DIGITAL DATA INTERFACE UNIT

Abstract: An interface apparatus and method which allows communication of digital data messages between a first type of data terminals (30) employing a message protocol (Fig. 1a) with a ''free text-type'' message, and other user devices (65) employing other digital message protocols. The invention is operable to exploit the free text message capability of the first protocol. In accordance with the invention, the incoming user data messages are packed into one or more free text messages of the first message protocol, and conversely ''unpack'' free text messages from the data terminal employing the first protocol are unpacked and formatted into the message protocol format employed by the user device (65). The invention eliminates the necessity for expensive translation devices which translate the data, and allows a plurality of user data terminals to communicate via a link comprising the data terminals employing the first message protocol.

Description: DIGITAL DATA INTERFACE UNIT BACKGROUND OF THE INVENTION The present invention relates to interface units for allowing digital communication between digital data devices employing different message protocols. There are presently data communications devices in use today which require the data to be packed into specific message formats for reliable data transmission and reception. Examples of such devices are terminals which are employed ' for anti-jam secure radio transmission. There are different types of such terminals in use today, each adapted for communication of digital data in a specific message format. By way of example, the U.S. military employs a tactical radio system known as the "Joint Tactical Information Distribution System" (JTIDS) for tactical information exchange in an anti-jam secure link. JTIDS employs a communication technique known as Time Division Multiple Access (TDMA) which permits mes¬ sages to be sent from numerous terminals on a specified network in a time-sequenced basis. JTIDS is a jam resis¬ tant system using spread spectrum techniques and fast frequency hopping to distribute the transmitted data over a wide frequency bandwidth. Thus, JTIDS information is broadcast omnidirectionally at many thousands of bits per second and can be received by any JTIDS terminal within range. Information flows directly from many transmitters to many receivers; each JTIDS terminal can select or reject each message according to its need for the informa¬ tion. The JTIDS may employ one particular data protocol known as Interim JTIDS Message Set "IJMS", or another protocol known as Tactical Digital Link "TADIL J n -, com¬ prising an alphabet of types of data messages. For example, each IJMS message comprises a header word which defines the type of message, and eight data words contain¬ ing the information. A single message might comprise information such as track report, fuel and ordinance reserves, position, and so on. Other types of terminals also exist, with data protocols which do not coincide with those employed by JTIDS. Military examples include Army Tactical Datalink ATDL-1, TADIL A, and TADIL B. These terminals provide secure transmission capabilities, but are not adapted to provide significant jamming resistance. In many instances, it would be advantageous to allow communication between a JTIDS network and another tactical network such as TADIL B, so as to take advantage of an existing JTIDS network to provide a jamming resistance capability. Thus, there exists a need to provide a means to allow communication between two or more types of commu¬ nication terminals employing different message formats. Attempts have been made to meet this need by the provision of a translator terminal, which receives the information signal from one type of communication terminal employing one specific message format, and "translates" the intelli¬ gence from the terminal into a second type of message format compatible for utilization by the second user. The translation process is understood to involve the decoding of the information in one format, and subsequent encoding of the data into the second type of message format. Such translator devices are subject to translation losses or errors and are very expensive. It would therefore be an advance in the art to provide an improved means for interfacing between data communications terminals employing different message protocols so as to allow communication between such terminals, without employing a data translator. SUMMARY OF THE INVENTION In accordance with the invention, an interface unit is provided to facilitate communication between a first digital data terminal employing a link message protocol comprising a free text message type format and a plurality of other digital data terminals (the "users") employing other message protocols. The invention exploits the free text capability of the link message protocol, wherein the data bits of that message have no predetermined signifi- cance, as is the case with fixed format messages. The interface unit is adapted to pack the incoming digital messages from the user devices into "free text" messages in the link message protocol. Thus, such digital messages from the user device may be communicated via a first interface unit to a first data terminal, and relayed over a communication link to a second data terminal employing the link message protocol for the respective user device. The second data terminal is coupled to a second interface unit which is adapted to recognize and unpack free text- type messages into the appropriate user message protocol. The second interface unit may