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1. WO2000033544 - TELEPHONE LINE SHARING MODULE

Note: Text based on automatic Optical Character Recognition processes. Please use the PDF version for legal matters

[ EN ]

Title
TELEPHONE LINE SHARING MODULE

Technical Field
This invention concerns a telephone line sharing module. In another aspect it concerns a system for telephone line sharing. In a further aspect it concerns a method of sharing a telephone line. It also concerns a telephone interface module.

Background Art
Currently, when a single telephone line is being used by a computer (such as a PC) for an Internet session, the line is not available to make or receive telephone calls. Many people overcome this problem by installing a second telephone line dedicated for the computer. Alternatively, it is possible to make and receive calls using a microphone and speakers attached to the computer and its internal sound card.

Summary of the Invention
The invention is a telephone line sharing module, including:
A telephone port, a telephone line emulator associated with the port to emulate the presence of a telephone line, a call conditioner, a telephone line port, a computer interface, and a line switch to selectively switch the telephone port between the telephone line port and the telephone line emulator. In use, the module is arranged to operate such that when a computer connected to the computer interface is using a telephone line of a network, connected to the telephone line port, and a telephone connected to the telephone port is diverted so that incoming calls are received at a gateway site which links the Internet to the telephone network, then the line switch connects the telephone port to the telephone line emulator.
Otherwise, when the computer is not using the line, the line switch connects the telephone port to the telephone line port, and the telephone operates in the conventional way.
When the telephone port is connected to the telephone line emulator, the emulator imitates a telephone line and recognises operations of the telephone, and the call conditioner packages voice data and any dialled numbers from the telephone in a digital form for transmission over the telephone line, and unpackages digital voice data received from the telephone line for transmission to the telephone.
The telephone line emulator may imitate the telephone line to provide tone and ring to the telephone, and also to detect and recognise off-hook and dialling operations of the telephone; in this way it provides a "virtual" telephone connection to the gateway.
The call conditioner may also compress the packages for transmission over the telephone line, and decompress packages received from the telephone line. In addition, the call conditioner may interleave packages with computer data for transmission over the telephone line.
The telephone line need not be a subscription line, but could be a line of a private network, for instance a local network for an office.
When the computer is connected to the Internet via a modem, and the module is also connected to the modem and the necessary IP connection has been established, the module may be automatically activated.
To make an out-going telephone call, while the computer is connected to the Internet, the user picks up the phone and dials the number in the conventional manner. The telephone line emulator imitates the telephone line during this time. The call conditioner decodes the dialled number, packages it as an IP call and it is then sent to the gateway. On receiving the message the gateway dials a normal telephone line and establishes a telephone connection. Once the connection is established the user, computer and gateway exchange voice data in digitised, and if required compressed, format.
When an in-coming telephone call is directed to the gateway it sends a message to the user computer to indicate an in-coming call is received. The telephone line interface then makes the telephone ring. Once the connection is established the user, computer and the gateway exchange voice data in digitised, and if required compressed, format.
The line emulator and call conditioner may comprise a processor to provide
• Full duplex speech compression and decompression
• Tone generation
• DTMF detection
• Codec interface • Automatic handling of frame slippage and frame synchronisation
• Line Echo Cancellation
The computer interface may comprise a Plug and Play interface.
The line switch may comprise a highly sensitive, low power DPDT relay to switch Tip and Ring lines for the telephone between the telephone line and interface circuit. When Power is switched off the switch connects the telephone to the telephone line.
The module could be manufactured as a board for incorporation into a PC, or as a stand alone device. A stand alone device may connect to the telephone line via the computer, and in this case the device may be activated by lifting the receiver of the phone, which then acts as an Internet phone. The module may, in use, be connected between a modem and a conventional telephone, or alternatively it may be incorporated into the modem
Use of the module enables a conventional telephone and a modem to use a single telephone line at the same time.
Advantages of the module are to use a normal phone to make and receive Internet phone calls; call quality may be better than computer bases virtual phones. It is also possible to call PC-to-PC, PC-to-Phone, Phone to-PC, and Phone-to-Phone
Other advantages include:
• Hardware Based Echo-Cancellation
• Full-Duplex Audio & Speaker phone
• Full Telephone Device Support
• Hardware based Compression Reduces Delay and CPU Load
The module is easy to Install. It may use Plug and Play installation

