Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
  • H04W88/16—Gateway arrangements
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N1/00—Scanning, transmission or reproduction of documents or the like, e.g. facsimile transmission; Details thereof
  • H04N1/00127—Connection or combination of a still picture apparatus with another apparatus, e.g. for storage, processing or transmission of still picture signals or of information associated with a still picture
  • H04N1/00281—Connection or combination of a still picture apparatus with another apparatus, e.g. for storage, processing or transmission of still picture signals or of information associated with a still picture with a telecommunication apparatus, e.g. a switched network of teleprinters for the distribution of text-based information, a selective call terminal
  • H04N1/00307—Connection or combination of a still picture apparatus with another apparatus, e.g. for storage, processing or transmission of still picture signals or of information associated with a still picture with a telecommunication apparatus, e.g. a switched network of teleprinters for the distribution of text-based information, a selective call terminal with a mobile telephone apparatus
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
  • H04N2201/00—Indexing scheme relating to scanning, transmission or reproduction of documents or the like, and to details thereof
  • H04N2201/32—Circuits or arrangements for control or supervision between transmitter and receiver or between image input and image output device, e.g. between a still-image camera and its memory or between a still-image camera and a printer device
  • H04N2201/333—Mode signalling or mode changing; Handshaking therefor
  • H04N2201/33307—Mode signalling or mode changing; Handshaking therefor of a particular mode
  • H04N2201/33342—Mode signalling or mode changing; Handshaking therefor of a particular mode of transmission mode
  • H04N2201/33357—Compression mode
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W76/00—Connection management
  • H04W76/10—Connection setup
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
  • H04W88/14—Backbone network devices

Definitions

• T e present invention relates to facsimile communications over wireless links. and. more particularly, to facsimile (fax) communications over an analog cellular communications channel.
• AMPS Advanced Mobile Phone Service
• fax communications can take place over an AMPS cellular communications channel
• AMPS cellular communications channel there are some "idiosyncrasies" of fax communications over an AMPS cellular channel that affect the reliability of a fax/cellular connection (hereafter referred to as cellular fax)
• a fax receiver provides "delayed feedback" on any error detection and correction to a corresponding fax transmitter.
• This "delayed feedback” is due, in part, to the fact that fax handshaking and modulation schemes are "half-duplex," and also because of fax error correcting requirements like the "Error Correction Mode” (ECM) as defined in International Telecommunication Union (ITU) fax standards like T 4 (fax encoding standard) and T.30 (fax handshaking procedures).
• ECM Error Correction Mode
• transmission of error information from a fax receiver to the corresponding fax transmitter is delayed until after 255 frames of fax information are received
• the effect of this "delayed feedback" is that a cellular fax call generally takes longer to complete than when only land-line connections are involved.
• the cellular fades and hits which characterize the impairments of the cellular communications channel, can cause a loss of carrier or a large burst of errors.
• a fax modem generally speaking, is not tolerant to bad line conditions and will tend to immediately disconnect if the received signal quality is not good. Consequently, cellular fades and hits may cause a fax modem to abruptly disconnect.
• the problems to solve in sending fax over cellular communications channels are enhance the quality of the receiv ed fax, l e., lower the Bit Error Rate (BER), enhance the reliability of the fax transfer, I e . reduce the number of abrupt disconnects, and enhance the overall speed, or throughput, of the fax transfer
• BER Bit Error Rate
• fax-capable terminal equipment at the mobile end of the cellular fax call transmits fax information in digital form over a full-duplex digital cellular channel to a far-end fax-capable modem in a Mobile Switching Center (MSC).
• MSC Mobile Switching Center
• the far-end fax-capable modem then establishes the traditional analog-based fax call over the land-line portion of the cellular fax call
• the fax-capable terminal equipment at the mobile end communicates directly with the far-end fax-capable modem in the MSC since there is no analog modem at the cellular end
• a cellular modem enters an extended-mode of operation in which some modem-commands are classified as local or remote Local commands are operated on by the cellular modem, while remote commands are transmitted to a far-end endpoint
• a far-end endpoint This allows fax-capable terminal equipment at the mobile end of the connection to communicate directly with a far-end fax-capable modem in the MSC notwithstanding the presence ot an analog cellular modem at the mobile end
• a cellular modem is configured in one of two modes of operation a data mode or a fax mode
• the cellular modem completes all calls as in the p ⁇ or art.