be coupled to a plurality of user devices. The invention further comprises the method for communicating digital data from one or more user device over a data link comprising first and second link ter¬ minals employing a link message protocol. The link protocol includes a first message type wherein the data bits in selected words do not have a predetermined signif¬ icance. In accordance with the method, user digital data is packed into one or more messages of the first message type and and are provided to the first link terminal for transmission to the second link terminal. The messages received at the second link terminal are unpacked from the link protocol and formatted into the user protocol. This user protocol data is then provided to one or more user devices which employ the user protocol. Hence, the inven¬ tion allows user digital data terminals to communicate via a link comprising the link data terminals employing the first message protocol. BRIEF DESCRIPTION OF THE DRAWINGS These and other features and advantages of the present invention will become more apparent from the following detailed description of an exemplary embodiment thereof, as illustrated in the accompanying drawings, in which: FIG. 1(a) illustrates a first message protocol comprising a free text message, and FIG. 1(b) illustrates a second message protocol. FIG. 2 is a block diagram of a digital data commu- nication link employing the invention. FIG. 3 is a block diagram of the presently preferred embodiment of the interface unit. FIGS. 4(a) and 4(b) are firmware flow charts of the operation of an interface unit employing the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention comprises a novel digital data interface apparatus and method. The following description is presented to enable any person skilled in the art to make and use the invention, and is provided in the context of a particular application and its requirements. Various modifications to the preferred embodiment will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodi¬ ments and applications. Thus, the present invention is not intended to be limited to the embodiment shown, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein. The preferred embodiment of the invention is described in the context of interfacing with JTIDS type radio terminals. These terminals operate with a specific digital message protocol, typically either IJMS or TADIL J. Communications between JTIDS terminals are secure and highly resistant to jamming. Other types of digital radio terminals are in use, such as the TADIL A and TADIL C terminals; these terminals are secure but not resistant to jamming. It is ofteri desirable to have the ability to interface terminals such as the TADIL A or TADIL C terminals to a JTIDS terminal so as to take advantage of an existing jam resistant commu- nications network when the message is being relayed. However, the difference between the message protocol employed by the respective terminals prohibits direct communications between them. A characteristic of the IJMS and TADIL J message protocols, in addition to fixed format messages, is the provision of a "free text" message. That is, the terminal is adapted to recognize an incoming user message which is "tagged" as a free text message, and to format that message so that it is transmitted verbatim to the receiv- ing JTIDS terminal for decoding of the free text message. In effect, the data bits of a free text message are considered as blanks, with no predetermined significance as is the case for fixed format messages. The provision of a free text message in a message protocol is very common, and is not limited to the IJMS and TADIL J proto¬ cols. The universal IJMS message protocol is illustrated by way of example in FIG. 1(a), and comprises an alphabet of messages consisting of 9 digital words each 32 bits in length. The IJMS language comprises a number of different message types, each fulfilling a particular tactical requirement. Specifically the first word of each message block is the "header" word, which includes bit locations whose values define the particular message type. For example, bit positions 1 through 3 in the header word can define the type of message to follow such as, for example, track report, position, mission status, free text, etc. The standard face text message can be further defined as non-error-coded information or error coded information, but position U can indicate if the message has been relayed or received directly from the sender. The next bit positions 5 through 19 can be used to identify the message source by its individual code. Bit position 20-22 specify the category of message such as a track report message, free text, etc. Bit positions position 24 through 26 specify the subcategory such as air track or sea track, etc. Bit positions 27 through 30 label the message such as by specifying which one of up to sixteen air tracks are being sent, or in the case of a free text message, that it is in TADIL-A, TADIL-B, etc. Bit position 31 can identify a special processor, and bit position 32 can identify whether the message is a training purpose message. Of course, the above is merely * an exemplary format for the header word and other formats could be used. As indicated above, one of the message types is the "free text" message. In the free text message, the last eight 32-bit-long words are data words which comprise "blank bits," i.e., the bit values are not assigned any particular intelligence function. These blank bits are available to have bits of information comprising the message to-be-transmitted packed into