Windows 95/98. It also works alongside existing sound cards (but a sound card is not required). It may also have protection against surges on telephone lines
In another aspect the invention is a system for telephone line sharing, including a telephone line sharing module, as defined, and a gateway site which links the Internet to the telephone network, which are both coupled to each other over a telephone line.
In a further aspect the invention is a method of sharing a telephone line, of a network, between a computer and a telephone, including the following steps: when the computer is using the telephone line and the telephone is diverted so that incoming calls are received at a gateway site which links the Internet to the network, then:
imitating a telephone line and recognising operations of the telephone. and
packaging voice data and any dialled numbers from the telephone in a digital form for transmission over the telephone line, and
unpackaging digital voice data received from the telephone line for transmission to the telephone:
otherwise, connecting the telephone to the telephone line such that they operate in the conventional way.

Brief Description of the Drawing
An example of the invention will now be described with reference to the accompanying Fig. 1, which is a schematic diagram of a telephone line sharing card.

Best Mode of the Invention
In this example the module is a card 1 designed to provide support for public telephone (POTS) network users making it possible to use the telephone while connected to the Internet by using virtual telephone line interface.
The card 1 has two RJll telephone sockets 2 and 3 as with most modems. The telephone line is plugged into one socket 2, and the telephone itself is plugged into the other 3. In addition there is a Plug and Play interface 4. a Control block 5. a G723.1 Processor 6, a Codec 7. a SLIC 8, a Power Block 9. a Ring generator 10 and a Relay 11. The card itself is an ISA bus PC card, the bus being designated 12.
The Plug and Play interface 4 is based on National chip NM95MS15. It provides all the necessary support for PnP interface. The card uses a 16 byte address range easily mapped by PnP onto any PCI/O address range. The card uses one interrupt line, which could be mapped onto one of the eight following lines: IRQ3. IRQ4. 1RQ5. IRQ7. IRQ10, IRQll IRQ12. IRQ15: and one DMA line, which could be mapped onto one of the three following lines: DMA3, DMA6, DMA7 The control block 5 s based on Xilinx XC9536 CPLD. It provides control signals for the G723.1 processor 6. as well as Enable/Disable function for interrupt and DMA. and Shutdown control for the power supply block 9. The CT8020 chip from the DSP Group is used as G723.1 processor 6 and performs the following functions:
• Full duplex speech compression and decompression function
• Tone generation
• DTMF detection
• Codec 7 interface
• Automatic handling of frame slippage and frame synchronisation
• Line Echo Cancellation
• Provides signal for SLIC 8
The processor uses a 3.6864 Mhz external oscillator.
The TP3054b chip from Texas Instruments is used as a codec 7. It is an M-law PCM Codec. It is connected directly to the CT8020 chip. The system uses the following clocks: FSYNC = 8.0Khz and SCLK=2.048Mhz.
An AMD ringing Subscriber line Interface Circuit AM79R79 is used as a SLIC 8. The AM79R79 ringing SLIC device provides BORSHT (battery feed, overvoltage protection, ringing, supervision, hybrid, and test) functions as well as loop current detection, battery switching and relay control. It uses a 24V battery input for loop feed and a 70V battery input for the ring.
A PolySwitch resettable fuse is used for protection from the possible problems in the telephone line.
The power supply block 9 provides -24v and -70v for SLIC operations from the + 12v ISA bus power line. The PC bus is protected by a PolySwitch resettable fuse from any possible failure of the power supply block. When the card is inactive, the power block goes into shutdown mode and does not consume any power. The Control Block 5 controls the shutdown/active mode operation.
The 74HC123A Dual retriggerable monostable multivibrator chip 10 is used to generate Ring reference -20HZ.
A highly sensitive, low power DPDT relay 11 is used. It switches Tip and Ring lines for the telephone between the telephone line and SLIC circuit. When Power is switched off the telephone automatically connected to the telephone line.

