Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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DIGITAL DATA INTERFACE UNIT
1 BACXGROUND 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
~Jolnt 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
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1 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~, 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 e~ployed 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 JT~DS
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.
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1 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-
lS cance, as is the case with fixed format messages. Theinterface 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
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type 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
invention allows user digital data terminals to
communicate via a link comprising the link data
terminals employing the first message protocol.
Other aspects of this invention are as follows:
Digital communication apparatus for Use with a
communications link, said commUnications link having a
message protocol Which includes a free text message
protocol, said digital commUnications apparatus allowing
transfer of data, over said communications link, between
digital communiCations terminals of a predetermined type
having a fixed format message protocol whiCh is
incompatible with the message protocol of said
communications link, which comprises:
first means, adapted to receiVe a fixed format
digital message having a fixed format message protocol
from one of said digital communication8 terminals of
8aid predetermined type, for packing said fixed format
digital message into a free text digital message having
a free text me88age protocol compatible with the free
text me88age protocol of 8aid commUnications link; and
8econd mean8, adapted to receive a free text
digital me88age having a fixed format digital me8sage
contained therein from 8aid communication8 link, for
unpacking 8aid fixed format digital message from said
free text digital message, 8aid 8econd mean8 being
adapted to tran8mit said fixed format me88age to one of
8aid digital communication8 terminal8 of said
predetermined type.
Digital communication apparatu8 for use With
8ecure, ~am-re8i8tant digit l communication equipment
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said digital communication equipment having a message
protocol which includes a free text message protocol,
said digital communication apparatus allowing transfer
of data, over said digital communication equipment,
between digital communications terminals of a
predetermined type having a fixed format message
protocol which is incompatible with the message protocol
of said digital communication equipment, said digital
communication apparatus comprising:
first means, adapted to receive fixed format
digital messages having a fixed format message protocol
compatible with said communications terminals, for
packing said fixed format digital message into free text
digital messages having a free text message protocol
compatible with the free text message protocal of said
jam-resistant digital communication equipment; and
second means, adapted to receive free text digital
messages compatible with said communication terminal and
: having a fixed format digital message contained therein,
for unpacking said fixed format digital message from
said free text digital message to provide said fixed
format digital messages for use with said communication
terminals.
A method of producing digital messages compatible
with a communications link derived from a digital
communications terminal employing a message protocol
incompatible with said communications link, said method
comprising the steps of:
storing said fixed format digital message received
from said digital communications terminal;
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identifying the message protocol type of said
fixed format digital message;
tagging said fixed format digital message with
digital identifiers indicating the fixed format message
protocol type, that this message is to be transmitted as
a free text message, and the terminal type to which said
fixed format message is to be transmitted;
formatting said tagged fixed format digital
message into a predetermined free text message format
compatible with said communications link; and
storing said formatted free text message.
A method of communicating between digital
communications terminals employing a fixed message
format and protocol using a communications link
employing an incompatible message format and protocol,
said method comprising the steps of:
storing a digital message having a predetermined
fixed format derived from said digital communications
terminal;
identifying the message~type of said stored fixed
format digital message;
tagging said fixed format digital message with
digital identifiers indicating the fixed format message
protocol type, that this message is to be transmitted as
a free text message, and the terminal type to which said
fixed format message is to be transmitted;
formatting said tagged fixed format digital message
into a predetermined free text message format compatible
with ~aid communications link;
storing a free text message received from said
communications link;
detecting the receipt of said free text message
from said communications link:
unformatting said free text message to extract
said ~ixed format message and identifiers therefrom;
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reformatting said fixed format message into the
message protocol associated with the communications
terminal identified in the transmitted free text
message; and
transmitting said reformatted fixed format message
to the identified digital communications terminal type.
