US20010036241A1 - Host signal processor modem and telephone - Google Patents
Host signal processor modem and telephone Download PDFInfo
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- US20010036241A1 US20010036241A1 US09/891,741 US89174101A US2001036241A1 US 20010036241 A1 US20010036241 A1 US 20010036241A1 US 89174101 A US89174101 A US 89174101A US 2001036241 A1 US2001036241 A1 US 2001036241A1
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04M—TELEPHONIC COMMUNICATION
- H04M11/00—Telephonic communication systems specially adapted for combination with other electrical systems
- H04M11/06—Simultaneous speech and data transmission, e.g. telegraphic transmission over the same conductors
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F3/00—Input arrangements for transferring data to be processed into a form capable of being handled by the computer; Output arrangements for transferring data from processing unit to output unit, e.g. interface arrangements
- G06F3/16—Sound input; Sound output
- G06F3/162—Interface to dedicated audio devices, e.g. audio drivers, interface to CODECs
Abstract
A host signal processor (HSP) modem has a software interface between HSP modem hardware and native audio hardware in a host computer. No hard wire connections between modem hardware and audio hardware are required for synchronization. Instead, a software clock recovery system matches a transfer rate of the HSP modem hardware and a transfer rate of the audio hardware by duplicating or deleting samples. The software interface allows the native audio hardware to make audible the handshaking sequence during modem connections which eliminates the need for a speaker and speaker drivers in the modem hardware. The combination of HSP modem hardware, audio hardware, and software executed by the host computer also allows the HSP modem to perform voice communication such as telephone or speakerphone functions.
Description
- The present specification comprises a microfiche appendix. The total number of microfiche sheets in the microfiche appendix is one. The total number of frames in the microfiche appendix is 48.
- A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever.
- 1. Field of the Invention
- This invention relates to systems including multipurpose modems which implement modem and telephone functions using resources such as processors and audio hardware which are native to host computers.
- 2. Description of Related Art
- Multipurpose modems often incorporate digital data and fax functions with speakerphone and answering machine capabilities. Such modems typically have components which serve multiple purposes, such as a speaker which provides an audible sound for monitoring a handshake sequence between connecting modems and provides sound during telephone communications, but many functions require special hardware within the modem which increases the cost of the modem.
- Host signal processor (HSP) modems have been developed which eliminate signal processors and other hardware in the modems in favor or software executed by the processor in a host computer. Software for such HSP modems performs many of the signal and data conversions required of a modem. Use of the host processor reduces modem hardware costs by reducing hardware in the modem. An efficient and inexpensive way to expand an HSP modem to provide standard telephone communications is desired.
- In accordance with the invention, a communication system uses host signal processor (HSP) modem hardware, native audio hardware in a host computer, and procedures executed by the host computer to operate as a modem and a telephone. The native audio hardware provides audio output and/or input for telephone functions. The HSP modem hardware provides the required interface with telephone lines. Operating system protocols allow software communications between the HSP modem hardware and the audio hardware without any direct hardware connections between the HSP modem hardware and the audio hardware even though the audio hardware and HSP modem hardware operate asynchronously with independent sample clocks. A clock recovery procedure executed by the host computer matches data transfer rates and compensates for differences between the independent sample clocks.
- The native audio hardware not only provides resources for expanding the HSP modem to include speakerphone functions but can also make a modem handshake sequence audible for user monitoring. Accordingly, no speakers or speaker driver circuits for monitoring handshake are required in the HSP modem hardware.
- In one embodiment of the invention, a communication system includes an analog-to-digital converter or a codec which converts an analog signal from an input line such as a telephone line to digital samples accessible to a host computer having native audio hardware. Software executed by the host computer transfers the digital samples from the converter to the native audio hardware to provide audible sounds from signal receive on the input line. Digital samples from the host computer (i.e. from a program executed by the host computer or from the audio hardware) are converted to an analog output signal transmitted on an output line.
- In one embodiment, a first index indicates where in a buffer new samples from the HSP modem hardware are transferred, and a second index indicates which samples in the buffer are transferred to the audio hardware. The first index leads the second index to provide a margin between where samples are written and where samples are read. Comparing the first index to the second index indicates whether a difference between the rates at which samples are written and read has increased or decreased the margin. Rates are equalized by duplicating or deleting samples to increase or decrease the margin. This prevents overflow or underflow of the buffer.