them. The preferred embodiment of the invention exploits the "free text" message capability of the IJMS or TADIL J - protocol in the communication of digital data, and will first be generally described in connection with the commu¬ nication link block diagram of FIG. 2. The invention comprises user devices such as digital communication devices 10 and 65 each of which comprises a digital radio terminal which employs a non-IJMS message protocol. By way of example, the first such device 10 may utilize the TADIL-A protocol illustrated in FIG. 1 (b) , wherein each message comprises two digital words each 26 bits in length. For this example, it may be assumed that users communicate between the two devices 10 and 65 over commu¬ nications links (not shown) which are secure (i.e., the data is encrypted) but not resistant to jamming. However, it is desirable to be able to employ the JTIDS terminal link to allow secure, jam-resistant communication between the two devices 10 and 65. Thus, two terminals 30 and 45 each comprise JTIDS type radio terminals which communicate via an rf link comprising two antennas 35 and 40. As a result of the different message protocols between the user devices 10 and 65 and the JTIDS radio terminals 30 and 45, two interface units 20 and 50 are provided to respectively interface the devices 10 and 65 to the JTIDS terminals 30 and 45. Hard-wire connections 15 and 25 respectively couple the first user device 10 to the interface unit 20 and the interface unit 25 to JTIDS terminal 30. Similarly, hard-wire connections 60 and 50 respectively couple the user device 65 to the interface unit 55, and the interface unit 55 to JTIDS terminal 45. The interface unit 20 is adapted, in accordance with the invention, to "pack" the user's message from the first user device 10 in a TADIL protocol, for example, into a "free text" message provided in the IJMS protocol. The interface unit 55 is adapted to "unpack" the IJMS free text message into the user's TADIL message format for use by the second device 65, i.e., two words, each 26 bits in length. No translation of the data, with the concomittant translation losses, is required. Thus, communication between the user devices 10 and 65 via the JTIDS link is made possible by the interface units 20 and 55. A general block diagram of a typical interface unit 20 is shown in FIG. 3. Respective user devices 90-93 each employing predetermined message protocols A, B, C, D are coupled to interface unit 20 by data lines 101-104. The user devices may comprise a wide variety of communications devices including, for example, TADIL terminals. . The interface unit 20 comprises a plurality of input/output (I/O) devices 112, 114, and 116, which selectively couple the respective user devices 91-93 to a microprocessor 120 or to respective communication links 134, 136, 138. Thus, for example, communication link 138 may comprise a long range over-the-horizon communication link employing HF (high frequency) or VHF (very high frequency) signals. Link 136 may comprise a short range, UHF link. Link 134 may comprise a modem for connection to a land line link, such as a telephone network. An I/O device 110 couples line 101 to the microprocessor 120 via line 101b. The I/O device 122 couples the microprocessor 120 to a JTIDS link device 132 via lines 124b and 124a. The actual configuration of the I/O devices illus¬ trated in block form in FIG. 3 are conventional types and will depend on the particular user device. For example, a user device may be configured to comply with MIL-STD 1553B, NTDS or the RS232 specifications, which define the user device interface, such as the number of wires and the electrical characteristics of the signal (polarity, voltage level and the like) . The I/O devices are controlled via a control bus 118 to determine the status of the data paths through the I/O devices. Thus, the respective I/O devices 112, 114 and 116 may be controlled so as to couple user line 104 to either line 130 for coupling to the VHF link 138 or to line 117 for coupling to the microprocessor 120. This is to provide the capability of allowing each user device to communicate with the JTIDS communications link 132 through the microprocessor 120, or through other data links not involving the JTIDS terminal. It is to be understood that the structure of the interface unit 20 disclosed in FIG. 3 is merely exemplary, and is intended to illustrate the versatility of interface units which may employ the invention. The microprocessor 120 may comprise any of a number of commercially available circuits, such as the Motorola 6800 microprocessor. Computer programs and data adapted to interface each of the respective user devices to the JTIDS terminal is stored in memory devices such as PROMs (programmable read-only-memorys) for access by the micro¬ processor 120. The microprocessor 120 is programmed to carry out the functions illustrated in the firmware flow chart of FIGS. 4a and 4b. Typical compilers that can be used to generate the computer programs include Pascal, Basic, C-Language and Fortran. The flow diagram of FIG. 4a illustrates the sequence of steps for formatting the user data into IJMS or TADIL J free text messages. The incoming data from the user devices 90-93 is stored at step 200 in a buffer memory within the microprocessor 120. Whether data from one or more of user devices 90-93 is coupled to the microproces¬ sor 120 will depend on the status of the signal on control bus 118, as described above with reference to FIG. 3. At step 205 each respective data protocol type is identified. The data may comprise several possible proto¬ cols A, B, C, or D depending upon the status of the signal on control line 118. The data type may be identified by correlation of the data with the status of the control line 118. Alter- natively, the data protocol of the user device(s) may be predetermined, e.g., where all user devices employ the same message protocol. The data type is "tagged" at step 210, 212, 215 and 220. As was explained in more detail with reference to FIG. la, in the preferred embodiment, a unique digital code is employed to identify each of the respective user message protocols. Each incoming user message is therefore associated or tagged with a prede¬ termined digital identifier. The identifier may be employed to access the appro- priate PROM locations necessary to carry out the next step 225, wherein the "tagged" data is formatted into IJMS free text messages. During this step, IJMS or TADIL J format messages are generated, comprising nine 32-bit words as described with reference to FIG. • la. The IJMS message identifier is specified in the header word as a free text message at bit positions 27 through 30. Additional bits in the header word are reserved for the digital identifier of the user message protocol type. Other bit locations in the header word are employed to identify the specific user terminal to which the message is directed and/or from which the message originated. Thus, the microprocessor is programmed to generate an IJMS free text message, with the header word comprising the free text message identifier and the additional information defining the user message protocol and specific user device. The user message is then copied verbatim into the blank 32 bit data words comprising each IJMS message. Thus, for the user message protocol illustrated in FIG. 1(b), two 26-bit words of each user message are copied verbatim into two of the eight 32-bit data words comprising the IJMS or TADIL J message. Of course, whether the user message is densely packed into the available data bit locations of the IJMS message or spread out over all of the available words is a matter of choice. For example, if a plurality of user messages are input to the interface unit 20 from the same user device, the microprocessor 120 may be programmed to fill each of the available data bit locations of the free text message words with the user message data. Thus, the 52 bits of the user message may be formatted into the 32 bits of the first data word, and the remaining 20 bits formatted into the first 20 bit locations of the second data word. An end-of-message identifier may be placed at the end of the message. Alternatively, the microprocessor 120 may be configured to pack one user message per IJMS or TADIL J message, and the end of each message denoted by an "end- of-message" identifier. Such alternatives may be readily implemented by programming and need not be described in further detail. The formatted IJMS or TADIL J data is then stored at step 230 and then outputted through an output buffer at step- 235 to the JTIDS terminal as one or more IJMS mes¬ sages. The microprocessor 120 when used in the receiver portion of the system is also adapted to "unpack" data moving in the opposite direction, i.e., from the JTIDS terminal to the user terminal 65 (FIG. 1) . The process for unpacking the data is illustrated by the flow chart of FIG. 4b. The incoming data from the JTIDS terminal is coupled into an input storage buffer of the interface unit 55 (FIG. 2) at step 250. At step 255 a decision is made to determine whether the message is a "free text" message; this is accomplished by comparing the message identifier bits in the header word with the predetermined free text code stored in the microprocessor memory. If the message is not a free text message, then at step 260 the processor determines whether an IJMS or TADIL J user is coupled to the interface unit and, if so, passes the message to the IJMS or TADIL J user. If there is no IJMS or TADIL J user, then at step 265 the message can be discarded. In the event that the decision at step 255 is posi¬ tive, i.e., that the message is a "free text" message, then at step 270 the free text message is "unpacked." This is achieved by detecting the type of message from the message protocol type information set forth in the message header and subsequently processing the message to convert the message from the IJMS or TADIL J protocol to the appropriate user protocol such as TADIl-A, for example. Thus, for the example discussed above, the first 26 bits in the first data word of the IJMS or TADIL J message are employed for the first word of the user message and the last 6 bits of the first data word and first 20 bits of the second data word used for the second word of the user message. At step 275 the particular user 65 (FIG. 2) to whom the message is. directed is detected, again from the user identification bits in the message header word, and directed to that user. There has been described an apparatus and method for interfacing one digital data terminal employing a message protocol comprising a free text message to another digital terminal employing a different message protocol. The invention allows digital data communication between such terminals without the need for data translation. It is understood that the above-described embodiment is merely illustrative of the many possible specific embodiments which can represent principles of the present invention. Numerous and varied other arrangements can readily be devised in accordance with these principles by those skilled in the art without departing from the spirit and scope of the invention.

