Description
BACKGROUND
1. Field of the Invention
The invention relates generally to communication system and more particularly to a method and apparatus for processing telephone call in a gateway with POTS interface.
2, Related Art
Gateway, in general, refers to a device connected to a communication network that converts information in one format/protocol to other. For example, an IP gateway converts information such as analog voice, multimedia signals, into IP (Internet Protocol) format. The converted information is then transmitted over corresponding communication network. The gateway may be connected to one or more such networks and accordingly may covert the information to one or more corresponding protocols. The gateways arc implemented with multiple interface ports to enable connectivity to various I/O (Input/output) devices, other gateways etc.
Often gateways are implemented support/process telephone calls over different communication network. Telephone call processing often referred to the sequence of operations performed from the acceptance of an incoming call through the final disposition of the call. Alternatively, the end-to-end sequence of operations performed by a network from the instant a call attempt is initiated until the instant the call release is completed.
Accordingly, receive/transmit information from an analog telephone lines/network (also referred to as Plain Old Telephone System (POTS)). POTS

provides an interface (often referred to as POTS interface) to perform telephones calls (voice communication, fax etc). POTS interfaces are provided using FXS (Foreign eXchange Subscriber) and/or FXO (Foreign exchange Office) ports.
A device connected to POTS interface establish telephone calls by transmitting/receiving signals over POTS interface as defined in standard such as Bellcore TR-TSY-000181, Bellcore GR-506-CORE (Signaling for analog Interfaces), KTSI ETS 300 659-2 (Subscriber line protocol over the local loop for display (and related) services) and several other standards recommended by ITU-T.
A FXS port represents the analog line end provided to the subscriber for connecting the terminal device (such as telephone, fax, and a local telephone exchange). The FXS port delivers various control signals (such as dial tone, battery current and ring voltage) required for call processing to subscriber. A FXO port represents the port on the terminal device that receives analog line. The FXO port delivers an on-hook/off-hook indication (loop closure) to exchange office. The gateway with POTS interface may be implemented with any one or both FXS and FXO port.
The gateway with POTS interface enable the subscriber connected to the POPS interface to establish telephone calls over the network connected to the gateway. For example, a gateway connected to IP network may establish telephone call using VOIP protocol. Accordingly, in order to establish telephone calls, the gateway processes telephone call signals received from FXS/FXO port and the network.

BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be described with reference to the following
accompanying drawings.
Figure 1 is a block diagram of communication system illustrating the example
environment in which various aspects of present invention may be
implemented.
figure 2 is a block diagram of apportion of gateway illustrating the call
processing in a prior embodiment.
figure 3 A and 313 are flowcharts illustrating the manner in which a telephone
call is processed in an embodiment of the present invention.
Figure 4 is block diagram of a gateway depicting the example embodiment of
the present invention.
Figure 5 is block diagram of an integrated circuit depicting an example
embodiment of the present invention.
In the drawings, like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements. The drawing in which an clement first appears is indicated by the leftmost digit (s) in the corresponding reference number.
DETAILED DESCRIPTION 1. Overview
A gateway provided according to present invention enable exchange o( information over its POTS interface in a desired format. In one embodiment, gateway receives information in text format from a POTS interface and

converts it to speech signal The speech signal is then transmitted on a desired network such as IP/PSTN/ISON. In case of an IP network is desired for establishing communication, the speech signal is converted to VoIP format and transmitted over IP network. On the other hand speech signal is converted to analog format suitable for transmission over PSTN network if the PSTN network is desired.
Another aspect of the present invention enable user to select the desired communication format (such as speech, text etc) for establishing the call over POPS interface and accordingly provided the information in the selected format.
According to another aspect of the present invention, the information received from the network in various formats (for example VoIP format in case a VoIP call is being received) is converted to text format. The information in text format is then provided to called party (called telephone).
Several aspects of the invention are described below with reference to examples for illustration. It should be understood that numerous specific details, relationships, and methods arc set forth to provide a full understanding of the invention. One skilled in the relevant art, however, will readily recognize that the invention can be practiced without one or more of the specific details, or with other methods, etc. In other instances, well-known structures or operations are not shown in detail to avoid obscuring the features of the invention.