- FIG. 1 is a block diagram of a communication system in accordance with an embodiment of the invention.
- FIG. 2 illustrates functional elements of a speakerphone in accordance with an embodiment of the invention.
- FIG. 3 illustrates an HSP modem implementing handshake monitoring through audio hardware native to a host computer.
- Use of the same reference symbols in different figures indicates similar or identical items.
- In accordance with an embodiment of the invention, a host signal processor (HSP) modem includes a software interface between a hardware portion of the HSP modem and native audio hardware in a host computer. The native audio hardware and appropriate software expand the capabilities of the HSP modem to include voice communication such as telephone or speakerphone functions. The audio hardware is native to the host computer in the sense that the audio hardware provides a general purpose audio output and/or input and is not limited to or specifically for use with the HSP modem. Standard operating system protocols control transfers between the HSP modem and the audio hardware, and no special wire connections between modem hardware and audio hardware are required. A software clock recovery system in the HSP modem software matches transfer rates of the HSP modem hardware and transfer rates of the audio hardware even though the HSP modem hardware and the audio hardware have independent sampling clocks.
- In one embodiment of the invention, the native audio hardware in the host computer makes handshaking sequences audible during modem connections. Accordingly, the cost of the HSP modem hardware is reduced by eliminating a speaker and driver circuits for monitoring handshake sequences.
- FIG. 1 shows an
HSP modem 100 similar to the modem described in U.S. patent application Ser. No. 08/428,935, entitled “Communications Interface and Conflict Avoidance Using a Software Simulation of a UART” and U.S. patent application Ser. No. 08/527,668, entitled “Host Signal Processing Communication System that Compensates for Missed Execution of Signal Maintenance Procedures” which are both incorporated by reference herein in their entirety.HSP modem 100 includes a hardware portion (a communication device 130) having an I/O interface 134 connected to abus 120, for example, a local bus in ahost computer 110.Communications device 130 also includes a receive (Rx)buffer 132 and a transmit (Tx)buffer 136 and a codec 135 (combined analog-to-digital converter and digital-to-analog converter). Codec 135 connects totelephone lines 140, converts an analog signal fromtelephone lines 140 into digital samples which are stored inRx buffer 132, and converts digital samples fromTx buffer 136 into an analog signal which is transmitted ontelephone lines 140. - A
processor 112 ofhost computer 110 executes anHSP modem driver 116 which retrieves samples fromRx buffer 132 and writes samples toTx buffer 136 during periodic interrupts. For data or fax modem operations,driver 116 converts the digital samples fromRx buffer 132 according to a standard modem or fax protocol into digital data which are stored in adata buffer 117 for acommunications application 115.Driver 116 also performs the reverse operation of retrieving digital data fromdata buffer 117, converting the data into digital samples, and transferring the digital samples to buffer 136 wherecodec 135 converts the digital samples into an analog signal complying with the standard modem protocol. Incorporated U.S. application Ser No. 08/527,668 further describes modem functions inHSP modem 100. - For telephone communications,
audio hardware 111 which is native to thehost computer 110 provides digital samples representing voice signals to be transmit overtelephone lines 140 and generates sound from digital samples representing incoming voice signals fromtelephone lines 140.Audio hardware 111 may, for example, include a sound card coupled tobus 120 and a microphone and a speaker coupled to an analog-to-digital converter (ADC) and digital-to-analog converter (DAC) on the sound card.HSP modem driver 116 when operating in a voice mode transfers digital samples without conversion according to the modem protocol because the digital samples represent an analog voice signal to be transmitted. Optionally, driver 116 filters or changes the magnitude of digital samples to change the quality or volume of voice signals. One type of filtering in a speakerphone application removes echoes caused by room acoustics. -
Communications application 115 can turn on or off speakerphone operation of the HSP modem. To begin speakerphone operation,communications application 115 opens a communication port serviced byHSP modem driver 116 and then sends a command to place the HSP modem in speakerphone mode.Driver 116 or speakerphone software loaded bydriver 116 then allocates inmain memory 114,buffers audio hardware 111. Software maintains data flow betweencommunication device 130 andbuffers audio hardware 111 andbuffers - Feeding unconverted samples from
