Telephonic communications – Telephone line or system combined with diverse electrical... – Having transmission of a digital message signal over a...
Reexamination Certificate
2001-02-02
2003-06-03
Ramakrishnaiah, Melur. (Department: 2643)
Telephonic communications
Telephone line or system combined with diverse electrical...
Having transmission of a digital message signal over a...
C379S093280, C379S090010, C455S465000, C370S468000
Reexamination Certificate
active
06574315
ABSTRACT:
BACKGROUND OF THE INVENTION
Data telecommunication (datel) is the mutual sending and receiving of data or data signals (packet data) between a data terminal equipment item—e.g. personal computer, data terminals, DP systems etc.—and a remote data terminal equipment unit—e.g. personal computer, data terminals, DP systems etc.—via a telecommunication network, for example a public telecommunication network (ISDN, PSTN etc.). So that the data or data signals sent by the data terminal equipment unit can be transmitted via the telecommunication network, a network facility, the so-called data communication equipment unit, is provided between the data terminal equipment unit and the telecommunication network. Apart from the PC card (previously: PCMCIA card), the most widely used data communication equipment item is the modem (made up of modulator/demodulator) [compare also the utility model DE 297 14 588 U1].
The modem is an electrical data communication equipment unit operating on the basis of the carrier-current method for use on analog transmission paths of limited bandwidth—e.g. telecommunication lines (e.g. a/b circuit pair, ISDN-S
O
-BUS etc.) of the telecommunication network which converts digital data signals into analog data signals and conversely and transmits them. Furthermore, a multiplicity of methods of the V series standardized by the International Telecommunication Union - Telecommunication Standards (ITU-T) - are implemented in modems.
FIG. 1
shows a data telecommunication scenario based on a V.24 data transmission system. A V.24 data transmission system is connected to a remote V.24 data transmission system via a public telecommunication network, for example a PSTN (Public Switched Telecommunication Network) exhibiting an a/b circuit pair or an ISDN (Integrated Services Digital Network) exhibiting an ISDN-S
0
-bus. The V.24 data transmission system exhibits a data terminal equipment unit DTE constructed, for example, as personal computer and a data communication equipment unit DCE constructed, for example, as a modem, which are connected to one another via a V.24 cable (V.24 interface) K
V.24
.
Analogously to the above, the remote V.24 data transmission system exhibits a remote data terminal equipment unit DTE
r
constructed, for example, as a personal computer and a remote data communication equipment unit DCE
r
constructed, for example, as a modem which are also connected to one another via a V.24 cable (V.24 interface) K
V.24
.
The data terminal equipment unit DTE, DTE
r
contains a system controller SST with a user interface BOF, application software ASW and a driver TR as an interface adapter between software (application software) and hardware (data communication equipment unit or, respectively, modem).
The driver TR is specific to the modem manufacturer and preferably constructed as CAPI (Common ISDN Application Programmable Interface; standardized communication interface for user software for the error-tolerant ISDN telecommunication with the personal computer) driver or as TAPI (Telephone Application Programmable Interface) driver.
A plurality of the data communication equipment units DCE which can be obtained on the market, e.g. analog modems and ISDN terminal adapters external to the PC are controlled via a HAYES instruction set (or HAYES standard). The HAYES standard was originally an American industry standard for modem communication, especially for modem control by the data terminal equipment unit DTE. It is also called the AT standard because almost all instructions of the HAYES instruction set begin with the prefix “AT” (Attention) comprising the ASCII characters A and T. The standard which, in the meantime, has been introduced throughout the world, is the subject matter of an ITU Recommendation (International Telecommunication Union) designated by “ITU-T V.25ter”. Instead of the prefix “AT”, the prefix “at”, the prefix “A/” or the prefix a/” can also be used.
In these modems, the modem driver TR of the data terminal equipment unit DTE changes the baud rate at the V.24 interface depending on the data transmission phase (e.g. connection set-up, negotiation of the transmission parameters etc.). This change in baud rate is transmitted via the V.24 cable K
V.24
to the data communication equipment unit or modem, respectively, DCE, but not by means of signaling. Thus, the modem DCE must automatically detect the newly set baud rate and adapt itself to the driver TR (autobauding). The relevant rule is: the baud rate at which the “AT” character sequence is transmitted is valid until the next “AT” character sequence is received.
This autobauding is active in the modems until the modem has changed into the user data transmission mode, or the so-called “transparent mode” after a connection set-up. In this mode, a “point-to-point” connection (“end-to-end” connection) exists with the remote data communication equipment unit or, respectively, remote modem DCE
r.
Autobauding is then switched off so that “AT” character sequences are not interpreted in the user data stream and there is possibly an unwanted change in baud rate at the modem.
The V.24 cable or, respectively, V.24 interface K
V.24
supports the modem operation on a personal computer by means of various lines (status lines) in accordance with ITU-T Specification V.24 , March 1993, pages 1 to 19. These lines are:
1. A transmit data line TxD for data transmission,
2. a receive data line RxD for data transmission,
3. an RTS (Ready To Send) line RTS for the “hardware handshake” type of transmission for transmitting the “READY TO SEND” state (“RTS” state),
4. a CTS (Clear To Send) line CTS for the “hardware handshake” type of transmission for transmitting the “CLEAR TO SEND” state (“ICTS” state),
5. an RI (Ring Indication) line RI for detecting ringing at the modem,
6. a DSR (Data Set Ready) line DSR on which the modem reports to the personal computer that it is switched on,
7. a DTR (Data Terminal Ready) line DTR on which the personal computer reports to the modem that it is switched on and is ready to accept calls,
8. a DCD (Data Channel Detection) line DCD on which the modem reports to the personal computer that it has accepted and set up the connection to a remote modem,
9. a ground (GrouND) line GND.
If the V.24 cable or V.24 interface K
V.24
does not have the nine lines listed above but has fewer than nine, e.g. seven, this 7-wire cable can still support the modem operation on the personal computer. This is possible due to the fact that, instead of the “hardware handshake” on the RTS/CTS lines, a “software handshake” type of transmission is performed for transmitting the “RTS”, “CTS” states—e.g. by means of an XON/XOFF protocol - on the transmit/receive data lines TxD, RxD. In the “software handshake”, the data stream transmitted between the data terminal equipment unit DTE and the data communication equipment unit DCE is analyzed in the data terminal equipment unit DTE and the data communication equipment unit DCE, all “software handshake signals” are interpreted and measures are correspondingly initiated.
For an application scenario in which the data terminal equipment unit DTE and the data communication equipment unit DCE are spatially separated from one another, e.g. by several meters, the cord-connected V.24 data transmission system shown in
FIG. 1
exhibits the disadvantage that first, a V.24 cable K
V.24
, the length of which corresponds to the spatial arrangement of data terminal equipment unit DTE and data communication equipment unit DCE, is required for the data telecommunication and, secondly, a large, not inconsiderable effort is expended for running the cable for the installation of the system with such cable lengths.
Analogously to cordless telephony, it is therefore desirable and also imaginable to replace the cord-connected V.24 data transmission system according to
FIG. 1
with a cordless V.24 data transmission system.
On the basis of
FIG. 1
,
FIG. 2
shows such a cordless V.24 data transmission system for data telecommunication. The remote V.24 data transmission system
Alfaro Diego Garcia
Biedermann Rolf
Bell Boyd & Lloyd LLC
Ramakrishnaiah Melur.
Siemens Aktiengesellschaft
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