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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and to a circuit arrangement for
the transmission of data signals between subscriber stations of a data
network to which subscriber stations operating at different data rates are
connected for the transmission and reception of data signals.
2. Description of the Prior Art
It is well known in the art, in the context of a planned, integrated
services digital network (ISDN) to offer the subscriber stations of an
exchange system different transmission capabilities in that a plurality of
64 kbit/s transmission channels are made available to the subscriber
stations, as reported in the periodical Telcom Report, Vol. 3, No. 3,
1980, pp. 222-227, particularly Page 225. It is not known in this context,
however, how connections are to be set up between such subscriber stations
when the same involves different transmission capacities which are
selectable for the respective connection.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a method and circuit
arrangement for setting up connections in a data network between
subscriber stations that are equipped for different data signal rates or,
respectively, are just incorporated in the connections.
Given a method of the type set forth above, the above object is achieved,
according to the present invention, in that an information signal
identifying the nominal data signal rate desired or possible proceeding
from a calling subscriber station is output by the calling subscriber
station in the course of the set up of a connection or thereafter. The
appertaining information signal is compared call-by-call to preset
parameters existing for the respective called subscriber station or,
respectively, to be called regarding the data signal rates with which the
called subscriber station or, respectively, subscriber station to be
called is able to operate. As a result of the comparison of the
information signal with the preset parameters, that data signal rate is
set in the called or to be called subscriber station which, in view of the
data signal rates given by the information signal, is the highest common
signal rate which is possible for both subscriber stations to be connected
to one another or, respectively, already connected to one another. The
same data signal rate that has been set for the called or to be called
subscriber station is set in the calling subscriber station by
transmitting a setting signal thereto.
The present invention provides the advantage of achieving, in a
particularly simple manner, that data signals can also be transmitted
between such subscriber stations connected in the data network whose
nominal data signal rates are different, but not higher than the
transmission capacity of the connecting circuits. It is further
advantageous that the setting of the data signal rate or, respectively,
transmission rate governing the respective connection can automatically
occur between the subscriber stations connected to one another or to be
connected to one another without separate setting events needing to be
executed in exchange-oriented or transmission-oriented devices.
Given an already existing setting of the respective data signal rate that
is just maximally possible in the respective called subscriber station or,
respectively, subscriber station to be called, and the appearance of an
information signal which relates to a data signal rate that is at most
equal to the first-mentioned data signal rate, only one setting signal for
setting the first-mentioned data signal rate for the calling subscriber
station is output. Deriving therewith is the advantage of a particularly
low control expense for the required setting of the data signal rates to
be used for the respective data signal transmission.
It is expedient for the implementation of the method according to the
present invention to utilize a circuit arrangement that is characterized
in that a data circuit terminating equipment DCE with which the respective
terminal is connected to a transmission line is provided for each
subscriber station, in that parameters regarding which nominal maximum
data signal rate the appertaining subscriber station is designed for or,
respectively, is now operational for are preset in the data circuit
terminating equipment DCE of each subscriber station, in that a comparator
within each data circuit terminating equipment DCE enables the parameters
respectively preset to be compared to an information signal supplied from
a calling subscriber station, the information signal identifying the data
rate just requested by or just possible for the calling subscriber station
for a connection, in that a setting device is connected to the comparator,
that a data signal rate which is the highest-possible common data signal
rate of the data signal rates identified by the information signal and by
the preset parameters in the data circuit terminating equipment DCE is set
by the setting device based on the measure of the output signal of the
comparator in the appertaining subscriber station, and in that
corresponding setting signals can be transmitted from the setting device
of the data circuit terminating equipment DCE of the respective called
subscriber or, respectively, subscriber to be called, these being
transmitted to the data circuit terminating equipment DCE of the calling
subscriber station. Deriving herewith is the advantage of a particularly
low circuit-oriented expense in order to set the maximally-possible data
signal rate or, respectively, the data signal rate to be employed in
common for the respective subscriber stations participating in or to
participate in a connection.
Each signaling unit advantageously comprises a clock selection circuit
which allows clock signals according to the various data signal rates to
be output and which can be set by the setting device for emitting clock
signals corresponding to the data signal rate being considered. This
produces the advantage that the correct clock signals can be offered for
the data signal rates coming into consideration.