communication device 130 throughplay buffer 119 toaudio hardware 111 allowsaudio hardware 111 to play handshake sequences for monitoring of modem or fax connection. Simultaneous with transfer of unconverted samples,driver 116 converts the incoming samples according to the required modem protocol and generates the appropriate response for the handshake sequence. For handshake monitoring,audio hardware 111 requires audio output capabilities such as a sound card and a speaker but does not require audio input hardware such as a microphone.HSP modem hardware 130 can thus monitor handshake sequences without a speaker or other modem hardware conventionally associated with handshake monitoring in modems. - FIG. 2 illustrates an exemplary embodiment of a
communication system 200 which includes HSP modem hardware (communication device 130) and audio hardware including asound card 210, amicrophone 212, and aspeaker 214 which are native to a host computer. In an exemplary embodiment ofsystem 200, the host computer is an IBM compatible personal computer that executes a software portion ofsystem 200 under an operating system such as Microsoft Windows™ 95 or NT which provides for different priority levels. Of the software insystem 200, anHSP modem driver 250 fordevice 130 executes at a higher priority (ring 0) and acommunications application 115 and asound driver 220 execute at a lower priority level (ring 3).Application 115 is a program for accessing multipurpose modems or speakerphones. Such applications are commercially available and include for example, “Microsoft Phone,” available from Microsoft Corporation.Sound driver 220 creates a software interface forsound card 210. Such sound drivers are well known in the art and are normally provided with the operating system orsound card 210. -
HSP modem driver 250 is a custom driver which implements modem and speakerphone operations.Driver 250 includessoftware units units communications application 115 requests opening of the COM port assigned to the HSP modem.Communication application 115 sends the request to an operating system routine (VCOMM) which loads acustom port driver 258 into ring 0. In one embodiment of the invention,port driver 258 implements a software UART for interface todevice 130 andsoftware units port driver 258 is a dynamic device driver executed in ring 0.Port driver 258 loads a small ring 3software routine 225 into the system virtual machine for later use byHSP modem driver 250. The microfiche appendix contains a listing of a module PTSNOOP which implements an example embodiment ofroutine 225. - Once
port driver 258 is loaded into the host computer, the HSP modem is ready to receive standard modem commands.Communication application 115 sends an AT command (AT#CLS=8) todriver 250 viaVCOMM 240 to initiate speakerphone functions.Port driver 258 passes the AT command to controlsoftware 254 which enablesvoice unit 252 and places the HSP modem in speakerphone mode. When first placed in speakerphone mode,voice unit 252 signals routine 225 to start speakerphone operation.Routine 225 allocates memory in the system virtual machine forrecord buffer 118 and playbuffer 119 and then loadsspeakerphone software 230 into the system virtual machine. The microfiche appendix includes a listing of a module PTRTKR which is an embodiment ofspeakerphone software 230. Module PTRTKR is a dynamic load library for the Windows 95 operating system.Speakerphone software 230 sets up an interface withsound card 210 viasound driver 220, transmits the addresses ofbuffers voice unit 252, and then notifiessound card 210 andvoice unit 252 that the system is ready for data transfer. - Communication between
sound driver 220 andspeakerphone software 230 can be conducted via standard sound card protocols such as MCI (multimedia control interface), “direct sound”, or via sound card protocols specially for speakerphones. Under the MCI protocol,speakerphone software 230 requests that sounddriver 220 write a block of audio samples frommicrophone 212 viacodec 215 torecord buffer 118 at a location indicated by an index Rec_Idx.Speakerphone software 230 also requests thatsound driver 220 read and play a data block fromplay buffer 119 starting and an address indicated by an index Play_Idx.Codec 215 converts the block read into asignal driving speaker 214 and producing sound.Sound driver 220 typically reads or writes about 256 or 512 bytes of sound samples per request fromspeakerphone software 230. Upon completion of a block,sound driver 220 makes a callback tospeakerphone software 230 which triggers a requested for transfer of a next block. -
Driver 250 transfers data fromcommunication device 130 to playbuffer 119 and fromrecord buffer 118 tocommunication device 130. In accordance with one embodiment of the invention,device 130 generates periodic interrupts whichdriver 250 services by transferring digital samples. During each interrupt,driver 250 writes 24 samples tocommunication device 130 and reads 24 samples fromcommunication device 130. However, the number of these samples written to or read frombuffers voice unit 252. Ideally, the rates of data input tobuffers device 130 andsound card 210 typically operate asynchronously, difference in clock frequencies fordevice 130 andsound card 210 if left uncorrected can cause data overflow or underflow ofbuffer 118 and/or 119. A hardware connection betweensound card 210 anddevice 130 could synchronize clocks, but most native sound cards do not provide for such hardware connections. - In accordance with an aspect of the invention, a software clock recovery process adjusts data transfer rates to prevent data overflow or underflow. Initially record index Rec_Idx, which indicates where
