GB2095076A - Method and apparatus for maximizing voice and data transmissions in a multi line system - Google Patents

Abstract

Methods and apparatus for maximizing voice and data transmission in a multiline system are presented. In accordance with the method, multiple data channels are in effect multiplexed onto a single voice channel, the number of such data channels being multiplexed onto the voice channel depending upon the maximum data rate of the digital devices coupled thereto. In this manner a substantial number of phone lines coupled to a PBX type switching system may be used for communication to and from terminal and other digital devices without the sacrifice of any substantial voice line switching capacity of the system, and more particularly, without sacrificing voice line switching capacity on a one for one basis.

Description

SPECIFICATION Method and apparatus for maximizing voice and data transmissions in a multiline system 1. Field of the invention The present invention relates to the field of multiline switching systems, and more particularly, to systems for the switching of voice and data lines and/or the switching of data lines characterized by differing expected data rates.

2. Prior art Telephone switching systems, of course, are well known in the prior art, and generally fall into two categories, specifically central office switching systems and PBX systems. Since the present invention is particularly directed to PBX systems or PBX type systems, only the relevant prior art relating thereto will be described.

PBX systems are systems generally intended to be used within a given office, plant or other facility to provide the required phone line switching to route calls within the facility without coupling to the phone company trunk lines, and to couple the phone lines within the facility to the trunk lines as required to handle incoming and outgoing calls. Initially, such systems were plug board systems wherein an attendant manually completed the circuits as required using patch cords associated with the trunk lines. As dial features were implemented, electromechanical techniques were implemented which enabled internal stations to dial each other or to gain access to trunk lines without attendant intervention, though incoming calls were still handled by the attendant.The newer PBXs generally incorporated electronic switching methods as a replacement for the electromechanical switching devices to provide more flexibility, reliability and lower costs. In general however, such systems still utilized one switch for each phone connection so that rather large electronic systems were required for the routing of calls within all but the smaller facilities.

To reduce the number of switches required, techniques have been used to effectively multiplex the switching task so that a lesser number of switches or even a single switch may be used to simultaneously establish and maintain a number of phone line connections within the facility serviced by the PBX. At least two such systems are currently being offered, both of which are described below.

Rolm Corporation, assignee of the present invention, manufactures various types of computer controlled PBXs, which it refers to as CBXs. One such system is their VLCBX, a medium size system which will support up to 4,000 telephones. In this system, each voice signal is sampled 12,000 times per second and each sample is converted into a 12 bit parallel digital signal. A time division multiplex bus is used comprising three buses, the first being a 1 6 bit data bus (four bits of which are floating during data transmission, but which are used during some time periods for purposes other than data transmission), a 14 bit source bus, referred to as ABO, and a 14 bit destination bus, referred to AB1. The source bus as well as the destination bus are effectively both address buses.

The phones in the system are coupled to interface cards referred to as CODECS, 1 6 to a card, which provide the analog to digital conversion and digital to analog conversion functions to communicate on the data bus. The CODECS have a unique address for the transmit and receive function of each phone coupled thereto. These CODECS are coupled to the source bus, the destination bus and the data bus, so that when any of the phones coupled to the CODEC are addressed by the source bus, it will put the digital data for that phone onto the data bus, and when any phone coupled thereto is addressed on the destination bus, it will receive data from the data bus and convert it to analog for the addressed "receiving" phone.A controller maintains a connection table, cycling through the connection table every 83 microseconds (i.e., 12,000 times per second) so that all calls may be handled on the time division multiplexed basis.

In addition to cycling through the connection table, part of the time is devoted to detecting a change of conditions by a computer or processing unit (CPU) so that the connection table can be updated or some special function may be instituted, such as a ring signal. (There are of course other boards coupled to the bus, such as tone generators, etc. not relevant to the present discussion.) In essence, the connection between two telephones is established in this system by -appropriate address entries into the connection table so that on each pass therethrough, the data from one phone is placed on the data bus and received by the second, and subsequently on the same pass, the data from the second phone is placed on the data bus and received by the first phone.Thus, the bilateral communication between the two phones is established as a result of the addresses in the connection table at a rate of 12,000 per second, the table itself being updated as a result of a change of conditions (off hook, on hook, etc.) on a much slower basis.