A method of communicating between digital
communications terminals employing a fixed message
format and protocol using a communications link
lo employing an incompatible message format and protocol,
said method comprising the steps of:
storing a digital message predetermined fixed
format derived from said digital communications
terminal;
identifying the message type of said stored fixed
format digital message;
tagging said fixed format digital message with
digital identifiers indicating the fixed format message
protocol type, that this message is to be transmitted as
a free text message, and the terminal type to which said
fixed format message is to be transmitted:
formatting said tagged fixed format digital message
into a predetermined free text message format compatible
with said communications link:
: 25 storing said formatted free text message;
transmitting said formatted free text message over
said communications link;
storing a free text message received from said
communications link;
detecting the receipt of said free text message
from said communications link;
unformatting said free text message to extract
said fixed format message and identifiers therefrom;
unformatting said free text message to extract
said fixed format message therefrom, which includes
determining the fixed format message type, determining
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the terminal to which the fixed format message is to be
sent, and removing the fixed format message from said
free text message; and
transmitting said reformatted fixed format message
to the identified digital communications terminal type.
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. l(a) illustrates a first message protocol
comprising a free text message, and FIG. l(b)
illustrates a second message protocol.
FIG. 2 is a block diagram of a digital data
communication 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
de~cription 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
reguirements. Various modifications to the preferred
e~bodiment will be readily apparent to those skilled in
the art, and the generic principles defined herein may
be applied to other embodiments and applications. Thus,
the present invention is not intended to be limited to
the embodiment shown, but is
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1 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 diqital radio terminals are in use,
such as the TADIL A and TADIL C terminals; thesé terminals
are secure but not resistant to jamming. It is often
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 i8, the terminal
i5 adapted to recognize an incoming user message which is
~tagged~ as a free text message, and to format that
message so that it is transmit.ed 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 a~ blanks, with no predetermined significance
as i8 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-
col~.
The universal IJMS message protocol is illustrated
by way of example in FIG. l(a), and comprises an alphabet
of message~ consisting of 9 digital words each 32 bits in
length. The IJMS language comprises a number of different
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1 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 ca~e of a free text
me8sage, that it i8 in TADIL-A, TADIL-B, etc. ~it
position 31 can identify a special processor, and bit
po~ition 32 can identify whether the message is a training
purpose mes~age. Of course, the above is merely an
exemplary format for the header word and other formats
could be u~ed.
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 n free text~ message capability of the IJMS or TADIL J
protocol in the communication of digital data, and will
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1 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
5 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. l(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 lO 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
u~er device lO 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 mes~age 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
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1 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 lOlb. The I/O device 122 couple~ 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
u~er device interface, ~uch as the number of wires and the
electrical characteristics of the signal (polarity,
* 30 voltage level and the like).
The I/O device~ are controlled via a control bus 118
to determine the status of the data path~ through the I/O
devices. Thus, the respective I/O devices 112, 114 and
116 may be controlled 80 as to couple user line 104 to
either line 130 for coupling to the VHF link 138 or to
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130s23~
1line 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.
10The 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 se~uence
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
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1 predetermined, e.g., where all user devices employ thesame 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
de6cribed 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 mes6age protocol type. Other bit locations in
the header word are employed to identify the specific user
terminal to which the message i8 directed and/or from
which the mes~age originated. Thus, the microproce6sor is
programmed to generate an IJMS free text mes6age, with the
header word compri6ing the free text message identifier
and the additional information defining the user message
protocol and speclfic 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. l(b), two 26-bit words of
each user mes~age 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.
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1 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
lS 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, passeg the message to the
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1 IJMS or TADIL J user. If there is no IJMS or TADIL J
u~er, 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,
~ 5 then at step 270 the free text message is ~unpacked.~
This is achieved by detecting the type of message from the
messaqe protocol type information set forth in the message
header and ~ubsequently 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 aata word and first ~0 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 mes~age header word, and
; 20 directed to that user.
There has been de~cribed an apparatus and method for
lnterfacing one digital data terminal employing a message
protocol comprising a free text message to another digital
terminal employing a different message protocol. The
invention allow5 digital data communication between such
terminals without the need for data translation.
It is understood that the above-described embodiment
i8 merely illu~trative of the many possible specific
embodiments which can repre~ent 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.
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