sound driver 220 writes samples, leads an index TxIndex, which indicates wheredriver 250 reads samples by a fixed amount. For example, index Rec_Idx can initially lead index TxIndex by two full requests of data blocks fromsound driver 220. This lead change if a data transfer rate intobuffer 118 differs from a data transfer rate out ofbuffer 118.Sound card 210 writes sound samples to recordbuffer 118 at the sampling frequency ofcodec 215, for example, at a nominal rate of 8 kHz; and in response to each callback,speakerphone software 230 shifts index Rec_Idx to the next block inbuffer 118 in a circular fashion. Accordingly, index Rec_Idx advances at a rate depending on the sampling frequency ofcodec 215. During the periodic interrupts fordevice 130,driver 250 reads sound samples fromrecord buffer 118 and updates index TxIndex. To prevent overflows or underflows ofrecord buffer 118,driver 250 compares index TxIndex to index Rec_Idx at each interrupt. If index Rec_Idx leads index TxIndex by less than Y bytes, (for example, less than 1 block transfer by sound driver 220), the rate at which samples are read frombuffer 118 is reduced by duplicating one or more samples frombuffer 118 in a block of 24 samples written tocommunication device 130. For example, 23 samples are read fromrecord buffer 118 and index TxIndex is increased by 23, but the last of the 23 samples read is duplicated to form a block of 24 samples written tocommunication device 130. If Rec_Idx leads TxIndex by more than Z bytes, (for example more than 3 block transfers), one or more samples is skipped over so that TxIndex is increased by more than 24 and effective rate at which samples are read frombuffer 118 is increased. In this fashion, the rate of reading data fromrecord buffer 118 adjusts to avoid overflowing orunderflowing buffer 118. - Similarly,
driver 250 balances the read and write rates forplay buffer 119 by comparing indices RxIndex and Play_Idx during each interrupt and adjusting the amount of data written to playbuffer 119. If index RxIndex leads index Play_Idx by less than Y bytes, one or more samples is duplicated to increase the amount of data written to playbuffer 119 during an interrupt. If index RxIndex leads index Play_Idx by more than Z bytes, one or more samples is deleted to reduce the amount of data written to playbuffer 119 during an interrupt. Accordingly, continuous voice communications ontelephone lines 140 are maintained with out overflowing orunderflowing buffers - In addition to, or instead of using native audio hardware for voice communication, an HSP modem in accordance with another embodiment of the invention uses native audio hardware to provide an audible signal for monitoring modem dialing and handshaking sequences. FIG. 3 illustrates an
HSP modem 300 which uses asound card 310 for modem monitoring.HSP modem 300 includes a hardware portion (device 130) andHSP modem driver 250. As described above,HSP driver 250 includessoftware units port driver 258 and routine 225 are respectively loaded into ring 0 and ring 3 in response tocommunication application 115 requesting thatVCOMM 240 open the COM port corresponding fordevice 130. At that point, the HSP modem is ready to receive standard AT commands fromcommunication application 115. - The HSP modem enables a monitoring mode in response to a dial command (ATD) or a ring signal on
telephone line 140 when the HSP modem has been set to answer incoming calls. Whether the HSP enters an audible modem monitoring mode depends on standard AT commands which configure the modem. For example, a user can disable handshake sequence monitoring, can monitor just the handshake sequence, or can monitor modem signals even after the modem connection. To enter monitoring mode,voice unit 252signals software 225 to allocate memory forplay buffer 119 and loadhandshake monitoring software 330 into ring 3.Handshake monitoring software 330 sets up an interface withsound card 310 via an associatedsound driver 320, transmits the address ofbuffer 119 tovoice unit 252, and thenotifies sound card 210 andvoice unit 252 that the system is ready for data transfer. - For handshake sequence monitoring, digital samples are transferred only in one direction, from
device 130 tosound card 210. Accordingly, only play buffer 119 (and not record buffer 118) is allocated. Further,sound card 310 does not require a microphone or an ADC for sound input. ADAC 315 and driver circuits forspeaker 214 are sufficient to produce an audible handshake sequence. - The handshake sequence consists of an output signal from the HSP modem of
