing and operator inspection all information conveyed through the switched communications system depicted in FIG. 1. The function of the central station line print monitoring means 5 is to print all message information forwarded to the central switching means 1 and all information forwarded therefrom so that the operation of the system as a whole may be reviewed or inspected at any time by an operator to assure appropriate transmission is taking place. In addition, though not illustrated in FIG. 1, a central location may be provided with teleprinter or teletypewriter apparatus whose principal function is to monitor transmissions from certain peripherals whose operation and/or leased line communications links are continuously suspect. Furthermore, additional teleprinter or teletypewriter apparatus may be employed to complement the action of the line printer monitoring means 5 to provide multiple inspection sites at a central location; however, this redundancy in apparatus may be avoided by the designation of the central station as a teleprinter or teletypewriter peripheral. The central station line print monitoring means 5 is connected in parallel to the common data bus means 2 and in series to the priority bus means 3.

The bulk storage controller and media means 6 may comprise a Model 1320 Tape Control unit and a plurality of Model 7322 Tape Units which are available from Xerox Data Systems, employ nine tracks and exhibit a bit density for storage purposes of eight hundred bits per inch (800 bpi). The Model 7320 Tape Control unit is connected intermediate the plurality of Model 7322 Tape Units and the common data bus means 2 and the priority bus means 3 so as to serve as an interface therefor whose operation is controlled by the central switching means 1 acting under program control. The function of the bulk storage controller and media means 6 is to act as a mass storage device for the switched communications system depicted in FIG. 1 for storage of such data as may be designated as overflow from RAD devices during the course of daily operation and to provide short term message files for subsequent retrieval. For instance, in the exemplary embodiment of the switched communications system depicted in FIG. 1, message information together with destination headers recorded on the RAD devices may be routinely transferred to the bulk storage controller and media means 6 at the termination of a given period of operation such as a day or 72 hours for retention for a designated interval of time such as a three, twenty or thirty day period. During this interval of time, the message information will be available for retransmission or look up at the central station through a designation of date, time and destination or sequence and destination information associated with a desired message. After an expiration of the designated interval of time, the message tapes may be erased for reuse or removed and placed in storage for a further period.

The teleprinter subcontroller means 7 may comprise a conventional communications controller device such as a Model 7611 Communications Controller, available from Xerox Data Systems. The teleprinter subcontroller means 7 acts within the switched communications system depicted in FIG. 1 as an interface between the common data bus means 2 and a leased line TTY communications system 9 wherein access to the common data bus means 2 is provided through operation of the priority bus means 3 in response to a requirement at the central switching means 1 that message information be transmitted to a designated teleprinter or teletypewriter peripheral within the leased line TTY communications system 9 or conversely in a response by the central switching means 1 to an interrupt or a service request following polling, generated at the teleprinter subcontroller means 7 reflecting a transmission requirement at a teleprinter or teletypewriter within the leased line TTY communications system 9. The Model 7611 Communications Controller, as well known to those of ordinary skill in the art, may accommodate up to 64 leased telephone lines or the like having data conveyancing speeds ranging up to 1800 baud; however, in the Tele-Net system presently in place only 18 to 22 110 baud, half-duplex circuits are relied upon in the leased line TTY communications system even though the present Tele-Net system is designed for expansion to support a full controller complement of 64 lines. In brief, the teleprinter subcontroller means 7 is associated with only a single data channel within the common data bus means 2, as defined on a real time basis as aforesaid, and acts, in response to commands issued by the central switching means 1, to establish communication between the common data bus means 2 and a requesting or designated teleprinter or teletypewriter peripheral by simulating the action of a multiplexer serving each communications circuit connected thereto as though it resided on a dedicated input/output line or circuit. In addition, specialized programming devoted to the teleprinter subcontroller means 7 may act within the central switching means 1 to perform an ASCII to EBCDIC conversion and priority check for message information transmitted from an actuated teleprinter or teletypewriter peripheral to the common data bus means 2 while an opposite conversion is performed for message information translated through the teleprinter subcontroller means 7 from the common data bus means 2 to a designated teleprinter peripheral. Other than for these functions and establishing the necessary protocols for the communications peripheral as well as the setting of appropriate flags for service requests and the like, the teleprinter subcontroller means 7 appears to a teleprinter or teletypewriter terminal as a device which provides it with appropriate access to the common data bus means 2 and hence to central switching means 1 and thereafter turns transparent for the purposes of data flow between the common data bus means 2 and the requesting or designated teleprinter or teletypewriter peripheral.