In its output position, the clock selection switch preferably outputs clock
signals according to a declared or defined data signal rate. This measure
advantageously opens up the possibility of employing the appertaining,
declared or defined data signal rates for the transmission of signaling
information that are to be transmitted in the course of setting up
connections between subscriber stations and with which the information
signals that appertain to the data signal rates respectively desired or,
respectively, possible for the data signal transmission, can be
transmitted.
It is further advantageous when the setting device of each signaling unit
comprises a bit rate matching device which effects a match between the
data signal rate set at the appertaining subscriber station and a higher
data signal rate which governs on a transmission line connected to the
subscriber station. A clock pulse controlled operation with fixed clock
frequency can be achieved by way of this measure in the overall network.
BRIEF DESCRIPTION OF THE DRAWING
Other objects, features and advantages of the invention, its organization,
construction and operation will be best understood from the following
detailed description, taken in conjunction with the accompanying drawing,
on which there is a single figure which is a block diagram illustration of
an embodiment of apparatus of the invention and for carrying out the
method of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A subscriber station having a data terminal equipment DTE is illustrated on
the drawing, and may be a matter of a data terminal equipment connected
via an interface according to CCITT recommendation X.21 and a series of
circuit devices to a transmission line which includes a line Lan for
transmitting signals in the incoming transmission direction and a line Lab
for transmitting signals in the outgoing transmission direction. The
circuit devices interposed between the transmission line and the data
terminal equipment DEE together form a data circuit terminating equipment
DCE which serves for the automatic setting of data signal rates in the
present case, among other things.
Among other things, the data circuit terminating equipment DCE illustrated
on the drawing comprises an executive sequencing device AS which is
connected to the data terminal equipment DTE by way of a plurality of
lines C, T, R and I. The line C is a control line over which some control
signals required by the executive sequencing unit are supplied. The line T
is a transmission line over which signaling information is supplied to the
executive sequencing unit AS from the data terminal equipment DTE in the
call setup phase. The line R is a receiving line over which signaling
information can be supplied to the data terminal equipment DTE from the
executive sequencing unit AS in the call setup phase. The line I is a
control line over which the executive sequencing unit AS is able to output
control signals to the data terminal equipment DTE.
At its output side and input side, the executive sequencing unit AS, which
executes the respectively-required control events, is connected to a
transmission control unit US which controls the execution of transmission
commands and coding of basic data. The transmission control unit US is
connected with its inputs and outputs via a transmission unit UE to the
aforementioned transmission line, i.e. to the two lines Lan and Lab. The
transmission unit UE essentially serves as a converting device between the
transmission control unit US and the transmission line.
By way of a line Dan for forwarding data signals in the incoming direction
and by way of a line Dab for transmitting data signals in the outgoing
direction, the transmission control unit US is connected to a bit rate
matching device BRA which is further connected at its input and output
sides to the transmission line T and to the receiving line R of the data
terminal equipment DTE. The task of the bit rate matching device BRA is to
undertake a match between the data signal rate utilized in the
appertaining subscriber station or, respectively, at the appertaining data
terminal equipment DTE and the data signal rate of the transmission line
Lan, Lab, regarding which it is to be assumed that it is normally fixedly
prescribed and is higher than the data signal rate for which the
appertaining data terminal equipment DTE is designed.
Also included in the data circuit terminating equipment DCE illustrated on
the drawing is a clock selection circuit TAW which may be connected at its
input side to a clock generator TG whose various outputs Tl-Tn emit clock
signals at different clock rates that can bound to, i.e. synchronized with
a transmission clock from the transmission unit UE which serves as a
reference clock. At a further output T0, the clock generator TG emits
clock pulses that correspond to a defined data signal rate, whereby, in
the present case, this may be a matter of, for example, a data signal rate
of 2.4 kbit/s with which signaling information can be transmitted to and
from respective individual subscriber stations or respective data terminal
equipment.