Claims: CLAIMS What is Claimed is: 1. An interface unit for facilitating communica¬ tion of digital data between first and second digital data terminals (30, 45) employing a first message protocol (FIG. la) over a communication link (35, 40) comprising link terminals employing a second message protocol (FIG. lb) which includes a free text message type having bit positions available for packing bits of data therein, comprising: means (20) for packing digital messages received in the first message protocol from said first digital data terminal into the free text digital messages in said second message protocol, for communication of messages from the first terminal (30) over said communi¬ cation link (35, 40) to the second terminal; and means (55) for unpacking free .text digital messages transmitted over said communication link (35, 40) from said second terminal (45) in said second message protocol into digital messages in said first message protocol. 2. The invention of Claim 1 wherein said means (20) for packing digital messages includes a data processor means (120) operable to format digital data received from said second data terminal (45) into free text messages of said first message protocol. 3. The invention of Claim 1 wherein said means for unpacking said free text messages includes a data processor means (120) which is operable to unpack free text messages received from the first data terminal (30) and to format the unpacked digital data into the first message protocol. 4. The invention of Claim 1 wherein said second message protocol comprises a plurality of digital message types, including said free text type, each message type comprising a plurality of digital words, and wherein in accordance with said second protocol a predetermined one of said words comprises dedicated bits indicative of the particular message type, and other ' predetermined ones of said digital ' words comprise data words. 5. The invention of Claim 4 wherein said interface unit comprises a digital computer means (120) including: memory means for storing information defining said first and second message protocols; and means coupled to said memory means for formatting data received from said first terminal into free text messages in the second message protocol, and wherein said formatting means is further operable to define said dedicated bits in said predetermined word comprising said message to indicate that the message is a free text message type. 6. An interface unit (20) for interfacing one or more digital user devices (10) employing a first message protocol (FIG. la) to a digital communication device (65) employing a second message protocol (FIG. lb) com- prising a message type wherein certain data bits of the message have no predetermined data significance, comprising: means (20) for receiving first digital messages of said first message protocol from said user device (10); means (30) for providing second digital data messages compatible with the first data message type of said second protocol; and means (45) for providing first digital signals comprising said certain data bits of said first data messages which correspond to the first digital messages received from said user device (10). 7. The invention of Claim 6 wherein said interface unit further comprises: means for receiving third digital data messages in said second message protocol from said digital communication device (65); means (10) for providing fourth digital data messages compatible with the first message protocol; and means (55) for recognizing those third digital data messages compatible with said message type and generating second digital signals comprising said fourth digital data messages which correspond to said certain data bits of said third digital data messages recoqnized as said message type. 8. The invention of Claim 7 wherein messages conforming to said second message protocol comprise a plurality of digital words each comprising a predetermined number of bits, and wherein a predetermined one of said words comprises bit locations dedicated to defining the message type of the message. 9. The invention of Claim 8 wherein said interface means (20) comprises computer means (120) operable to process said third digital messages from said digital communication device and identify those messages of said data type. 10. An interface unit (20) for facilitating communication of digital data between a communications terminal employing a communication message protocol comprising a free text message type (FIG. la), and one or more user terminals (65) employing a predetermined user message protocol (FIG. lb), comprising: first receiving means (20) for receiving user digital messages from said user device (10); means for providing free text messages in said communication message protocol, said means coopera¬ tively coupled to said first receiving means (20) and operable to provide data portions of said free text messages which correspond to digital data bits comprising said user message; and means (132, 134, 136, 138) for providing said free text messages to said communications terminal. 