system 300 and an input signal generated from a modem or other remote device connected totelephone lines 140.Modem unit 256 generates the output signal which initiates handshaking or responds as required by the desired modem protocol.Voice unit 252 transfers digital samples of an input analog signal ontelephone lines 140 to playbuffer 119 during interrupts as described above in regard to FIG. 2.Sound card 310 plays these samples to generate a sound indicating the progress of the handshake sequence. The output signal from the HSP modem is audible in the sound played bysound card 310 because the output signal echoes back ontelephone line 140 and is represented in the samples transferred byvoice unit 252 to playbuffer 119. - In monitoring mode,
voice unit 252 implements the clock recovery routines as described in regard to FIG. 2. In particular,voice unit 252 monitors the difference between index RxIndex and index Play_Idx and duplicates samples fromdevice 130 to increase the rate of input to playbuffer 119 if the difference becomes too small. To decrease the rate of data transfer intoplay buffer 119, some samples fromdevice 130 are skipped rather than transferred to playbuffer 119 if the difference between index RxIndex and index Play_Idx becomes too large. Accordingly, input and output rates forbuffer 119 are kept about equal to prevent buffer overflow or underflows. - If the HSP modem is configured to stop monitoring upon a connect,
modem unit 256 signalsvoice unit 252 to exit monitoring mode whenmodem unit 256 senses either a successful “connect” to the remote device or a failed handshake sequence. For a successful connect, modem communication can continue with or without audible monitoring of the signals transferred ontelephone line 140 depending on the configuration of the HSP modem. When exiting monitoring mode,voice unit 225signals software 225 to unloadhandshake monitoring software 330 and release memory allocated to playbuffer 119. - Although the present invention has been described with reference to particular embodiments, the description is only an example of the invention's application and should not be taken as a limitation. In particular, although most of the above disclosure above is directed to modems which connect to standard telephone lines, aspects of the invention can also be applied to applications such as cable modems for connection to proposed cable televisions system. Additionally, although example speakerphone applications are described, embodiments of the invention can also be applied to other voice communication functions such as telephone answering machines. Various other adaptations and combinations of features of the embodiments disclosed are within the scope of the invention as defined by the following claims.
Claims (14)
1. A communication system, comprising:
a host computer which includes native audio hardware for generating audible output from the host computer;
a communication device comprising: an interface coupled to the host computer; and an analog-to-digital converter coupled the interface, the analog-to-digital converter converting an analog signal from an input line to digital samples accessible by the host computer through the interface; and
software executed by the host computer, the software transferring the digital samples from the communication device to the native audio hardware which plays the digital samples.
2. The communication system of , wherein:
claim 1
the audio hardware processes digital samples according to a first sampling clock;
the communication device processes digital samples according to a second sampling clock which is asynchronous to the first sampling clock; and
the software comprises:
a buffer in a memory of the host computer; and
a procedure which transfers digital samples from the communication device to the buffer, wherein the procedure duplicates or deletes samples to equalize a data transfer rate from the communication device and a data transfer rate to the audio hardware.
3. The communication system of , wherein:
claim 2
samples from the communication device are transferred from the communication device to a location in the buffer, indicated by a first index;
samples are transferred to the audio hardware from a location in the buffer, indicated by a second index; and
the procedure compares the first index to the second index and determines from a difference between the first and second indices whether to duplicate or delete samples being transferred to the buffer.
4. The communication system of , wherein:
claim 2
the communication device further comprises a digital-to-analog converter coupled to the interface, the digital-to-analog converter converting digital samples from the interface into an analog signal transmitted on an output line; and
the software further comprises:
a second buffer in the memory of the host computer; and
a second procedure which transfers digital samples from the second buffer to the communication device, wherein the second procedure duplicates or deletes samples to equalize a data transfer rate from the communication device and a data transfer rate to the audio hardware.