• fax information is transmitted over a cellular-portion of the cellular fax call using a "2-D" fax compression scheme and a data modulation as specified in AT&T Paradyne's "Enhanced Throughput Protocol " (ETC)
• ETC Enhanced Throughput Protocol
• "AT-commands" related to establishing the fax connection are transmitted from the cellular modem to an MSC that includes a cellular modem pool
• the latter comprises a number of pairs of modems in which the data terminal equipment (DTE) ports of each modem pair are cross-connected in a "back-to- back” fashion This allows the two modems of each pair to interchange data ⁇ ia their DTE ports and therebv isolate that portion of the cellular fax call over the cellular communications channel from that portion of the cellular fax
• FIG 1 shows an illustrative high-level block diagram of a cellular communications system embodying the principles of the invention
• FIG 2 shows a more detailed block diagram of the cellular communications system of FIG 1 .
• FIG 3 shows a flow diagram for processing a fax call in accordance with the p ⁇ nciples of the invention
• FIG 4 shows an illustrative flow diagram for use in a PSTN-side modem of the cellular modem pool shown in FIG 2
• FIG 5 shows an illustrative block diagram of a modem for use in the cellular communications system of FIG 2
• FIG 6 shows an illustrative flow diagram in accordance with the principles of the invention for use in a cellular modem
• FIG 7 shows another illustrative flow diagram for processing a fax call in accordance with the p ⁇ nciples of the invention
• fax transmission is governed by a number of standards
• ITU V 17 defines half-duplex 14 4 kbps modulation
• ITU V 29 defmes half-duplex 9 6 kbps modulation
• ITU V 27ter defines half-duplex 4 8 kbps modulation
• ITU T 4 defines the fax image encoding scheme, generally know as Group 3
• Most fax equipment or services currently provided are Group 3 faxes Group 2 and Group 1 fax schemes, as specified by ITU T 3 and T 2, respectively, are much older, slower and simpler
• Group 3 fax is assumed
• ITU V 21 channel 2 specifies a 300 bps frequency-shift-keying (FSK) modulation used du ⁇ ng fax handshaking procedures, which is specified in ITU T 30
• FSK frequency-shift-keying
• two fax standards define the "class of fax equipment by specifying the distribution of fax functionalitv between the DTE and data communications equipment (DCE)
• DCE data communications equipment
• EIA/TIA-578 defines Class 1 fax where the DTE is responsible for providing ITU T 30 and T 4 functionality, while the DCE does the modulation, etc
• standard EIA/TIA-592 defines Class 2 fax, where the DTE is responsible for ITU T 4 only, while the DCE provides ITU T 30 functionalitv in addition to the modulation, etc
• tax Class 2 is assumed
• the DTE which is responsible for ITU T 4 functionality, determines the type of fax encoding, or fax compression, scheme by negotiating with the opposite fax endpoint durmg the above-mentioned handshaking
• One tvpe of fax encoding, or fax compression is termed "1-D,” which compresses one line at a time of an image, or document
• Another type of fax compression is termed "2-D,” which processes multiple lines of an image, or document
• "2-D" fax encoding compresses information on a current line of the document by taking into account what has changed from the previous line of the document Generally speaking, a 30 to 40% increase in data throughput occurs when using "2-D" fax encoding
• a fax DTE negotiates with an opposite fax DTE to determine the type of fax encoding to use
• a cellular modem enters an extended-mode of operation in which some modem- commands are classified as local or remote Local commands are operated on bv the cellular modem, while remote commands are stored and later transmitted to a far-end endpoint
• some modem- commands are classified as local or remote Local commands are operated on bv the cellular modem, while remote commands are stored and later transmitted to a far-end endpoint
• FIG 1 An illustrative high-level block diagram of a cellular communications system embodying the principles of the invention is shown in FIG 1
• a cellular fax call has already been established between the cellular fax endpoint, as represented by DTE 10 and cellular modem 100, and the PSTN fax endpoint as represented by DTE 30 and PSTN modem 300
• DTE 10 and cellular modem 100 the PSTN fax endpoint
• PSTN modem 300 PSTN modem
• PSTN user is associated with the PSTN fax endpoint
• DTE 10 is a personal computer, e g., a laptop, configured with fax application software 15 that is capable of transmitting or receiving fax information via line 1 1 , which is coupled to cellular modem 100
• DTE 30 is also representative of a personal computer
• the combination of a modem and DTE, e g , PSTN modem 300 and DTE 30, can equivalently represent a fax machine with an integrated modem
• the cellular fax call will be described in the context of transmitting fax information, e g , document 12, from DTE 10 to DTE 30
• the inventive concept also applies to a call originating from a point withm the PSTN network to a cellular endpoint
• fax application software 15 executing in DTE 10 is independently configured of the opposite fax endpoint to produce a higher-level compression bit map of an image, or document, that is to be transmitted by fax