The leased line TTY communications system 9 may take the form of a conventional multi-line TTY communications system wherein each line is a dedicated, multi-point facility with a substantial number of peripheral terminals connected to each line or circuit. Each TTY peripheral terminal may take the form of a 33 ASR or 35 ASR teletypewriter for example although various other terminal configurations such as a Univac DCT 500, a Memorex 1240 or 1280, a Bell and Howell Optical Mark Reader or CRT's as available from Hazeltine or Datapoint may be employed. A suitable, conventional leased line TTY communications system such as the 85A1 Data Selective Calling System may be employed for the leased line TTY communications system 9. This system is described in Bell System Data Communication Technical Reference published by The American Telephone & Telegraph Co., entitled "85A1 Data Selective Calling System," dated April 1968, whose disclosure is incorporated by reference herein, and it will be appreciated by those of ordinary skill in the art that the central switching means 1 together with the common data bus and priority bus means 2 and 3, the central station storage and monitoring facilities 4 and 6 and the subcontroller means 7 form a store and forward station controller or line control station for the calling system described therein. In essence, the 85A1 Data Selective Calling System is a leased or private line selective calling system wherein each of a plurality of communications lines may be connected through various hubbing points to a plurality of remote stations which here take the form of teletypewriter or teleprinter peripherals. Thus, for instance, in the "Tele-Net" System presently serving the Xerox Corporation, twenty half-duplex circuits or lines may be connected to the teleprinter subcontroller means 7 and 175 33 ASR or 35 ASR teletypewriter or teleprinter peripheral terminals are connected thereto to thereby establish a store and forward communications system which serves the needs of this corporation on an international scale. This inplace switched communications system has an average message volume of 5000 transactions per day with the average message consisting of 600 characters and is readily expandable to 300,000 messages per 16 hour day for the single port network shown, while further expansion to a multiport facility is available.

The employment of the 85A1 Data Selective Calling System for the leased line TTY communications system 9 is highly advantageous because at each remote peripheral station the teleprinter terminal serves as the source and sync for message information signals while the station control unit serves as the source and sync for administrative information. The teletypewriter per se is therefore not actively concerned with the logical organization of the station but merely provides the stimuli regarding traffic-to-send and ready-to-receive conditions required by the station control unit. The station control unit thereby includes all of the character detection and generation capability required along with appropriate logic to complement the on-line administrative procedures of the system. This form of organization is highly advantageous because the separation of the message generation and receiving functions from the control renders the organization of each terminal highly flexible. Furthermore, the utilization of either 33 or 35 ASR teletypewriter means is highly advantageous because messages may be prepared off-line to await system pickup through polling while a receiving capability is not prohibited during actual message preparation, a familiar keyboard arrangement is provided for operator convenience, data handling rates or throughput is substantially increased over "Telex" hardware and operator time is not wasted by a requirement that contact within the system be manually initiated as through a dialing arrangement or the like. Thus, it is typical of the leased line TTY communications system 9 when the same is viewed as configured along the lines of the 85A1 Data Selective Calling System that a plurality of teleprinter or teletypewriter peripheral terminals may be connected to each of the leased line communication circuits connected to the teleprinter subcontroller means 7 and an individual one or more of such teleprinter or teletypewriter terminals selectively placed in communication with the common data bus means 2.

Teleprinter Communications

The portion of the exemplary switched communications system depicted in FIG. 1 which has thus far been described in essence forms the switched store and forward teleprinter communications system which is known as "Tele-Net" and presently serves the Xerox Corporation on international and domestic levels. A printout of an appropriate program for a Sigma 5 computer, employed as the central switching means 1 for the portion of the switched communication heretofore described, is appended hereto as Appendix A to provide a complete disclosure of this portion of the switched communications system depicted in FIG. 1. However, as the switched store and forward teleprinter communications system known as "Tele-Net" merely comprises a known portion of the combination upon which the instant invention proceeds, a detailed description of the program for enabling this portion of the overall system is not set forth as the same would be apparent to one of ordinary skill in the art. Furthermore, in the interests of conciseness and reader convenience, the operation of the portion of the switched communications system depicted in FIG. 1 which comprises "Tele-Net" or the store and forward teleprinter communications system per se will be briefly summarized at this juncture of the specification prior to a description of the facsimile subcontroller means 8 and the apparatus connected thereto. This mode of disclosure is here adopted because the instant invention depends upon and acts in combination with a switched teleprinter communications sytem and hence a basic understanding thereof serves as a useful predicate for the remaining subject matter set forth in the instant specification. However, it will be appreciated by those of ordinary skill in the art, that the instant invention does not depend upon the details of a specific switched store and forward teleprinter communications system and hence the switched store and forward teleprinter communications system set forth may be readily modified without the exercise of inventive skill and/or reconfigured to support other than Sigma system central switching means. Furthermore, should other than Sigma system central switching means be relied upon, appropriate programming material may be developed by appropriate modification of the program set forth in Appendix A, supra through language modification within the scope of conventional programming techniques or available on an automatic basis through the use of compiler apparatus.

