Telephonic communications – Supervisory or control line signaling – Using line or loop condition detection
Reexamination Certificate
2000-09-07
2004-06-29
Harvey, Minsun Oh (Department: 2644)
Telephonic communications
Supervisory or control line signaling
Using line or loop condition detection
C379S164000
Reexamination Certificate
active
06757378
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for recognizing respective connection requests from telecommunication devices that are connected in parallel to an analog subscriber line, and relates to a telecommunication switching center with a subscriber line-interface, which is configured for recognizing connection requests of a number of telecommunication devices that are connected in parallel to an analog subscriber line.
2. Description of the Prior Art
A particular use of the present invention is referred to as “data-over-voice application”. In data-over-voice applications, analog terminal devices (telephones, fax machines, answering machines, etc.) as well as devices referred to as “multi-standard-fast-modems” (MSFM) are connected in parallel to an analog subscriber line. Preferably, the different devices that are connected in parallel to the analog subscriber line are decoupled via filters for reducing their mutual influence upon one another.
Analog subscriber line circuits generally evaluate the loop closure in the terminal device as an event for a connection request, the indication threshold being at approximately 10 mA and the minimal loop current being at approximately 20 mA.
FIG. 3
shows the loop current through an analog telephone, as is known from Jung, Warnecke, “Handbuch fuer die Telekommunikation”, Springer-Verlag, N.Y., 1998, for example. The signaling of the shown analog telephone
1
is transmitted by means of DC and AC data signals within the transmission range of the telephone network between the telephone
1
and the allocated subscriber switching center
3
via the subscriber line
7
. The connection request is thereby signalized in the analog telephone by means of closing the cradle switch
5
and is therefore signalized by means of a DC loop. Then, a direct-current, which is recognized by an indicator in the switching center
3
, such as a relay or a detector circuit, flows via the cradle switch
5
and the voice circuit M of the telephone. The further actions in the switching center
3
are initiated by the loop indicator, which is now active. When the user hangs up after the conversation, the cradle switch
5
opens and the DC loop is interrupted. The initiation of the utilized devices in the network node is caused by the power-down mode (or idle state) of the loop indicator resulting therefrom.
As already mentioned, the indication threshold (threshold value) for acquiring a connection request lies at approximately 10 mA, and the minimal loop current lies at approximately 20 mA in the steady state. Therefore, loop currents above the threshold value are interpreted as a state referred to as the off-hook state, and loop currents below the threshold value are interpreted as the on-hook state with respect to an existing connection. Since no further differentiation occurs in this conventional circuit, only one application is possible for the analog subscriber line, such as transmission by voice, modem or fax. According to the prior art, the analog subscriber line can only through-connect one speech channel within a frequency range of approximately 200 Hz through 3400 Hz.
This proven method has the advantage that an approximately nonvolatile line monitoring can be realized in the power-down mode. A disadvantage of the technology according to the prior art is that it does not allow recognition of a further event for a connection request on the analog subscriber line when a first occupancy has already ensued.
SUMMARY OF THE INVENTION
An object of the prevent invention is to improve over the known technology for acquiring a connection request so that a number of connection requests on an analog subscriber line can be recognized and processed.
In particular, the following technical requirements should be fulfilled.
connecting a further subscriber terminal device, such as an MSFM, to the analog subscriber line in addition to the already connected analog terminal devices,
no significant interventions with respect to the existing house installation (undoing, rewiring of lines),
mostly independent operation of the analog terminal devices (telephones, fax machines, etc.) and, for example, of an MSFM device that is connected parallel,
recognizing the event for the connection setup and initiating the connection with loop direct-current, for purposes of maintaining the advantages of the approximately nonvolatile line monitoring in the power-down mode,
power management, increasing the loop current when the second occupancy is recognized, for purposes of guaranteeing full functionality of the analog terminal devices and, for example, of the MSFM as far as possible given parallel mode, and
protocol-controlled interruption of the data transmission, where [sic], otherwise, an uncontrolled interference or, respectively, interruption of the data transmission occurs (calling state, fee impulses, for example).
The above object is achieved in accordance with the invention in a method for recognizing a connection request of telecommunication devices that are connected in parallel to an analog subscriber line, wherein each telecommunication device has a cradle switch, and wherein a connection request can be initiated when the cradle switch is closed. The method thereby uses the state, in which none of the cradle switches of the telecommunication devices is closed and therefore none of the telecommunication devices has initiated a connection request, as a baseline.
Proceeding from a first connection request of one of the telecommunication devices, a connection request is initially acquired by the direct-current level in the subscriber line exceeding a first fixed threshold value by means of closing the appertaining cradle switch. The connection request of a further telecommunication device at the analog subscriber line is acquired as soon as the direct-current level in the subscriber line exceeds a further predetermined threshold value. The further predetermined threshold value lies above the first predetermined threshold value.
The further threshold value can be particularly set depending on the direct-current level and direct-voltage drop at the subscriber line, which direct-current level and direct-voltage drop appears in the steady state after the connection request of the first telecommunication device has been acquired.
The further threshold value can be essentially set as the average value between the direct-current level, which appears after the connection request of the first telecommunication device has been acquired, and the expected value, which results when the further telecommunication device initiates a connection request by means of closing its cradle switch.
The acquisition of the connection request of the further telecommunication device cannot be freed before the expiry of a predetermined waiting period after the connection request of the first telecommunication device has been acquired, so that it can be guaranteed that the steady state for the direct-current and direct-voltage relations at the analog subscriber line is present.
A stabilized power supply can be utilized for the subscriber line. Subsequent to the acquisition of the connection request of the further telecommunication device, the feeding characteristics can be modified such the feed current doubles, for example.
For increasing the feed current, a function referred to as a boost (intensifier) function with an increased feed voltage can be utilized.
Subsequent to the completion of the occupancy of one of the first and the further telecommunication device, the modification of the feeding characteristics can be canceled.
The number of telecommunication devices, which are switched in parallel, can transmit in different frequency bands, in particular, so that the possibility exists for decoupling via filters for reducing their mutual influence on one another.
In a further embodiment of the invention, a telecommunication switching center is provided with a subscriber line interface, which is configured for recognizing connection requests of a
Harold Jefferey
Harvey Minsun Oh
Neifeld IP Law PC
Siemens AG
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