5. The communication system of , wherein:
claim 1
the communication device further comprises a digital-to-analog converter coupled to the interface, the digital-to-analog converter converting digital samples from the interface into an analog signal transmitted on an output line; and
the software transfers digital samples from the audio hardware to the communication device for conversion to a transmitted analog signal.
6. The communication system of , wherein the software provides voice communications when operated in a first mode during which digital samples are transferred between the audio hardware and the communication device and provides modem functions when operated in a second mode during which digital samples are converted according to a modem protocol to generate data.
claim 1
7. A host signal processor modem comprising:
a communication device comprising an interface for connection to a host computer, and an analog-to-digital converter which converts analog signals from an input line to digital samples accessible to the host computer through the interface; and
software executed by the host computer, the software including a procedure which during a handshake sequence for the host signal processor modem, transfers digital samples from the communication device to audio hardware native to the host computer, the audio hardware playing the digital samples to allow user monitoring of the handshake sequence.
8. The host signal processor modem of , wherein the software deletes or duplicates digital samples being transferred, as necessary to equalize a transfer rate from the communication device and a transfer rate to the audio hardware.
claim 7
9. The host signal processor modem of , wherein:
claim 7
the audio hardware processes digital samples according to a first sampling clock;
the communication device processes digital samples according to a second sampling clock which is asynchronous to the first sampling clock; and
the software comprises:
a buffer in a memory of the host computer, wherein samples from the communication device are transferred from the communication device to a location in the buffer, indicated by a first index and samples are transferred to the audio hardware from a location in the buffer, indicated by a second index; and
a procedure that compares the first index to the second index and determines from a difference between the first and second indices whether to duplicate or delete digital samples.
10. The host signal processor modem of , wherein the communication device generates an audible modem handshake sequence solely through audio hardware native to the host computer.
claim 7
11. A method for operating a host signal processor modem, comprising:
transferring digital samples from an analog-to-digital converter in a hardware portion of the host signal processor modem to a buffer in a host computer which executes a software portion of the host signal processor modem; and
using audio hardware native to the host to play the digital samples from the buffer.
12. The method of , wherein the digital samples represent and analog signal input to the host signal processor during a handshake sequence.
claim 11
13. The method of , wherein transferring the digital samples comprises duplicating digital samples from the hardware portion of the host signal processor modem to increase a data transfer rate to the buffer and match a rate at which the audio hardware plays the digital samples from the buffer.
claim 11
14. The method of , wherein transferring the digital samples comprises skipping transfer of some digital samples from the hardware portion of the host signal processor modem to decrease a data transfer rate to the buffer and match a rate at which the audio hardware plays the digital samples from the buffer.
claim 11
Priority Applications (1)
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US09/891,741 US20010036241A1 (en) | 1996-07-09 | 2001-06-25 | Host signal processor modem and telephone |
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US08/677,485 US5940459A (en) | 1996-07-09 | 1996-07-09 | Host signal processor modem and telephone |
US09/327,945 US6252920B1 (en) | 1996-07-09 | 1999-06-08 | Host signal processor modem and telephone |
US09/891,741 US20010036241A1 (en) | 1996-07-09 | 2001-06-25 | Host signal processor modem and telephone |
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US09/327,945 Continuation US6252920B1 (en) | 1996-07-09 | 1999-06-08 | Host signal processor modem and telephone |
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US09/327,945 Expired - Lifetime US6252920B1 (en) | 1996-07-09 | 1999-06-08 | Host signal processor modem and telephone |
US09/891,741 Abandoned US20010036241A1 (en) | 1996-07-09 | 2001-06-25 | Host signal processor modem and telephone |
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US09/327,945 Expired - Lifetime US6252920B1 (en) | 1996-07-09 | 1999-06-08 | Host signal processor modem and telephone |
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2001
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US9564985B2 (en) * | 2012-11-27 | 2017-02-07 | Diebold Self-Service Systems Division Of Diebold, Incorporated | Automated banking machine that outputs interference signals to jam reading ability of unauthorized card reader devices |
CN108880696A (en) * | 2017-05-12 | 2018-11-23 | 中兴通讯股份有限公司 | Frequency configuration handshake method and system, terminal and computer readable storage medium |
Also Published As
Publication number | Publication date |
---|---|
US6252920B1 (en) | 2001-06-26 |
US5940459A (en) | 1999-08-17 |
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