The clock selection circuit TAW, schematically illustrated as a selector
switch, is connected at its output to one input terminal of a transfer
switch TU comprising two input terminals and one output terminal, the
output terminal thereof being connected via a line S to the data terminal
equipment DTE to which the selected clock pulses are supplied over the
line S. The other input terminal of the transfer switch TU is directly
connected to the output T0 of the clock generator TG. An actuation input
of the transfer switch TU is connected by way of a control line X to the
executive sequencing device AS which switches the transfer switch TU from
its normal switch position illustrated on the drawing into its other
switch position when the signaling phase has been concluded with the
setting of the selected data transmission rate and data signals
transmitted by the data terminal equipment DTE are now to be transferred
to the bit rate matching device BRA or, respectively, data signals output
by the latter are to be forwarded to the data terminal equipment DTE. To
this end, the output of the clock selection circuit TAW is connected to a
clock input of the bit rate matching device BRA.
The clock selection circuit TAW considered above is a component of a
setting device belonging to the data circuit terminating equipment DCE
shown on the drawing and also includes a switch SW having an output for
supplying setting signals for the bit rate matching device BRA and for the
clock selection circuit TAW. At its input side, the transfer switch Sw is
connected to the output of a coding switch CS, on the one hand, and to the
output of a register Reg, on the other hand. A comparator K is connected
to the outputs of the coding switch CS and the register Reg for comparing
the signals supplied thereto from the register Reg via a line or line
group CL1 with the signals supplied thereto from the coding switch CS via
a line or line group CL2, which may be binarily-coded value assignments
regarding the data signal rates to be identified thereby. Overall, the
signals output by the coding switching CS offer preset parameters
regarding the data signal rate with which the subscriber station or data
terminal equipment is able to operate. The comparator K compares these
parameters to an information signal stored in the register Reg proceeding
from the transmission control unit US which had been emitted in the course
of setting up a connection or, respectively, after the completion of
setting up a connection, having been emitted to the subscriber station
shown on the drawing from another subscriber station that may be viewed as
the calling subscriber station and which offers particulars in the
information signal regarding its own data signal rate. The comparator
outputs a specific output signal at its outputs, referenced with < or =
when the value of the information signal intermediately stored in the
register Reg is equal to or higher than the value of the parameters
offered by the coding switch CS. In this case, the transfer switch SW is
located in the switch position shown on the drawing given the appearance
of this specific output signal. In this switch position, that clock signal
rate value designated by the coding switch is selected as the common clock
signal rate value when, as assumed, this value has derived from the
comparison of the parameters and of the information signal as being equal
to or lower than that requested by the remote data circuit terminating
equipment DCE. This value is employed by the circuit arrangement under
consideration for a corresponding setting of the clock selection circuit
TAW via the transfer switch SW. In response to its setting, the clock
selection circuit TAW emits a clock signal at its output having a clock
signal rate that is given by the aforementioned comparison result of the
comparison executed by the comparator K. Stated in other words, this means
that a direct assignment occurs between the respectively-selected clock
signal rate and the data signal rate.
The value employed for setting the clock selection circuit TAW is also
output via a line or line group CL3 to the bit rate matching device BRA
which has therefore received all requisite information in order to
transmit data signals with the correct data signal rate to or,
respectively, from the appertaining data terminal equipment DTE and,
moreover, in order to undertake a match between this data signal rate and
the data signal rate of the transmission line Lan, Lab which is normally
higher in comparison thereto.
It should also be noted that with respect to the register Reg that the
register input is connected to the output of the transmission control unit
US mentioned above. By way of this transmission control unit US, the
register Reg is supplied with only that specific information signal which
had been supplied to the appertaining transmission control unit US from
the transmission line in the bit stream of the whole signaling
information.
The structure of the circuit arrangement illustrated on the drawing having
been considered above, the manner of operation of this circuit arrangement
shall now be considered in greater detail.
It is first assumed that a connection is to be established from a calling
subscriber station having the structure shown on the drawing to a
different subscriber station constructed in a corresponding manner. The
former subscriber station is referred to as the calling subscriber station
and the latter subscriber station is referred to as the subscriber station
to be called.
In a signaling phase, the calling subscriber station first outputs a
signaling information which, for example, contains the call number of the
requested subscriber station to be called. Employed to this end is the
clock signal from the output T0 of the clock generator TG, this being
considered to be clock signal having a clock signal rate of, for example,
2.4 kbit/s, in order to therefore accept the corresponding signaling
information from the data terminal equipment DTE and, forwarded via the
executive sequencing unit AS, to introduce the signaling information into,
for example, a reserved time slot of the transmission control unit AS
which operates in the manner of a multiplexer. In the signaling phase,
further, the calling subscriber station outputs an information signal
which identifies the nominal data signal rate desired by or just possible
for the calling subscriber station. This information signal can either be
output by the data terminal equipment DTE or can be automatically derived
from the position of the appertaining coding switch CS which
correspondingly controls the executive sequencing unit AS via the line or
line group CL2 so that the information signal is transmitted to the
subscriber station to be called or, respectively, already called.
