Method for recognizing an off-hook condition on a single subscriber line with two terminal devices

• US 6,934,382 B1
• Filed: 09/27/2000
• Issued: 08/23/2005
• Est. Priority Date: 09/28/1999
• Status: Expired due to Fees

• Current Assignee: Nokia Siemens Networks GmbH & Company KG (Nokia Corporation), Rockwell Technologies, LLC
• Original Assignee: Siemens AG
• Inventors: Kunisch, Paul
• Primary Examiner(s): Kuntz, Curtis
• Assistant Examiner(s): Jamal, Alexander
• Application Number:
  US09/670,648
• Time in Patent Office: 1,791 Days
• Field of Search: 379/377, 379 2903- 2904, 379/207.7, 379/30, 379/381, 379/393
• US Class Current: 379/377
• CPC Class Codes: H04M 3/14 Signalling existence of persistent "off-hook" condition
• CPC Class Codes: H04M 3/2272 Subscriber line supervision circuits, e.g. call detection circuits

Abstract

The invention is directed to a method for recognizing, in a system having a first terminal device and a second terminal device connected to a two-wire subscriber line, an off-hook condition of the second terminal device (2; 3) at the two-wire subscriber line (4) in a switching center (5) or the like, in which the off-hook condition of a first terminal device (3; 2) working in a different frequency band than the second terminal device at the same two-wire subscriber line is recognized by acquiring a loop d.c. (i) and comparing it to a threshold. For reducing the consumable power to be made available in the switching center (5), the invention provides that the loop d.c. (i) is compared to a second threshold that is higher than the first threshold by the minimally required current level in the operation of the first terminal device (3; 2). All off-hook conditions can thus be dependably recognized in the fundamentally same way without providing additional devices and therefore having to make additional consumable power available.

Claims

1. A method in a communications system having a first terminal device and a second terminal device, said method recognizing an off-hook condition of said second terminal device at a two-wire subscriber line in a switching center, comprising the steps of:

acquiring a loop d.c. of a two-wire subscriber line with a first terminal device working in a first frequency band and comparing said acquired loop d.c. to a first threshold, thus recognizing an off-hook condition of said first terminal device; and

comparing said loop d.c. to a second threshold that is higher than said first threshold by a minimally required current level in operating said first terminal device.

2. A method according to claim 1, wherein one of said first terminal device and said second terminal device is an analog terminal device and the other terminal device is a digital or data terminal device.

3. A method according to claim 1, wherein said first threshold is approximately 10 mA.

4. A method according to claim 2, wherein a d.c. resistance of said digital or data terminal device is determined such that is corresponds to that of an analog terminal device at least at a beginning of an off-hook condition.

5. A method according to claim 4, wherein said d.c. resistance is 300 Ω

.

6. A method according to claim 4, further comprising the step of:

lowering said d.c. current of said digital or data terminal device after recognition of said off-hook condition at said digital or data terminal device and a beginning of a data transmission, to approximately 5 mA with an active current source.

7. A communications method, comprising:

measuring in a switching center a loop direct current of a two-wire subscriber line electrically connected to a first terminal device and to a second terminal device;

comparing said loop direct current to a first threshold current, wherein said first threshold current is higher than said loop direct current measured when said first terminal device and said second terminal device are both on-hook;

recognizing an off-hook condition of said first terminal device;

comparing said loop direct current to a second threshold current, wherein said second threshold current is higher than said first threshold current by a minimally required operating current level of said first terminal device; and

recognizing an off-hook condition wherein both first terminal device and said second terminal device are off-hook at the same time.