2. Example Environment
Figure 1 is a block diagram of communication system illustrating the example environment in which various aspects of present invention ma\ be implemented. 'The block diagram is shown containing public switched telephone network (PSTN) 110, DSL CPE 120, cable CPE 1W). central gateway 130, central IP network 150, IP PBX 160, POTS terminal devices 140A-140F, FXS/FXO ports 145A-145F, data processing devices 170A and 170B, and imaging devices 180A and 180B. Each block is described below in further detail.
PSTN 110 provides voice communication using circuit switched technique as well known in the field of art. Often PSTN network is also used to transmit digital data and digital voice signal. Hence PSTN is also referred to as integrated service digital network (ISDN). In this document PSTN and ISDN are used interchangeably.
A FXS/FXO terminal is provided at each subscriber premises to connect to the PSTN 110. POTS phones 140A and MOB are shown connected to PSTN network through FXS/FXO interfaces 145A and 145B. Similarly DSL CPE 120, cable CPE 190, and central gateway 130 are shown connected to PSTN network respectively on 121, 191, and 113. Paths 121. WL and 1 13 represents POTS interface.
IP network 150 uses IP protocol to route messages based (m the IP address of the destination. IP network establishes connection using packet switched technique as well known in the field of art. IP network 150 ma\ be implemented on one or more existing communication networks. 1 or example,

portion (connected to DSL CPE 120, and central gateway 130) of IP network 150 is implemented on a PSTN network, while other portion (connected to IP PBX 160 and cable CPE 190) is implemented using a cable network as well known in the field of art.
Accordingly each device (DSL CPE 120, and central gateway 130) connected to IP network 150 is implemented with a modem to convert digital packets into corresponding analog signals suitable for transmitting over PSTN network. Similarly, devices IP PBX 160 and broadband CPE 190 are implemented with cable modem.
Central gateway 130, DSL CPE 120, cable CPE 190. and IP PBX 160 represent example gateways connected to the different networks as shown. Each device is described in further detail.
Central gateway 130 is connected to PSTN network 110 and an IP network 150 respectively on POTS interlace 113 and IP interface I 3:v Accordingly, central gateway 130 converts information in PS IN formal into IP format and vice versa.
Central gateway 130 may route the call through IP network 150 by converting the voice signal into IP packets and vice versa based on the request received from the subscriber. For example, a subscriber ma\ dial a pre specified number indicating central gateway 130 to route call through IP network.

IP PBX (internet protocol PBX) 160 is a gateway connected to IP network and operates as telephone exchange establishing telephone calls over IP network using VOIP protocol. VOIP phone \(^ is shown connected to IP PBX on Ethernet interface 161.
POTS phones HOD and 140E are shown connected to IP PBX 160 on FXS/FXO interlaces 145D and 145E respective!}. IP PBX (internet protocol PBX) 160 performs format conversions on the signals originated when the call is routed to/from POTS telephones 1401) and 1401., and establish connections.
Cable CPE 190 is a gateway connected to IP network 150 and PSTN network 110 respectively on cable interface 159 and FXS/FXO interface 191. Data processing device 170A and Imaging de\iee 1 80A are connected to cable CPE 190 through interface 197and 198 respectively. Interfaces 197 and 198 may represent one of the standard interfaces such as Ethernet, WLAN, and Bluetooth etc.
POTS terminal device HOC is shown connected to cable CPE through FXS/FXO interface 145C. Cable CPE; 190 establishes call routed to/from POTS terminal device 140C using PSTN network or IP network based on the request as noted above.
DSL CPE (Digital subscriber line customer premises equipment) 120 operate similar to the operation of cable CPE 190 described above. Interfacel21 represents the voice analog signal and interface 125 represents the IP packets (containing voice and data) suitabK modulated using a modem.

Since DSL CPH 120 is connected to IP network through PSTN line, both 121 and 125 are transmitted over same physical connection (not shown).
Gateway 120, 130, 160 and 190 receives/transmit information on the l;XS/l;XO port for establishing the telephone call. The signals such as hook events/digits, dial tone, and ring tone, and information generated during the telephone call is converted to a suitable format for transmission on the desired
network.
Implementation of gateways 120, 130, 160 and 190 in an embodiment of the present invention is described with reference to a prior gateway merely for illustration. Accordingly a gateway in prior embodiment is described first below.
3. Prior Gateway.
Prior gateway is implemented to receive/transmit speech/FAX (image encoded according to ITU-T standard as well known in the field of art) signal on the FXS/FXO port for establishing the telephone call. The signals such as off hook, dial tone, and ring tone, speech/FAX signal, generated during the telephone call is converted to a suitable format for transmission on the desired network. The manner in which a call is processed in a prior embodiment is described below.
Figure 2 is a block diagram of apportion of gateway illustrating the call processing in a prior embodiment. Block diagram is shown containing Voice processing unit 250, VoIP protocol converter 2120, PSTN swatch side device 220, andSLlC/SFAC260.

S LIC/SI .AC (Subscriber Line Interface Controller/Subscriber Line Access Controller) 260 provide the analog control signals (indicating the call events) and power to the telephones (example POTS terminal device) connected to PXS/FXO interface. SL1C7SLAC 260 detects call events such on hook, off hook, call request etc. and generates signals such as dial tone, ring tone etc. SI AC/ SLAC may be implemented in a known way. Analogue-to-digital and digital-to-analogue conversion of the control signal may be performed for transmitting over digital packets. The conversion may be performed using VoIP converter 210.
PSTN switch side unit 220 enable connection to the desired called line. Unit 220 provides the digital isolation barrier between the exchanges the gateway. It may also operate to reduce signal distortion/high voltages on the line and relay the PSTN events /tones on to the modem.
VoIP protocol converter 210 receives digitized voice signal/control signal and encapsulate information according to VoIP protocol and provided the packets for transmission over IP network. Similarly, VoIP converter 210 may extract digitized voice signal/control signal from VoIP packets received from the IP network. The extracted signal is then provided to Voice processing unit 210. Interface IP packets transmitted/received on path 211. The path 211 may be provided to a suitable modem for transmission on cable/PSTN/other network interface.
Voice processing unit 250 receives signal from SLIC/SLAC 260, VoIP protocol converter 210 and PSTN switch side device 220 respectively on path

215, 225, and 256. Voice processing unit 250 to establish the call based on the received signal with the terminal device (not shown) connected lo interface 265. Once call is established, voice processing unit 250 may receive voice signal on the POTS interface 265.
The received voice signal is processed based on the desired communication network. In case a connection is requested on an IP network (by dialing a special number), the voice signal is converted into digital data and provided to VoIP protocol converter 210. The converter packetizes the digitized voice signal into IP packets and transmits over IP Network.
Alternatively, when a connection is requested on a circuit switched connection (PSTN network), voice processing unit 250 transmits analog voice signal over the PSTN network. Similarly, voice processing unit 250 converts' digital data received through IP packets to corresponding voice signal The conversion to voice signal from digital data may be perlormed in two stages. hirst the digital data is converted to PCM signal, this operation may be performed by voice processing unit 250. The PCM signal mav then converted to analog signal by SLIC/SLAC 260.
Since prior gateways are implemented to accept voice/1AX signal on POTS interface and to operate on the received voice/T'AX signal, information only in voice or Pax formats are exchanged (communication between the two subscribers) during the call.

Manner in which call is processed in an embodiment of the present invention enabling exchange of information in other formal is described below.
4. Call Processing
Figure 3A and 3B are flowcharts illustrating the manner in which a telephone call is processed in an embodiment of the present invention. In particular, Figure 3A illustrate telephone call processing when call is initiated, while Figure 3B illustrates call processing when a call is received (receiving end).
The flowcharts are described with reference to gateway 120 and communication system of Figure 1 merely for illustration. It may be appreciated that the invention is described with reference to the example system merely for illustration. The extension of the approaches to other communication systems will be apparent to one skilled in the relevant art by reading the disclosure provided herein, and such implementations are contemplated to be covered by various aspects of the present invention.
Continuing with reference to Figure 3 A, the How chart begins in step 301 and control passes to step 310.
In Step 310, gateway 120 receives signal indicating initiation of telephone call with desired handling. The desired handling represents the preferred information format for communication on the POTS port to the terminal device. Signal indicating an off hook event may represents one of the

eall initiation signal. Signal for indicating the desired handling may be generated by dialing a pre specified number.
In one embodiment of the present invention information in a text format is preferred by dialing a pre specified number. According!}, a text message representing a dial tone is transmitted on the POTS interlace. In an alternative embodiment, a dial tone may be generated before receiving the signal indicating the preferred information format. Gateway 120 may receive signal indicating the preferred information format at any time during the call.
In addition to above signals, gateway 120 may receive signals according to V.23/DTM171;SKsignaling and also other signals such as destination number, authentication, desired network, etc signaling required to initiate call.
In step 320, gateway 120 establishes eall and sends a message indicating the establishment of eall. The call may be established in accordance with the received eall initiation signals noted above. Gateway 120 may establish connection on a desired network in accordance with the corresponding protocols.
In step 330, gateway 120 receives information in a desired format on POTS interface and converts to Speech signal. In one embodiment gateway 120 receives the information in text format and converts the text information to speech/voice signal for further processing.
In step 340, gateway 120 transmits the speech \oice signal over desired network. Transmission on a desired network is pcrfornicd b\ encoding the