Briefly, the switched store and forward teleprinter communications system within the exemplary switched communications system depicted in FIG. 1 operates, when otherwise unoccupied, to poll remotely located teleprinter peripheral terminals connected within the leased line TTY communications system 9 to various ones of the plurality of leased telephone or communications circuit inputs applied to the teleprinter subcontroller means 7 and thereby ascertain if a message is to be transmitted. Thus each communications circuit within the leased line TTY communications system 9 terminates in the teleprinter subcontroller means 7 and each communications circuit so terminated has one or more teleprinter or teletypewriter peripheral terminals connected thereto. The central switching means 1 polls each peripheral terminal in the system on a periodic basis as part of the overall line control function exercised thereby under program control, to ascertain whether or not a message is ready to be sent. This activity is carried on in a parallel manner on each communications circuit so that input or output on a given line is independent of activity on any other line. All information conveyed through the teleprinter subcontroller means 7 is buffered into memory through one of the common 8 bit input/output channels of the eight channels available within the common data bus means 2. A direct input/output interface (not shown) associated with the central switching means 1 may be relied upon for output purposes so that input and output operations conducted by the central switching means 1 are rendered independent in nature. The input and output operations at the central switching means 1 are driven by a pair of adjacent external interrupts with the receive interrupt being of higher priority than the transmit interrupt.

The polling function initiated by the central switching means 1 is only a small part of the line control function exercised thereby under program control and it will be appreciated by those of ordinary skill in the art that polling takes place only after a plurality of other conditions have been satisfied. More particularly the responsibilities of the line control exercised by the central switching means 1 includes a send or receive determination for each line, the initiation of appropriate send or receive action either by addressing or polling, acting to receive and log or read and transmit the messages received or the program generated, the requesting of header analysis at appropriate times, the maintenance of statistics regarding line and terminal peripheral activity and the generation of appropriate responses upon the receipt of information indicative of line, terminal peripheral, or control unit malfunction or service requests. The exercise of line control functions are divided into two areas which comprise line scanning and line operations. The most important purpose of line scan is to detect idle lines. Three conditions must be satisfied before any normal activity may be initiated by the line scan. These conditions are the line must be up (operative), the line must be idle, and the line must not have any outstanding error conditions. If an idle line is detected during line scan, a determination is made as to whether to send or poll and then shifting to the appropriate operation routine takes place. The choice of whether to send (address) or poll is made during line scan by a testing of the translate/receive bit associated with each line and this is accomplished by the operation routines. A secondary purpose of line scan is to detect service requests for a line and to request header analysis, which takes place either at the reception of the end of transmission indicator or after a predetermined number of message segments have been received and detected.

The line operations area includes the functions of polling, addressing, header analysis, relieval/retrieval, file management, etc. The polling operation, when enabled for a line, commences and continues until all terminals on a line have been polled to limit for exhaustion. Polling is accomplished by establishing a polling list in the form of a terminal peripheral index arranged by line. The terminal peripheral being polled is noted through a pointer arrangement and the count is incremented after the number of messages received reaches the polling limit or the terminal responds with a no-traffic response. After polling for the last terminal peripheral is completed for a given line, the pointer is reset so that a new polling cycle may be initiated. Polling and response requires several character times and the completion thereof is indicated by an interrupt.

In the store and forward teletype portion of the switched communications system, output queues established on the RAD means within the controller and high speed storage means 4 are arranged by line under program control. Therefore, terminal peripheral address information will not be available to an address routine until destination header information has been read from the RAD unit. For this reason actual addressing in a line operation is not done until after such header information has been read from the RAD. The address information from the output header is saved for possible error conditions and for normal traffic, the line queue is updated with the chaining address in the header segment. If the terminal is indicated as being down, no messages will be sent to it. In addition, if a down terminal does not have intercepted traffic indicated, a terminal trouble overlay may be enabled to start intercept.