• fax application software 15 is approp ⁇ ately modified to always perform "2-D" fax encoding of a fax document, or image, as represented by document 12, independent of the encoding of the opposite fax endpoint
• This can accomplished, for example, by providing a configuration option in fax application software 15 to either negotiate the fax encoding (as performed in the p ⁇ or art) or to simply specify the type of fax encoding
• fax application software 15 is configured to only perform "2-D" fax encoding
• fax application software 15 of DTE 10 provides an encoded fax signal representing "2-D" fax encoding to cellular modem 100 via line 1 1
• the latter represents the signaling, electronics, and wiring, for conforming to a DTE/DCE interface
• Cellular modem pool 230 receives the "2-D" fax encoded signal
• Cellular modem pool 230 comp ⁇ ses a number of pairs of back-to-back modems (desc ⁇ bed below )
• the use of cellular modem pool 230 allows the cellular-side of the cellular fax call to communicate data using the above-mentioned ETC protocol and the PSTN-side of the cellular fax call to use a traditional fax protocol like ITU V 17
• Cellular modem pool 230 performs a "2-D" to "1 -D” conversion to transmit a "1-D" fax encoded signal using a standard fax modulation over PSTN channel 340' (desc ⁇ bed below) to PSTN modem 200
• the latter recovers the "1-D” fax encoded signal and provides this signal to DTE 30, which, using fax application software 35, recovers document 12' It should be noted that no modification to the equipment of the PSTN fax endpoint is required
• DTE 10 provides a "2-D" fax encoded signal via line 1 1 to cellular modem 100 The latter provides a modulated data signal for transmission to mobile phone 140, via line 133 As known in the art.
• line 133 may include an RJl 1 adapter for coupling the DCE interface of cellular modem 100 to the local signaling interface of the mobile phone
• the cellular transceiver (not shown) of mobile phone 140 further modulates the signal provided by cellular modem 100 onto a cellular earner, which is transmitted to cell site transceiver 255, via impaired channel 200
• Cell site transceiver 255 demodulates the received cellular signal to provide a received digital version of the modulated data signal to MSC 250 via line 256 which is typicaliv a Tl faci tv
• MSC 250 includes switching system 245 and cellular modem pool 230 The latter comp ⁇ ses a number of pairs of back-to-back modems as represented by modem pair 225 As known in the art.
• switching system 245 provides the received digital version of the modulated data signal to modem pair 225 ot cellular modem pool 230 via line 236
• Modem pair 225 converts the "2-D" fax encoded signal provided by DTE 10 to a 1 -D" fax encoded signal and provides a modulated fax signal for transmission over the PSTN portion of the cellular fax call
• Modem pair 225 provides this modulated fax signal to the PSTN portion of the cellular fax call via line 241
• the PSTN portion of the cellular fax call is represented by PSTN facility 341 , PSTN 340, and line 31 1 , which represents the local-loop coupling PSTN modem 300 to a local exchange carrier (not shown ) mcluded within PSTN 340
• lines 236 and 241 have been
• cellular-side modem 235 and cellular modem 100 terminate the cellular portion of the cellular fax call while PSTN-side modem 240 and modem 300 terminate the PSTN portion of the cellular fax call
• PSTN-side modem 240 and modem 300 terminate the PSTN portion of the cellular fax call
• fax apphcation software 15 starts the fax call by sending a sequence of "AT-type commands" to cellular modem 100 This initial sequence of commands refers to the "setup" portion of the subsequent fax call
• cellular modem 100 buffers this setup sequence of "AT-type commands” and spoofs fax apphcation software 15 in step 595 That is, cellular modem 100 provides the necessary responses to fax application software 15 just like a regular fax call was being initiated notwithstanding the fact that cellular modem 100 is only buffe ⁇ ng these "AT-type commands" for latter transmission It is assumed that an appropriate buffer is included within cellular modem 100 to provide this storage
• the cellular user initiates a cellular fax call to the opposite PSTN fax endpoint
• the cellular user dials both an access code, e g , "*FAX " and a telephone number associated with the called party, who is represented by the PSTN fax endpoint
• the cellular user enters the well-known "AT dialing command," via DTE 10, using fax application software 15
• cellular modem 100 switches into a fax mode of operation in step 605
• a cellular modem embodying the principles of this invention can transition to a fax mode of operation upon detection of FAX-specific " AT command" parameters For example, even a pre-stored telephone number within the modem could be associated with
• MSC 250 does not provide a transparent call progress feature that allows the cellular user to hear the call progress on the PSTN-side of the cellular fax connection