The 1 2 kHz sampling rate not only provides excellent voice reproduction in the analog to digital and subsequent digital to analog conversion, but also is sufficiently high for good digital data communication, whether comprising a pure digital signal (i.e., high level-low level signals) or coded signals such as, by way of example, frequency shift keyed signals, as digital communication techniques and coding schemes intended for use over phone lines generally recognize the limited bandwidth of substantially all phone systems. Thus, the phone system within any facility may be used to couple digital devices and systems together such as, by way of example, terminals to one or more central processing units, etc., thereby providing a highly flexible and versatile data communication system, as well as voice communication system.However, such use of prior art phone systems, whether of the foregoing type or any other type, provides a heavy load on the switching system, severely cutting into the voice line switching capacity. In particular, while a switching capacity of 1 50 connections will support 800 telephones in the MCBX because of the fact that most telephones are only used a small fraction of the day, terminals are frequently used most of the day, so that the switching capacitity of the PBX for voice communication may go down almost on a onefor-one basis for each terminal in the system, severely limiting the practical use of ordinary phone systems for data communication.

Another prior art switching system which utilizes analog to digital and digital to analog conversion, so that switching may be accomplished in the digital realm, is the SL-1 system of Northern Telecom, Inc. That system uses a serial data bus, rather than the parallel bus of the Rolm system, so that the digitized data appears serially on the line. Consequently, the time of communication of each digitized sample is ionger so that fewer calls may be handled by this single line. The system is expandable upward however, by merely incorporating additional bus lines and providing apparatus for handling communication between bus lines. Again, such system may be used for digital communication, though at great expense to the switching capacity of the voice carrying lines.

Brief summary of the invention Methods and apparatus for maximizing voice and data transmission in a multiline system are presented. In accordance with the method, multiple data channels can share the capacity of a voice channel, yet each data channel is controlled independently of voice control mechanisms and with mechanisms appropriate to its nature. No constraints appropriate to a voice channel are applied, and constraints imposed by the communication channel are applied equally to both data and voice. The number of such data channels is being multiplexed onto the voice channel depends upon the maximum data rate of the digital devices coupled thereto.In this manner a substantial number of phone lines coupled to a PBX type switching system may be used for communication to and from terminals and other digital devices without the sacrifice of any substantial voice line switching capacity of the system, and more particularly, without sacrificing voice line switching capacity on a one for one basis. Various embodiments and techniques are disclosed.

Brief description of the drawings Figures 1 through 3 are diagrams illustrating the prior art CBX switching system.

Figure 4 is a controller connection table illustrating one embodiment of the present invention, as applied to the prior art CBX system.

Figure 5 is a block diagram illustrating one method of implementation of the table of Figure 4.

Figure 6 is a block diagram illustrating the connection and function of the data terminal interface and data line interface of one embodiment of the present invention.

Figures 7a and 7b illustrate two possible forms of the data line interface.

Figures 8a and 8b illustrate the general form of the controller connection table for the embodiment of Figures 4 through 6, and for a still further alternate embodiment respectively.

Figure 9 is a block diagram illustrating one technique for implementing the embodiment illustrated with respect to Figure 8b.

Figure 10 is a block diagram illustrating an alternate method of implementing the invention illustrated in Figure 8b and extensions thereof.

Detailed description of the invention The present invention allows data communication over phone lines coupled to a PBX system in a manner which does not burden the switching capacity of the PBX on a one-forone basis for each data line connection made therein. Thus, a relatively large number of data terminals may be coupled to the phone system for communication with processors, etc., without substantial reduction in the switching capacity of the PBX.

For purposes of illustration of the invention, a specific application of the invention to the VLCBX will be described. Portions of the VLCBX which are relevant to the present invention are illustrated in Figures 1 through 3. In general, a CPU controls the controller, which in turn controls the information on the source and destination buses, and in some instances, the data bus. As previously mentioned, the source and destination buses are 14 bit parallel buses, referred to ABO and AB1 respectively, and the data bus is a 16 bit parallel time division multiplexed bus. Coupled to these buses are a plurality of CODECS, each CODEC and two associated interface cards supporting up to 16 phones. The general organization of the CODECS and interface cards as a functional unit may be seen in Figure 2. Each unit provides four basic functions. These are (i) the code function, whereby the analog signal from each phone coupled thereto may be sampled at the rate of 1 2 kHz and converted to a 12 bit digital signal, (ii) the decode function, whereby the 12 bit digital signal on the data bus may be reconverted to analog, (iii) an off-hook signal communication function and (iv) a ring signal generator. From a system viewpoint, each of these four functions for each telephone set on the system has a separate address so that any of these four functions for any set coupled to the CBX is separately addressable (i.e. put data on the bus, take data off the bus, signal the phone is off hook, generate a ring signal to the phone).The off-hook function merely outputs a single bit for each phone and as such, is a control function signal which is sampled at a much lower rate than the 12 kHz of the voice communication signals. Similarly, the ring signal function merely responds to a single bit to initiate the ring function so that it, too, need not be serviced at the 12 kHz rate.

The controller connection table for the system may generally be seen in Figure 3. This connection table is stored in a dual port random access memory and sequentially addressed through an appropriate sequencer at the rate of 83 microseconds per pass through the table. The 83 microseconds is broken down into 384 time slots, each time slot having an associated memory address. Further, the memory is organized so as to be capable of storing a 14 bit source address and a 14 bit destination address, which will be coupled to buses ABO and AB1 respectively, when that memory location is addressed.Of the 384 time slots, eight are reserved for other control and servicing functions, so that only 376 are available for servicing phone connections. (The reserved eight time slots allow for functions such as poling all telephones for on/off hook information to initiate dialing, breaking connection, etc., functions not altered by the present invention.) Also illustrated in Figure 3 is a possible sequence for establishing a telephone connection between telephone A and telephone B. In particular, the address of telephone A is stored in the source bus location for time slot 2 and in the destination bus location for time slot 5, with the address of telephone B being stored in the source bus memory location for time slot 4 and in the destination bus location for time slot 3.Thus during each scan through the controller connection table for so long as this information remains in the connection table, telephone A will be addressed in the second time slot, thereby telling the CODEC associated therewith to place the 1 2 bit digitized signal of telephone A onto the data bus, with time slot 3 directing the CODEC for telephone B to receive the 1 2 bit digitized signal and reconvert to analog for telephone B. (The time delay of one (or more) time slot between the addressing of A as a source and B as a destination is part of the system protocol which again is not particularly relevant to the present invention.) Thus, in time slots 2 and 3, communication is established between telephones A and B, with telephone A being the source of the transmitted information and telephone B being the destination.Bilateral communication is completed in time slots 4 and 5 in this example, with telephone B being identified as the source and telephone A as the destination. (The protocol of the system allows the specification of both a source and destination address in any one given time slot, though not to provide a connection between the source and destination stated in that one time slot, i.e., if a destination address were provided in time slot 4 in the example of Figure 3, it would not identify the phone which would respond to the signal from the B telephone identified as the source in that same time slot, but instead would respond to the signal from the phone identified as the source in time slot 3, which is empty or blank in this example.) Since the digital information being carried by the data bus is 12 bit digital information, repeated 12,000 times per second, the data bus communication rate for any phone line connection is 144 K bits per second. On the other hand, most data devices have a much lower maximum rate. By way of example, most data devices have some specified maximum transmission rate of bits per second (BAUD) of 300 to 9,600 BAUD, depending upon the device.

Thus, even for a 9,600 BAUD terminal communicating with a central processing unit over one of the phone lines, only one-fifteenth of the 144 k BAUD capability of the CBX is used for that communication, though the voice line switching capability of the system has been reduced by one because of the data line connection. Accordingly, in the present invention, data communication is handled by further multiplexing so that the "sample rate" for data communication is reduced so as to allow the establishment of more data communication connections without a one.-for-one reduction in the voice connection capability of the CBX.

To illustrate the concept, if someone desires to operate a 9.6 k BAUD terminal over one of the phone lines, assuming the data is organized in 8 bit byes, data will be presented for communication at the rate of 1,200 times per second. Consequently, rather than having to "sample" the data each time through the connection table (i.e. 12,000 times per second), one needs only to look for data on that phone connection 1,200 times per second, or on each tenth pass through the connection table.

Thus, on the other nine passes, communication could be established with nine other 9.6 k BAUD terminals without consuming any additional time slots in the connection table, and thus not further diminishing the connection capacity of the switching system. The net result is that ten terminals may communicate through the CBX, while only diminishing the voice communication capacity by the actual use of the ten terminals by one. Note also that since the data bus is a 1 6 bit bus, the bus has the capability of transmitting not only the eight bit byte of data during any "sample", but also other information such as a data valid bit and a parity bit, or for that matter, a larger digital word.

Now referring to Figure 4, a controller connection table illustrative of the present invention may be seen. In this example, there are 384 time slots, the last eight of which are reserved, as in the controller connection table illustrated in Figure 3. Also, as in Figure 3, the first 372 time slots (memory locations) have the capacity of storing one source address and one destination address which are put out on the respective buses on each pass through the connection table. However, the memory locations corresponding to time slots 373 through 376 have the capacity of storing 10 source-destination addresses or designations, of which each source-destination combination are separately addressable. Thus on the first pass through the connection table, the sourcedestination addresses in the first column are put out on buses ABO and AB1 in the normal manner.

Similarly, on the second pass, addresses in column one for time slots 1 through 372 and time slots 377 through 384 are put out on buses ABO and AB 1. However, for time slots 373 through 376, the source-destination addresses in column two are used instead of those in column one.

Thus, as illustrated in Figure 4, the second pass is through the addresses in column one for the first 372 time slots, through the addresses in column two for time slots 373 through 376, and then back through the addresses in the first column for time slots 377 through 384. On each subsequent pass, for time slots 373 through 376, the sourcedestination addresses put out on buses ABO and AB1 come from the next adjacent column, ending on the tenth pass by putting out the sourcedestination addresses in the tenth column. In this manner, the first 372 time slot memory locations, as well as the last eight, are scanned every 83 microseconds as hereinbefore described, fully preserving the function of the first 372 time slots for voice communication and the last eight for their prior art functions.However, each of time slots 373 through 376 may contain up to ten source-destination address combinations, each of which will be sampled, not on every pass or in every 83 microseconds, but which will be sampled every tenth pass or every 830 microseconds, resulting in 1,200 data transfers per second of eight bits (or more) each to provide the 9,600 bit per second communication requirement for the example being discussed.

Potentially in this example, time slots 373 through 376 provide a capacity of storing 40 source-destination address combinations to establish 20 bidirectional data communication connections (as illustrated with respect to Figure 3, a bidirectional connection requires two source and two destination designations). In practice this number is reduced because of the particular protocol, specifically the delay between a source address and a destination address as illustrated with respect to Figure 3, which means that time slot 373 can only provide source address designations, and time slot 376 can only provide designation addresses.Because of this limitation of the system in which the present invention has been incorporated, time slots 373 through 376 in the example of Figure 4 may only contain sourcedestinations to establish 1 5 bidirectional data connections. It will be noted however, that those 1 5 bidirectional data connections were made with the sacrifice of only four time slots for data communication, representing a voice connection capability sacrifice of only two. Further, on examination of this example, it may readily be seen that the sacrifice of the first voice connection for data communication allows up to five data connections, with each subsequent voice connection sacrifice providing a potential of up to ten more data line connections.Further, expanding the concept to lower speed devices, even greater numbers of data devices may be accommodated with this technique. By way of example, a 1,200 BAUD device need only be sampled one-eighth as fast as the 9,600 BAUD device used in the original example, so that theoretically, the time slots devoted to the establishment of data communication connections for such devices could be 80 sourcedestination designations wide, and the sacrifice of only a single voice connection capability would allow communication by 40 such data devices, with the sacrifice of each additional voice connection allowing eighty 1 ,200 BAUD data devices to communicate through the phone system. Furthermore, the concept may be extended to multiplex more time slots than simply 373 through 376 inclusive.The ratio of multiplexed time slots to standard time slots may be fixed permanently by an implementation or adjustable for each specific system depending on the end use configuration.

Having described the basic concept of the present invention, the manner of implementation thereof will now be presented. While implementation may take a variety of forms, the preferred implementation may be seen in Figure 5. In this implementation, the CPU is coupled to a random access memory in the controller which, in one particular embodiment, is organized as a 1024 by 32 bit memory. Actually, as may be seen, a 1024 by 28 memory would be adequate, as the source-destination designations represent two 14 bit numbers or 28 bits in total. The memory is addressed through an address register 20, which is controlled by a time slot counter 22, which also provides some minimal control function. Also coupled to the address register 20 is a last submultiplex address register 24, also controlled by the time slot counter 22.The CPU loads the memory in the same manner as the prior art CBX, though with certain additional characteristics and constraints. In particular, in the prior art CBX, the memory had control over the contents of 376 time slots (as well as the eight reserved time slots). In this embodiment however, the memory has control over the contents of 372 voice channel time slots, the reserved time slots and 40 data channel time slot positions for a total of 420.Thus, in this example, the memory far exceeds that which is required, though has the advantage of being readily reconfigurable to increase the number of data channels at any time as desired. (Reconfiguration can be done automatically by the controller using only knowledge of the number of multiplexed time slots and the total amount of the memory available.) Of the 420 time slots in this example, the CPU loads and regularly updates the memory based on any change of status by organizing the data with the 372 voice time slots first, followed by the time slot information for the first pass through the data time slots, followed by the information for the second pass through the data time slots, etc., with the information for the reserved time slots being stored following the data for the tenth pass through the data time slots.In operation, the address register is incremented through the address of time slots 1 through 372, corresponding to the voice time slots. It is then loaded with the last submultiplex address (one of the addresses for data appearing in one of the ten positions for time slot 376 of Figure 4), then, sequentially incremented in this example four times to step through the particular pass in progress. At this point, the contents of the address register are loaded into the last submultiplex address register 24.The address register is then directed to the address of the first reserved time slot, incremented through those addresses and then returned to the address for the information of time slot one. (Obviously, the system must include a provision to return from the last address of the data time slot information to the first address of the data time slot information and to periodically resync the sequence, though techniques for doing so are well known.) The foregoing embodiment is preferred because it utilizes a relatively conventional memory organization limiting any custom tailoring for a specific application to the program for the CPU and the relatively simple address controller (time slot counter). As such, a system may be readily reconfigured with minimum hardware change.

Now referring to Figure 6, a block diagram illustrating the various interfaces used for data may be seen. A data unit such as terminal 28 is coupled through its output line 30 to a data terminal interface 32, which reformats the data in the preferred embodiment to a standard system format comprising simply a control field and data bits. Typically, a data device such as terminal 28 may have an output conforming to the standard RS 232 format, so that the data terminal interface 32 is simply a data translator. Accordingly, there is no specific system requirement that the data device have an RS 232 output, as the data terminal interface generally could be designed to handle other output formats as well.In that regard, the data terminal interface 32 also serves as a line driver, providing bidirectional translation so as to be capable of sending reformatted data on the telephone line 34 as well as receiving and reformatting to RS 232 (or some other required format) for presentation to the data device 28 on line 30.

The data line interface 36 in this embodiment comprises a card which in general will plug in to the same card slots as the CODECS used for voice communication. The fundamental function of the data line interface is to provide a further bilateral type of data translation or reformatting, specifically by receiving the serial information on line 34 and converting that information to a bit parallel format for coupling to the data bus of the CBX, and for receiving data from the data bus of the CBX in parallel form and putting it out over the phone line 34 in the reformatted serial form.

Obviously serial to parallel and parallel to serial converters are also well known and accordingly, detailed circuits thereof will not be presented.

The data line interfaces 36 may take a variety of forms, though there are two forms specifically worth describing. Generaily, as a minimum, the data line interface 36 will need two addresses, specifically for sensing its call as a source on the source address bus ABO and its call as a destination on the destination address bus AB1.

In particular, since the data bus is operating on a time division multiplexed basis, the data line interface will be addressed in the manner previously described as a source every time it is to present data to the CBX data bus, and must be addressed as a destination every time it is to receive data from the CBX data bus. In accordance with the exemplary description with respect to Figure 4, and assuming the 9,600 BAUD rate still applies, the data line interface would be addressed once as a source for terminal 28 and once as a destination for terminal 28 every ten passes through the connection table or 1 ,200 times per second.

If the data devices (terminals, computers, etc.) were to have fixed connections, the data line interface does not need to have an off hook and ring capability, but instead the CPU could be programmed with the connection information so that the corresponding part of the data time slot connection table never changed. Such a configuration has the advantage of minimizing the cost of the data line interfaces 36, though has the disadvantage that the CPU must be programmed with the connection information for the data devices in some nonvolatile manner. The fixed connection of the data devices is also frequently a disadvantage, as in many cases it is highly desirable for a data device such as a terminal to be able to dial up and communicate with various other data devices on a selective basis, such as various computers in a distributed network.Thus, while the data line interface may simply have a bilateral function of converting serial to parallel and parallel to serial, and responding to two addresses for putting data onto or taking data off of the data bus, it is preferable for maximum flexibility to also include functions similar to off hook and ring, further separately addressable as in the prior art voice system, so that the data devices are not permanently connected, but have a full originate and answer capability. Other functions for connection control, such as data rate in BAUDs are provided as well.

A few things are worth noting at this point regarding the data communications links. In particular, it should be noted that the digital information on the phone line 34 (see Figure 6) is base band digital information, and is not a modulated signal in any form, such as a frequency shift keyed signal. Because of this fact, the resulting data communication over the phone lines is a direct digital communication, as opposed to the communication of a signal modulated in some form by the digital data. Thus, in the present invention the "sampling" rate in bits per second for the phone connection for data communication need not be higher than the maximum data rate in bits per second from or to the particular data device.In contradistinction, frequency shift keying essentially results in an analog signal which would have to be sampled at a rate substantially higher than the data rate to allow the faithful reproduction of the digital information on subsequent demodulation. Also, as has been previously intimated herein, it should be noted that the data bus of the CBX is generally floating, so that the data line interfaces (Figure 6) may be configured to transmit and receive on all 1 6 lines. (Actually, one line is used for a data valid signal to enable the destination data line interface to distinguish valid data from invalid data, as the CBX is regularly transmitting at its own rate, whether or not the data devices are transmitting and/or the rate of that transmission.) Thus on proper configuring of the data terminal interfaces and data line interfaces, the system is not limited to eight bit parallel communication over the CBX data bus. In particular, assuming the data terminal interfaces and data line interfaces are configured to have the full 1 6 bit capability, the 1 6 bits might represent 8 bits of data, a parity bit, a data valid bit and six unused bits. It might also represent eight bits of data, a data valid bit and additional bits for error detection and correction (a Hamming code).Finally, in general the data protocol for the communicating devices is set by the data devices themselves and not by the methods and apparatus of the present invention. All the present invention does is meet the minimum requirements for establishing a data link between data devices without a substantial burden on the switching capacity of the phone system.

The embodiment described with respect to Figures 4 through 6 was described with respect to the connection of 9,600 BAUD devices onto the phone lines of the CBX without a substantial decrease in phone connection capacity of the CBX. It should be noted however, that the 9,600 BAUD rate of this embodiment will also allow the connection of lower speed digital devices through the phone system without any change therein. By way of specific example, if 4,800 BAUD devices were communicating over the phone line at their maximum rate, then approximately every other data sample in the CBX would carry a data valid signal, with the alternate invaiid transfers being ignored by the destination data line interface.

However, if quite a large number of low speed devices are to be used in the system, it may be desirable to provide a system having two data rate connection capabilities, one for the higher speed devices, such as 9,600 BAUD devices, and one for lower speed devices such as, by way of example,1,200 BAUD or lower. In particular, Figure 8A illustrates the conceptual form of the controller connection table of Figure 4 and the embodiment disclosed with respect to Figures 4 through 6. Figure 8B however, presents a similar form of controller connection table modified however, to accommodate in a most efficient manner the connection of data devices of two differing maximum data rates. As before, the upper portion of the connection table is used for voice connection, with the bottom portion thereof being the eight reserved time slots.A portion of the time slots are set aside for data connection information which is further subdivided into regions for first and second maximum data rates, the second data rate being less than the first data rate and accordingly, having more columns therein in the ratio of data rate one divided by data rate two. By way of specific example, if the first data rate is 9,600 BAUD, the description of the embodiment of Figures 4 through 6 is directly applicable to that portion. If, on the other hand, data rate two is 1 ,200 BAUD or one-eighth of 9,600 BAUD, that portion of the controller connection table reserved for source-destination addresses for data rate two may be eight times as wide as for data rate one, i.e., may contain 80 columns of information rather than merely ten as for data rate one.Obviously, while each column of information for data rate one is scanned once every tenth pass or every 830 microseconds, any 'one column for data rate two would be scanned one-eight as frequently, or approximately every 6.7 milliseconds.

The concepts of the implementation of the first embodiment described with respect to Figure 5 may readily be extended to the implementation of the concepts of Figure 8B. This is illustrated in Figure 9 wherein two "last submultiplex address registers" are used, specifically one for the addresses for the information for data rate one and one for the information for data rate two.

Data in the memory itself would be organized in this example with voice channels first, then first pass data rate one information, second pass data rate one information, etc., through tenth pass data rate one information, then first pass data rate two infdrmation, second pass data rate two information, etc., to eightieth pass data rate two information, followed by the eight reserved time slot data positions. the operations of each subportion of Figure 9 is the same as that described with respect to Figure 5, though obviously, while it will only take ten passes to go once through the source-destination information for data rate one, it will take 80 passes to go through the source-destination address information for data rate two.

In the embodiment of Figure 5, the time slot counter must know when to make the step between voice and reserved time slots, and data time slots. This may be accomplished any of a number of ways. One method is to couple a decoder to the source bus ABO to provide a signal to the time slot counter for the start of the submultiplexing sequence. Such a configuation not only provides a start of submultiplexing marker, but at least partly resyncs the system on each pass by repetitively generating this marker on each pass. Another approach is to take a signal directly from the time slot counter and compare it with a corresponding signal representing the first submultiplexing time slot to provide a load signal to load the address register from the last submultiplex address register.

Now referring to Figure 10, a still further alternate embodiment may be seen. In this embodiment a time slot counter 40 provides incrementing signals on a plurality of lines to control counters determining the memory address for a plurality of memories N, each memory containing source-destination address information loadable from the CPU. During the voice time slot portion, incrementing signals would be provided on line 42 to increment counter 44 and sequentially address the sourcedestination locations in memory 46. The addressed information would be selected by multiplexers 48 and 50 via control signals emanating from the time slot counter for coupling to the address lines ABO and AB 1. Memory 46 also would contain memory spaces for the reserved time slots.After cycling once through the locations in memory 46, incrementing of counter 44 would be temporarily halted and counter 52 would be sequentially incremented through line 54. Memory 56, addressed by counter 52, would contain the source-destination information for the 9,600 BAUD data connections organized first pass data first, then second pass data, etc., through the tenth pass data. Counter 52 would increment through one pass of the corresponding portion of the connection table, after which an additional counter would be advanced to address still another memory organized in much the same manner as memory 56. Such a scheme could be carried down to a 300 BAUD level, operating from counter 60 through memory 62.Obviously, the number of lower speed devices, such as 300 BAUD devices, which may be coupled through a single phone connection is extremely large, as for any particular connection, data need only be scanned on every 320th pass. The embodiment of Figure 10 has the disadvantage that the memory containing the controller connection table is actually physically separated and organized as N separate memories. On the other hand, if one multiplexed the addresses into a single memory rather than multiplexing the data out of a plurality of memories, the memory physical configuration and data organization generally reduces to that described with respect to the system of Figures 3 through 6, and/or that described with respect to Figures 8 (a and b) and 9.

There has been described herein new and unique methods for allowing data communication over phone lines and through PBX type equipment on a relatively wide spread basis without undue burden on the switching capacity of the PBX.

Obviously, while the present invention has been described with respect to specific prior art PBX type equipment, i.e., a CBX using a parallel bus structure, the concepts may be readily adapted to other equipment such as, by way of example, PBX type equipment constructed around serial bus structures, whereby data communication may be achieved at rates which are closer to the maximum rates required by the data devices, rather than at the higher rates required for faithful voice reproduction, thereby relieving the switching system of an undue burden on its connection capacity because of the wide spread use of data communication links established through the PBX. Thus, while the present invention has been disclosed and described with respect to certain embodiments thereof, it will be understood by those skilled in the art that various changes in form and detail may be made therein and the inventive concepts thereof applied to equipment of other designs and configurations without departing from the spirit and scope of the invention.

Claims (14)

Claims

1. In a multiline telephone switching system for establishing phone line communication links between any of a first plurality of phone lines wherein phone line connections are momentarily made at a first rate and are time division multiplexed whereby a first predetermined number of phone line connections may be made at said first rate, the improvement comprising:: means for presenting digital data on a second plurality of phone lines comprising a subset of said first plurality of phone lines and at a rate which does not exceed a second rate, said second rate being less than said first rate; means for causing a second number of phone line connections comprising a subset of first predetermined number of phone line connections to momentarily make commanded phone line connections for said second plurality of phone lines at said second rate; whereby the number of commanded phone line communication links for said second plurality of phone lines may exceed said second number of phone line connections.

2. The improvement of Claim 1 wherein the ratio of said first rate and said second rate is an integer.

3. The improvement of Claim 1 wherein said second number of phone line connections is a predetermined number of phone line connections.

4. The improvement of Claim 1 wherein said first rate is sufficiently high to transmit a voice signal across a commanded phone line connection in said switching system.

5. The improvement of Claim 4 further comprised of means for converting analog signals to digital signals and for converting digital signals to analog signals at said first rate, whereby digital signals are transmitted for the phone line connections made at said first rate.

6. A multiline switching system for establishing commanded line connections between any of the lines in a time division multiplexed mode comprising means for establishing a first predetermined number of line connections, each at a first rate and means for causing a second number of line connections selected from said first predetermined number of line connections to be repetitively selected from a third number of line connections, said third number of line connections exceeding said second number of line connections, said third number of line connections being made at a second rate which is less than said first rate whereby some line connections are time division multiplexed at said first rate and some lines are time division multiplexed at said second rate.

7. The system of Claim 6 wherein said second number of line connections is a predetermined number of line connections.

8. The system of Claim 6 wherein said first rate is a rate which will transmit voice signals and said second rate as a rate which will transmit digital data having a predetermined maximum rate.

9. A method of establishing voice and data communication links over phone lines and through a time division multiplexed multiline switching system comprising the steps of (a) establishing line connections for the lines used for voice line connections at a first rate sufficient to reproduce the signal on connected lines, and (b) establishing line connections for the lines used for data communication at a second rate which is lower than said first rate and sufficient to reproduce the data on connected lines at the maximum expected data rate, whereby the number of data communication links which may be made exceeds the number of voice communication links which could have been made with the same line connections.

10. The method of Claim 9 wherein the ratio of said first and second rates is an integer.

11. The method of Claim 9 wherein voice signals are sampled at said first rate and digitized priorto being coupled to said switching system and are converted to analog after passing through said switching system.

1 2. A method of establishing voice and data communication links over phone lines and through a time division multiplexed switching system which may establish up to a predetermined number of line connections per unit of time comprising the steps of (a) establishing a number of line connections at a first rate per unit of time sufficient to reproduce voice information on those lines (b) establishing a number of line connections at a second rate per unit of time sufficient to produce data information on those lines, the second rate per unit of time being less than the first rate per unit of time, whereby the number of data communication links which can be established exceeds the number of voice communication links that can be established for a given number of line connections per unit of time.

13. A method of maximizing voice and data transmissions in a multiline system substantially as herein described.

14. A multiline telephone switching system substantially as herein described and illustrated with reference to Figures 4 to 10 of the accompanying drawings.