Header analysis functions on a system basis processing headers from the queue on a first in first out basis. Header analysis is not performed in synchronization with line control on a per line basis but reads input headers from the RAD units into a work area. As the input header information is analyzed under program control, output header information is created in an output work area and is then written onto a RAD unit in a pre-assigned location which forms the output queue for the destination line. The RAD location of the input header is then free for reuse. One of the functions of the line control is to scan the queues established for output lines and to initiate transmission if a line is idle and a message queue has been established for that line. If addressing is successful, the message will be sent by first translating the output header segment followed by each text segment associated therewith. The output queue is updated to reflect that the message was sent, but the message stored on the RAD unit is retained as a log and may be subsequently retrieved if desirable.

Relieval and retrieval programs are employed when messages which are already logged in a prior chain on a RAD unit must be transmitted. Relieval is employed to permit message information designated for a down terminal peripheral to be saved and later sent when the defined terminal peripheral becomes operative. Retrieval allows access to any message logged on the RAD for conditions such as when a destination terminal peripheral requests the retransmission of a previously forwarded message. Relieval is necessary because in a switched, store and forward teleprinter communications system, traffic cannot be halted for other terminal peripherals on the same line as a down terminal peripheral. For this reason the line queue controls must be able to skip over messages for a disabled terminal peripheral. To achieve this function, traffic for a down terminal peripheral is intercepted by retaining the RAD unit address for the next output message for that terminal peripheral. Subsequently, when the down terminal peripheral is restored to normal operations, this address may be employed by the relieval program to locate all messages waiting to be sent to that terminal peripheral. This is possible because even after a message is removed from an output queue, it remains chained to the same messages as when it was queued, in that once an output header is established, it remains a fixed link in the chain attached to the output line so that the relieval program merely has to forward scan the chain established looking for messages pertaining to the terminal peripheral after relieval until it catches up with the line queue controls. Under the retrieval program access to any message logged on a RAD unit is available and any message may be retrieved to any terminal; however, because of the significant impact upon overall system performance and integrity, all requests for retrieval must be made by supervisor console order. Message retransmissions under retrieval may be requested by specifying the original destination and sequence number. The retrieval program locates the designated message by first locating the last message placed into the appropriate output queue of the designated line. The chaining address in the header segment of this message is then employed to backward scan the chain until the requested message is found. If more than one message is specified, a chain is scanned backward until all the messages are set so that messages are retrieved in a reverse or a last in, first out order.

File arrangement within the switched store and forward teleprinter communications system is such that files are maintained in a manner to enable messages to be placed in queues if the destination lines are busy handling previous messages or are otherwise unable to accept traffic. Retransmission of all messages is made possible by uniquely identifying each message. To render file management highly efficient, messages are logged in sequence of 360 bytes to conform with the sector size of the RAD units. Thus, a message 600 characters in length will occupy two message segments on the RAD unit; however, the segments of a message need not occupy adjacent sectors on the RAD units. A routine in the main body program controls the dynamic allocation of sectors on the RAD units. Operating upon all of the parallel connected communications lines connected to the teleprinter subcontroller means 7, this program assigns a sector to a message segment that has not been written upon. Sector allocation on the RAD units is a sequential operation and message logging is essentially random in nature. If a message segment cannot be logged on an assigned sector, an override function is performed and a new sector assigned. To link the various segments of a logged message together, a chaining technique is employed. The header of a message contains the RAD unit address of the first segment of the text and each text segment is chained to the next logical text segment. These chaining addresses are inserted into the control field of each record by header analysis. Each header contains the RAD address of the next and previous header in the same queue to thus achieve complete forward and backward chaining. All output headers are formed on a line basis and when a multiple destination addressed message is received, one output header is created for each destination address and is logged in the appropriate line queue. The message text need be logged only once as each of the associated output headers in the respective line queues contains the RAD unit address of the same first text segment. Various error overlay and check point programs may also be included for additional line operations.

Returning now to the discussion of the polling activity carried out by the central switching means 1 on a periodic basis and in parallel on each communications line connected to the teleprinter subcontroller means 7, it will be appreciated that if a terminal peripheral has message information to send, the central switching means 1 assigns an input sequence number
Other info:


Inventors: Vieri, Bruno (Dallas, TX, US)

Application Number: 456201
Filing Date: 1974-03-29
Publication_date: 1976-05-18
Assignee: Xerox Corporation (Stamford, CT)
Primary Class(es): 379/100.13 178/3, 178/30, 341/138, 358/407, 358/435, 358/440, 379/100.09
Other Classes:
US Patent Ref:

3337686	Aug, 1967	Grant et al.	178/26.
3631455	Dec, 1971	Gregg	340/324.
3751582	Aug, 1973	Wernikoff et al.	178/6.
3869571	Mar, 1975	Delavie	178/30.

Other Refs:
Primary Examiner: Robinson, Thomas A.
Assistant Examiner:
Attorney: