Hi-fidelity line card

Details Hi-fidelity line card Hi-fidelity line card

1999-05-05

2003-05-20

Cangialosi, Salvatore (Department: 2661)

Multiplex communications

Pathfinding or routing

Combined circuit switching and packet switching

C370S355000, C370S356000

Reexamination Certificate

active

06567399

ABSTRACT:

FIELD OF INVENTION
This invention relates in general to telephony communication networks and more particularly, it is directed to providing a system capable of hi-fidelity audio transmission over existing switched circuit and packet networks.
BACKGROUND OF THE INVENTION
The public switched telephone network (PSTN) was designed during the 1970s. It operates by converting a user's voice to digital information by sampling the analog waveform, transmitting the digital information through the network, and converting it back to an analog waveform at the destination location. A subscriber line interface card (SLIC) typically samples the subscriber's signal at the central office (CO) or other similar facility such as a private branch exchange (PBX). The SLIC samples the audio waveform at a rate of 8 kHz, and produces eight-bit octets for each sample using coding schemes known as &mgr;-law or A-law, resulting in a total bit rate of 64 KBPS. These data bits are transmitted through the network, and at the distant end location the remote SLIC reconstructs the analog signal for analog transmission to the remote subscriber. The sampling rate and quantization scheme used by SLIC devices were chosen to provide acceptable quality voice transmission.
The 8 kHz sampling rate used by the PSTN provides reconstruction of signals up to approximately 4 kHz. However, the human ear is capable of discerning signals with energy content up to approximately 20 kHz, and the human voice can generate sounds up to about 10 kHz. The PSTN audio transmission capabilities, while adequate for subscriber-to-subscriber communication and message comprehension, are well below human capacities with respect to dynamic range and frequency content.
In the existing PSTN, each telephone or other communication device (“subscriber unit”) is typically interconnected by a pair of wires (“tip” and “ring” wires or, cooperatively, “subscriber lines,” “subscriber loop” or “phone lines”) through a series of equipment to a switch at a local telephone CO. At the CO, the tip and ring lines are interconnected to a SLIC, which provides required functionality to the subscriber unit. The switches at the central offices are interconnected to provide a network of switches thereby providing communications between, e.g., a local subscriber and a remote subscriber.
The functions served by the SLIC are commonly referred to as BORSCHT functionality, an acronym for Battery supply (or talking battery), Overvoltage protection, Ringing current supply, Supervision of subscriber terminal, Coder and decoder (Codec), Hybrid (2-wire to 4-wire conversion), and Testing. Generally, these functions include talking battery, ring voltage, ring trip, off-hook detection, and call progress signals such as ringback, busy, and dial tone. In many business office environments, the small-scale function of a central office is assumed by a PBX system, which, in turn, may include a number of SLICs to provide interconnected subscriber units with the required functionality.
Analog subscriber units generate and receive analog signals. While most modern telephone networks are digital and route digital signals from point to point, the subscriber units are still predominantly analog. This is possible because, as mentioned above, the analog signal generated by an analog subscriber unit is converted to digital form for transmission through the network, and is converted at the remote location back to analog form for transmission over the subscriber loop for reception by a remote analog subscriber unit. The analog signals generated and received by analog subscriber units generally take the form of voice frequency signals for end-to-end communications between local and remote subscriber units. Such signals generally represent human speech, or may be modulated signals which are treated by the phone network as if they were ordinary speech signals.
Other analog signals generated or received at the analog subscriber units are supervisory signals that are not intended for transmission to a remote terminal. Rather, they are designed to communicate with the network to enable functions such as call initiation, call progress indication, and call termination. These signals include those provided by, or through, a SLIC such as (i) “talk battery voltage” which provides power to the analog subscriber unit, (ii) “ring voltage” which is a relatively high voltage indicative of an incoming call, (iii) call progress tones such as dial tone, busy tone, and ringback tone. These various signals and tones will be described below.
The subscriber line interface circuit provides DC power, or “talk battery” power, along the phone lines to enable operation of circuitry in subscriber units connected to those lines. Most analog telephone systems work on DC (direct current) power. Typically, the talking battery voltage on analog phone lines is between 5 (off-hook) and 48 volts (on-hook). Talking battery must provide sufficient voltage to enable analog telephones to perform functions such as amplification and sound pickup as well as other phone circuits such as DTMF keypads and speakerphone operation. The talking battery power supply should always be available to an analog telephone, in the event the phone is placed in an off-hook, or closed-circuit state.
A subscriber line interface circuit provides a ring voltage signal to the analog subscriber unit to cause the analog phone to ring in the event of an incoming telephone call. Analog phone systems recognize a ring voltage signal placed on the phone lines by the SLIC, and in turn generate an audible electronic or mechanical ring sound to alert the subscriber of an incoming call. In order to ensure that an analog phone will recognize the ring voltage signal, the ring voltage is required to be 70 to 90 volts (or 140 to 180 volts peak-to-peak AC) at a frequency of 17 to 20 Hz.
A SLIC also passes call progress tones such as dial tone, busy tone, and ringback tone to the subscriber unit. For the convenience of the subscriber who is initiating the call, these tones are provided by the central office as an indication of call status. When the calling subscriber lifts the handset, or when the subscriber unit otherwise generates an “off hook” condition, the central office generates a dial tone and supplies it to the calling subscriber unit to indicate the availability of phone service. After the calling subscriber has dialed a phone number of the remote (answering) subscriber unit, the SLIC passes a ring back sound directed to the calling subscriber to indicate that the network is taking action to signal the remote subscriber, i.e., that the remote subscriber is being rung. Alternatively, if the network determines that the remote subscriber unit is engaged in another call (or is already off-hook), the network generates a busy tone directed to the calling subscriber unit.
The SLIC also acts to identify the status of, or interpret signals generated by, the analog subscriber unit. For example, the SLIC provides −48 volts on the ring line, and 0 volts on the tip line, to the subscriber unit. The analog subscriber unit provides an open circuit when in the on-hook condition. In a “loop start” circuit, the analog subscriber unit generates an off-hook condition by providing a termination, i.e., by closing, or “looping” the tip and ring to form a complete electrical circuit. This off-hook condition is detected by the SLIC (whereupon a dial tone is provided to the subscriber). Most residential circuits are configured as loop start circuits. Some countries, however, have other requirements. Germany, for example, requires a ground to be applied on an additional lead that acts as a control signal.
The SLIC must also be able to detect the off-hook condition during application of ring voltage. That is, when a call is incoming and the SLIC is providing the high amplitude ring voltage signal to the analog subscriber unit, the SLIC must be able to detect when the analog subscriber unit goes off-hook to answer the call. This is known as “ring trip.” The SLIC must immediately

Affiliated with

Also associated with

Rating

Hi-fidelity line card does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Hi-fidelity line card, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Hi-fidelity line card will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3057453