Physical Connections:

• Phone port: RJ- 11 2 wire
• PSTN port: RJ-11 2 wire
• 3.5 mm jack microphone
• 3.5 mm speaker out

Phone port
• On Hook Voltage -24VDC or-48VDC
• Nominal Impedance 900 Ohms
• Ring Source 72v Square (α 20Hz
• Ring Drive 5 REN. Short Loop
• Worldwide compatible

Analog Audio Ports
• Microphone impedance 600 Ohm
• Speaker output impedance 32 Ohm

Misc. Specifications
Full Duplex Audio
16 digit DTMF decoding
Programmable Tone Generator
• • Software Selectable G.711, G.723.1, G.728, G.729A and Truespeech compressed audio
Support H.323/H.324 audio
Acoustic and Line Echo-Cancellation in hardware
Auto gain control and software controlled gain and volume

When the computer is not connected to the Internet, the telephone operates in the conventional way, and is connected to the (POTS) telephone line.
Before establishing an Internet connection, a user diverts the phone so all incoming calls are diverted to a special gateway site (SIS) on the worldwide web (WWW) which serves as a bridge between the Internet and the telephone network.

When the computer is connected to the Internet via a modem, and the necessary IP connection has been established, the card's circuitry is activated. The card operates to imitate the telephone line with it's ability to provide tone and ring signals, and also to detect and recognise off-hook and dialling operations; in this way it provides a "virtual" telephone connection to a the gateway.
To make an out-going telephone call, while computer is connected to the Internet, the user picks up the phone and dials the number in the conventional manner. The card 1 will imitate the telephone line, decode the dialled number, package it as an IP call and send it to the gateway. On receiving the message the gateway dials a normal telephone line and establishes a telephone connection. Once the connection is established the user computer and gateway exchange voice data in digitised and compressed format.
An in-coming telephone call is directed to the gateway, and the sends a message to the user computer to indicate an in-coming call is received. The card 1 makes the telephone ring. Once the connection is established the user computer and the gateway exchange voice data in digitised and compressed format as an IP call.
A telephone connected to the card 1 can be used simultaneously and independently of other Internet activity. So, another member of the household could use the phone while somebody is using a computer to access the Internet. While the telephone is in use it consumes around 33% of the Internet time with a modem connection of 28.8 kb and half this with a 56kb speed modem.
The card fully supports Plug and Play 1.0a specifications and is
Windows 95 LOGO compatible. It also fully supports G.723.1 standard. The card does not require PC processor power to encode and decode G723.1 data stream. It also does not require a SoundBlaster card but could coexist with a SoundBlaster card.
G.723.1 is the designation given to the TrueSpeech 6 3/5.3 dual rate speech codec by the International Telecommunications Union (ITU) Study Group 15. G.723.1 is intended to standardise the audio portion of
videoconferencing/telephony over public telephone (:POTS) networks and is part of the overall ITU H.324 standard. It is also recommended as the low bit rate speech coder for the ITU H.323 network conferencing standard for communications on the Internet.
TrueSpeech 6 3/5 3 was selected by the ITU as the G.723.1 standard after extensive testing. TrueSpeech 6.3/5.3 was tested under a variety of conditions including situations with background noise, individuals speaking different languages, male and female talkers, multiple people talking simultaneously etc. The coder was also tested to determine its robustness to hardly lost packets, also called frame erasure. The ability to handle lost packets is especially important to enable high quality voice communication in the Internet environment.
The G.723.1 coder has two bit rates associated with it. These are 5.3 and 6.3 kilobits per second(Kbps). The higher bit rate has better quality. The lower bit rate gives good quality and provides system designers with additional flexibility. Both rates are part of the encoder and decoder. It is possible to switch between the two rates "on the fly". An option for variable rate operation using Voice Activity Detection (VAD), which compresses out the silent portions between words, is also possible.
Using a Pentium 100MHz, the G.723.1 32 bit DLL will encode and decode at approximately 50% of real time. The 16 bit DLL will encode/decode at approximately 85% of real time.
The card is available as a single slot y_ size ISA bus card plugging into PC or MAC computer as well as an external module, which have connection to computer/notebook/organiser via USB port or InfraRed port.
The card does not require computer processor power to encode and decode G723.1 data stream. It also does not require a SoundBlaster card but could coexist with a SoundBlaster card.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.