speech/voice signal into the corresponding format. The How chart ends in step 349.
Due to above approach, gateway of the present invention enable transfer (exchange) of information over POTS interface in the desired format.
In one embodiment of the present invention, text information received on POTS port is first converted to the speech/voice signal. 1 he converted speech/voice signal is then encapsulated into VoIP packets using any of the known technique. The VoIP packets are transmitted on the IP network.
Manner in which call is processed at the receiving side is described below with reference to Figure 3B. The flowchart begins in step 351 and control passes to step 360.
In Step 360, gateway 120 receives an indieation from network on the incoming call to called telephone. Standard signals (such as SIP INVITE message for a VoIP call or a ringing pulse from a PSTN network) representing the indication of call may be received. The gatewax max also receive destination telephone number in case more than one PO'IS telephone are connected the gateway. Gateway 120 may indicate the incoming call to the destination telephone on POTS interface by sending an appropriate signal (call indication signal).
In Step 370, gateway 120 receives signal indicating desired handling from called telephone. The called subscriber may indicate the desired handling by dialing a specific number. Alternatively, gate\\a\ 120 may store the

information representing the desired handling for a user (obtained apriory by offline activity) and retrieve the signal from ihe memory. In case the desired format is known, gateway 120 may send call indication signal (noted in step 360) in the desired format.
In Step 380, gateway 120 converts the received voice/speech signal information to a desired format. In one embodiment, the voice signal received from VoIP or PSTN network is converted to text information.
In Step 390, gateway 120 provides the \oiee speech information on the POTS interface in the desired format.
Due to above approach, the POTS calls established to transfer the information in desired format. One embodiment of the present invention enables calls to be made and received in formats that are convenient to the user. For example, a voice call made at one end max be received as text signal at the receiver and vice versa.
An example gateway implemented according present invention is described below.
5. Example Embodiment
Figure 4 is block diagram o( a gatewax depicting the example embodiment of the present invention. The block diagram is shown containing processing unit 450, VoIP protocol converter 410. PSTN switch side device 420, ST1C/SLAC 460 and text to speech/speech to text converter (TTSC) 480..

SLIC/SLAC 460, PSTN switch side de\iee 440 and VoIP protocol converter 410 operate similar to SLIC/SLAC/ 200. PSTN switch side device 240 and VoIP protocol converter 210 described abo\ e with reference to Figure 2. Hence the description is not repeated for brevity.
TTSC 280 (example of an information format converter) receives text information and converts to corresponding speech information and vice versa. The TTSC may be implemented in a known \\a\ in software or using an additional hardware.
Processing unit 450 receives signal from SLIC/SLAC 460, VoIP protocol converter 410 and PSTN switch side device 420 respectively on path 415, 425, and 456. Processing unit 450 receives the desired handling information through SLIC/SLAC 460 indicating the desired information format as text.
Accordingly, processing unit 450 sends (routes using switch arrangement) text information received on POTS interface 456/465 to TTSC 480. Corresponding speech signal is then processed and encapsulated in to VoIP or PSTN format for transmission on the respective network.
Similarly, processing unit 450 sends the speech/voice information received from VoIP converter and PSTN switch device to TTSC 480. The corresponding text information is transmitted on the POTS interface. The text information may be generated or reproduced using any text enabled telephone systems.

In one embodiment of the present invention the text message is transmitted or received using (V.23/DTMF/FSK) signaling scheme. Alternative schemes may be used for transmitting information in different formats.
Manner in which a VoIP call and PSTN call are established in an embodiment of the present invention is described below with reference 10 Figure 4 and Figure 1.
6. VoIP Call Processing
A user (140C/140F) shall pick up the phone to initiate call. SLICVS1.AC 460 detects an off hook event and plays a dial tone to user 140(\ User 140C dials a special prefix code (indicating special handling of audio) and then dials the VoIP number of the peer (140C/140F)
Processing unit 450 in coordination with central exchange (not shown) and VoIP service provider (not shown) establish a VoIP call with the peer (140C/140F). Since this requires special handling (desiring information format as text), Processing unit 450 generate a text message indicating that the call is connected and transmit the message to phone (140(7140F) using (V.23/DTMF/FSK) signaling.
User (140C/140F) generates and sends the text message (typing the text using the text enable phones) on POTS interface 145C or 4(o, Processing unit 450 detects the text signals invokes the Text To Speech converter (TTSC 480) for conversion. TTSC 480 starts taking the text data and converts to signaling on the 1;XS port.
Similarly, a PSTN/ISDN call may be established o\cv PS I N network instead of VoIP call noted above. Implementation is apparent to ODC skilled in the art by reading the disclosure provided herein. According!) such implementation is and is contemplated to be covered under \arious aspect of the present invention. Por example The PCM signal may be coincrtcd to ie\t format and vice versa to enable exchange of text information on a PS I N call.

Features noted above may be implemented as system on chip in an integrated circuit. An example integrated circuit of the present invention is described below in further detail.
7. Example Gateway.
Figure 5 is block diagram of an integrated circuit depicting an example embodiment of the present invention. The integrated circuit is shown containing PSTN support 510, cable network support 520, Fthernet support 530, WEAN support 540, Bluetooth support 550, FAX/Printer support 5(>0, and signal processing unit 570. Hach block is described below in further detail.
Ethernet support 530 encodes the data (received from signal processing unit 570) in accordance with the Ethernet standards (as well known in the art) and transmit over Ethernet interface 53E Similarly data receixed from the interface 531 is decoded and provided to signal processing unit 570.
Similarly, WEAN support 540, Bluetooth Support 550 encodes and decodes the data in accordance with the respective standards. Number of data processing devices may be connected to interface 541 and :o 1. Fax/printer support 560 represents the interface providing the connects its to 1 ax, printer, imaging units.
Cable network support performs modulation demodulation o\' signals received from the cable network. The demodulated signal is provided to signal processing unit 570 for further processing. Signal recei\ ed from signal processing unit is modulated and transmitted on the interlace 521. Modulation

and demodulation is performed in accordance with the cable modem standards such as DOCSIS as well know in the art.
PSTN support 510 is implemented to support both analog voice communication and digital data transmission on an IP network implemented on the PSTN network. A DSL system represents an example IP network on PSTN network. Interface 511 may contain multiple numbers of FXS/FXO ports. Each unit 510, 520, 530, 540, 550 and 500 may perform desired operation jointly with call processing unit 570.
Call processing unit 570 operate to process PS IN VoIP call to enable exchange of information on interface 511 in the desired format (example Text format) as described above.
In addition, call processing unit 570 may process data/signal received from each support units 510-260 and perform desired operation (such as transmitting data on other interface, printing the data, initiating/terminating a voice call etc.) on the received data.
8, Conclusion
While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of the present invention should not be limited by any o\' the ubo\e described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.

Claims
1/ we claim
1. A method of processing a telephone call in a network device said
method comprising;
receiving a call on a POTS interface;
selecting a first format from a plurality of formats for making communication on said POTS interface;
receiving information in said first format from said POTS interface; and
transmitting said information in a first transmission format over a first network.
2 The method of claim 1, wherein said first format represent a text format.
3 The method of claim 2, wherein said first transmission format represents VoIP protocol and said first network represents IP network

4. The method of claim 2 wherein said first transmission format represents a PSTN Standard format and said first network represents a PSTN network.
5. The method of claim 2 further comprising,
converting said information in said text format to a speech format heforc converting to said first transmission format.
6. The method of claim 1 further comprising;
receiving information from said first network in said first transmission format;
converting information in said first transmission format to speech format
converting information in said speech format to text format; and
providing information in said text format on said POTS interface.

7, A gateway processing a telephone call for selectively establishing communication over a first network and a second network, said gateway comprising;
means for interfacing a POTS terminal device:
means for selecting a first format from a plurality of format;
means for receiving information in said first formal from said POTS terminal device;
means for converting said information in said flrsi format to a first transmission format; and
means for transmitting said information in said firsi transmission format over said first network.
8. The gateway of claim 7, wherein said first format is a text format
9. The gateway of claim 8, wherein said first transmission format and said
first network respectively represent VoIP format and IP network,
10. The gateway of claim 9 wherein said means lor converting further
comprise means for converting said information in text format to a speech
format; wherein said speech format is converted to said fust transmission
format.