• a transparent call progress feature is desc ⁇ bed in the co- pendmg, commonly assigned, U S Patent application of Exner et al entitled "Transparent Call Progress," Serial No 08/380872, filed on January 30, 1995 If a mobile switching center does provide a transparent call progress feature then it is assumed that the mobile switching center is appropriately modified so that a cellular user can enable or disable this feature on a per-call basis, e g , by entering a predefined special (*) code as is known in the art, e g , as is currently done to enable and disable call-waiting notification
• switching system 245 detects the "*FAX” access code and switches the incoming call through cellular modem pool 230
• "*FAX” is similar to "*DATA," as currently used, to alert switching system 245 to use the cellular modem pool
• switching system 245 selects an idle back-to-back modem pair of cellular modem pool 230 and assigns time slots as represented by lines 236 and 241 to the selected modem pair
• the selected pair of back-to- back modems is represented by modem pair 225
• switching system 245 provides a six digit code to modem pair 225 via line 236
• this six digit code is a reference number, e g , a pointer, associated with the actual telephone number, which is stored within switching system 245
• this six digit code is represented by the well-known "multi-frequency" (MF) signaling, l e .
• MF multi-frequency
• each digit is represented by a different set of frequency pairs
• cellular-side modem 235 converts the MF signal sequence to a data string, which, in this example, represents the six digit code
• Cellular- side modem 235 temporarily stores the six digit code in a buffer (not shown) in step 620
• cellular-side modem 235 begins training with cellular modem 100
• cellular modem 100 negotiates a data modulation and provides a "fax mode handshaking signal.” e g . a tone. to cellular-side modem 235 in step 630, l e , an "extended fax calling tone " The latter indicates that the subsequent data connection will transport fax information
• step 635 cellular-side modem 235 monitors the handshaking for this "fax mode handshaking signal " If no "fax mode handshaking signal" is detected, cellular-side modem 235 switches to data mode in step 640 However, if a "fax mode handshaking signal" is detected, cellular-side modem 235 switches to fax mode in step 645 In accordance with the invention, regardless of whether data mode or fax mode is selected, cellular-side modem 235 completes training in step 650 to subsequently communicate data over the cellular portion of the cellular fax call using a data modulation, e g , the above-mentioned ETC protocol As a result, du ⁇ ng the subsequent "message transmission" phase of the fax call, cellular-side modem 235 receives ITU T 4 data.
• a data modulation e g
• step 655. cellular-side modem 235 communicates call information with PSTN- side modem 240 by passing a predefined "AT-command" sequence that includes the above-described six digit code and identifies whether the call is a fax call or a data call.
• PSTN-side modem 240 similarly switches to a respective data mode or fax mode of operation in step 660
• PSTN-side modem 240 goes " off- hook” and regenerates the MF signal sequence on line 241 to dial the called party
• switching system 245 retrieves, and dials, the called party telephone number
• cellular modem 100 After completing training, cellular modem 100 provides a "connected" indication to DTE 10 and, in accordance with the inventive concept, sends the above-mentioned stored " 4T-type commands" representing setup information to the cellular-side modem in step 667 Also, because cellular modem 100 has switched to fax mode, cellular modem subsequently passes all FAX commands from DTE 10 to cellular-side modem 235 in step 670 once on-line Since DTE FAX commands are well-defined, cellular modem 100 transmits them as data directly to cellular-side modem 235 instead of operating on them In particular, in the fax mode, local "AT-commands" are operated on by the cellular modem, while remote commands are transmitted to a far-end endpoint In this context, all FAX commands from DTE 10 are classified as remote commands and are transmitted to cellular-side modem 235 in step 670 This allows fax-capable terminal equipment at the mobile end to communicate directly with far-end fax-capable PSTN modem 240
• PSTN-side modem 240 In the process of establishing the fax call, PSTN-side modem 240 not only performs (as in the p ⁇ or art) the fax handshaking with PSTN modem 300 but also monitors this control information to determine the type of fax encoding that is to be used As noted above, fax application software 15 always provides "2-D" fax encoded data Consequently, and in accordance with the principles of the invention, PSTN-side modem 240 translates the "2-D" fax encoded data into "1-D" fax encoded data if necessary This is shown in FIG 4, which illustrates a flow diagram for use within PSTN-side modem 240 In step 700, PSTN-side modem 240 monitors the above-mentioned fax handshaking between DTE 10 and DTE 30 to determine the level of fax compression negotiated over the PSTN portion of the cellular fax call If the level of fax compression is "1 -D " then PSTN-side modem 240 additionally translates the T 4 encode
• PSTN-side modem 240 is not run-time challenged in performing the translation of step 710 since it is not doing more complex data modulations like V 42b ⁇ s, V 42, etc That is.