The following operations sequence in the subscriber station to be called
or, respectively, already called. The information signal supplied to the
subscriber station to be called or already called is compared in the
subscriber station to the preset parameter existing there or,
respectively, to the preset parameters existing there which relate to the
data signal rate with which the subscriber station is capable of
operating. As a result of this comparison, that data signal rate which is
the lower data signal rate (i.e. the highest possible common data signal
rate) of the data signal rates practically compared with one another is
then selected in the subscriber station called or to be called. Events
thus sequencing in the subscriber station to be called or already called
completely correspond to the events already considered above in the
context of the explanation of the circuit structure.
After the setting of the data signal rate has been accomplished in the
subscriber station called or to be called, a setting of the data signal
rate in the calling subscriber station is then also required under given
conditions. To this end, the subscriber station to be called or already
called, as just considered, answers back a corresponding information
signal or, respectively, a setting signal to the calling subscriber.
Insofar as the data signal rates selected or, respectively, set in the
subscriber station called or to be called is lower than the nominal data
signal rate that had been specified by the calling subscriber as desired
or possible, a setting now occurs in the calling subscriber station to the
data signal rate that has already been set in the subscriber station
called or to be called. The method of setting the data signal rate in the
calling subscriber station is the same as that in the subscriber station
to be called or, respectively, already called, which method has been
already explained above.
After the conclusion of the events set forth above, both the called and
calling subscriber stations are set to one and the same data signal rate.
This data signal rate is a matter of the respective highest effective
common data signal rate possible with which the two subscriber stations
can enter into data transmission with one another during the connection
which has been established.
By way of transmitting separate control signals, for example in the form of
polarity changes, finally, it can be signaled after the conclusion of the
setting of the data signal rates that data signal transmission can begin.
It thereby suffices for such a signal to be output, for example, from the
calling subscriber station to the called subscriber station since a
corresponding information signal or, respectively, setting signal
regarding the data signal rate has been transmitted from the called
subscriber station to the calling subscriber station.
In conclusion, it should also be pointed out that it has been set forth
above, with respect to the transmission of the information signal
appertaining to the data signal rate, proceeding from a calling subscriber
station that the information signal is transmitted to a called subscriber
station. This, therefore, covers the case that the appertaining
information signal is transmitted from a calling subscriber station to a
called subscriber station during the course of a connection set up, as
well as the case that the appertaining information signal is transmitted
after set up of a connection between a first controlling subscriber
station and a second subscriber station being controlled by the first one.
The same events that have been described above sequence in both cases in
the called subscriber station as well as in the calling subscriber
station.
Conventional, or respectively, commercially available devices can be
employed for the circuit arrangement illustrated on the drawing. The data
terminal DTE is a matter of any data terminal which, e.g. meets one of the
CCITT recommendations X.21 or X.21 bis.
The clock generator TG can be a matter of a traditional clock oscillator
circuit having frequency dividers.
A well-known phase locked loop (PLL) circuit can be used to bind the
generator's clock to the network's clock delivered by the transmission
unit UE.
The clock selection circuit TAW, as well as the switches TU and Sw can be
formed by traditional, controllable semiconductor switches.
The comparator K and the register Reg can likewise be constructed by way of
traditional semiconductor circuits, such as integrated circuits.
The coding switch CS can be a conventional setting switch.
The transmission control unit US and the sequence control unit AS can be
formed by the control portion of a commercially-available data circuit
terminating equipment such as obtainable, for example, from the Siemens
Corporation, Iselin, N.J., under the designation DFG9600 UE-1. The control
portion thereby fulfills both the execution of the call set up and the
call clear down, as well as the execution of the data signal transmission.
Although I have described my invention by reference to particular
embodiments thereof, many changes and modifications of the invention may
become apparent to those skilled in the art without departing from the
spirit and scope of the invention. I therefore intend to include within
the patent warranted hereon all such changes and modifications as may
reasonably and properly be included within the scope of my contribution to
the art.
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