11. The interface unit of Claim 10 further comprising: second receiving means (45) for receiving digital messages in said communication protocol from said communications terminal (30); means (55) for providing digital data messages compatible with the user message protocol, said means cooperatively coupled to said second receiving means (45) and adapted to provide data portions of said digital data messages, which correspond to data portions of said free text messages; and means for coupling the digital data messages generated by said second generating means (55) to said user terminal (65). 12. The interface unit of Claim 11 wherein said means (20) for providing free text messages is further operable to encode digital bits identifying the predetermined user message protocol in predetermined bit locations of the free text messages. 13. The interface unit (20) of Claim 12 wherein said means for generating free text messages comprises computer means (120) having (i) digital memory means storing data indicative of the communication message protocol and the predetermined user message protocol, and (ii) processing means operable to correlate data bits of the generated free text message to data bits of the received user messages. 14. The interface unit (20) of Claim 13 wherein said means for generating messages compatible with said user message protocol further comprises said computer means (120), and said processing means is operable to determine whether said received communication protocol messages are free text messages, and for the free text messages to correlate the data bits of the generated user message with corresponding data bits of the received free text message. 15. A method for communicating digital data from one or more digital user devices (90, 91, 92, 93) over a data link, comprising the steps of: providing a digital data communication link comprising first and second link terminals (30, 45) employing a link message protocol comprising a first message types wherein the message data bits have no predetermined significance; providing user digital data from the user device in a predetermined user message protocol; packing said user digital data into one or more messages of said first message types; providing said messages to said first link terminal and transmitting them over the data link (35, 40) from the first link terminal (30) to the second link terminal (40); unpacking said messages received at the second link terminal (45) into said user digital data in said user message protocol; and providing said user digital data to one or more of said user devices (65); whereby communication is enabled between said user devices ' over the data link (35, 40) without translation of said ' digital data. 16. The method of Claim 15 wherein said step of packing said user digital data into messages of said first message type comprises the step of writing the user digital data bit-by-bit into one or more predetermined data words comprising said message. 17. The method of Claim 16 wherein said step of unpacking said first data messages received at the second link terminal comprises writing the data bits of said predetermined data words into data messages in said user message protocol. 18. A method for communicating digital data between one or more user devices over a digital data link comprising first and second link terminals (30, 45), comprising: providing a digital data communication link comprising first and second link terminals (30, 45) employing a link message protocol comprising a first message wherein the message data bits have no predetermined significance; providing user digital data from one or more user devices (10), wherein said user digital data is encoded in one of a plurality of predetermined user protocols; packing said user data into one or more of said first messages and providing said first messages to the first link terminal; transmitting said first messages over said data link (35, 40) from said first terminal (30) to said second terminal (45); unpacking said user data from said first messages and formatting said user data into the predetermined user protocol; and providing said user data to one or more user devices (65). 19. The method of Claim 18 wherein said step of packing said user data into one or more of said first messages comprises the steps of: (i) determining the particular user protocol of said user data; (ii) formatting the user data into said first messages; and (iii) tagging said first messages with indicia identifying said particular user protocol. 20. The method of Claim 19 wherein said step of unpacking said user data further comprises the steps of (i) determining the particular user protocol of said (ii messages Comprising said particular user protocol.

Inventors: RICE THOMAS B, RICE, THOMAS, B.
Applicants: HUGHES AIRCRAFT CO, HUGHES AIRCRAFT COMPANY
Application year: 1986
Main classification: H04L11
IPC codes: H04L29