• PSTN-side modem 240 has enough run time available to do the "2-D" to "1-D" compression translation
• the corresponding fax transmission would simply be slowed down Even in this latter scenario total throughput would still probably exceed the case where no "2-D" compression was used over the cellular portion of the cellular fax call
• the cellular link is generally more impaired than the PSTN link, the cellular link, normally, will be slower — 1 e , the cellular link will be the bottleneck Consequently, the PSTN-side modem is idle, waiting tor data, much of the time
• the PSTN-side modem can support 14,400 bps using ITU V 17, in comparison the cellular link may typically be at 4,800 bps using ETC
• FIG 5 shows an illustrative high-level block diagram of a modem in accordance with the principles of the invention
• modem 50 includes a microprocessor 80, memory 95, a digital signal processor 85, e g , for providing the tone generator/ detector and other modem functions mentioned above, and universai/asvnchronous receive transmit (UART) 75 for providing the DTE mterface
• Microprocessor 80 is coupled to DSP 85 via line 81 , which represents, address data control, and status leads
• line 81 represents, address data control, and status leads
• the portions of the flow chart of FIG 4 is a part of the program stored in memory 95 and executed by microprocessor 80 when FIG 5 represents cellular modem 100
• these portions of the flow chart referred to, and desc ⁇ bed earlier, are shown again in FIG 6
• a fax call comp ⁇ ses a setup (off ⁇ line) portion and an on-line portion, du ⁇
• step 668 In this "extended fax mode of operation," the fax call setup sequence is changed
• fax application software 15 first establishes the fax connection and then transmits the above-mentioned off-line "AT-type commands" to cellular modem 100
• steps 590 and 595 have been deleted and cellular modem 100 does not have to buffer the off-line "AT-type commands
• step 667 has been deleted and replaced by step 668, where the respective DTE equipment now sends the off-line "AT-type commands” after the call is setup
• This modification removes any additional buffering and the requirement for cellular modem 100 to spoof fax application software 15 during a portion of the fax call.
• the inventive concept was illustrated in the context of a personal computer and a distinct cellular modem, it should be realized that these can be integrated into one physical arrangement for the sending and receiving of faxes in accordance with the p ⁇ nciples of the invention Similarly, although described m the context of an additional compression feature, it should be realized that this is not required to provide an extended fax mode of operation Also, although desc ⁇ bed in the context of a data mode and a fax mode, it should be realized that the local and remote modes of operation can be user-definable For example, a local mode of operation can be associated with both a data mode and a standard fax mode in which data and fax calls, respectively, are completed as in the prior art However, in the remote mode of operation all FAX commands are transmitted to an opposite endpoint In this context, the modem can be switched into the remote mode by, e g , a suitably defined "AT-type ' command issued by a user via the associated data terminal equipment

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• Engineering & Computer Science (AREA)
• Signal Processing (AREA)
• Human Computer Interaction (AREA)
• Multimedia (AREA)
• Computer Networks & Wireless Communication (AREA)
• Facsimile Transmission Control (AREA)
• Facsimiles In General (AREA)

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• 1995
  • 1995-12-18 US US08/573,739 patent/US5752199A/en not_active Expired - Lifetime
• 1996
  • 1996-12-16 WO PCT/US1996/020053 patent/WO1997023103A1/en not_active Ceased
  • 1996-12-20 TW TW085115762A patent/TW318309B/zh active

Patent Citations (4)

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