U.S. patent number RE35,740 [Application Number 08/245,606] was granted by the patent office on 1998-03-03 for telecommunication system.
This patent grant is currently assigned to ECI Telecom Ltd.. Invention is credited to Joshua Piasecki, Sason Sourani.
United States Patent |
RE35,740 |
Piasecki , et al. |
March 3, 1998 |
Telecommunication system
Abstract
A telecommunication system for interconnecting a plurality of
telephone communication trunks to a transmission network, the
system including transmission apparatus at a first end of the
transmission network including apparatus for detecting facsimile
signals on the plurality of telephone communication trunks,
apparatus for demodulating the facsimile signals, apparatus for
transmitting along the transmission network, in demodulated form,
the facsimile signal output from the apparatus for demodulating,
and receiving apparatus at a second end of the transmission network
including apparatus for modulating the facsimile signals received
along the transmission network.
Inventors: |
Piasecki; Joshua (Ramat Gan,
IL), Sourani; Sason (Hod Hasharon, IL) |
Assignee: |
ECI Telecom Ltd. (Petach Tikva,
IL)
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Family
ID: |
11059738 |
Appl.
No.: |
08/245,606 |
Filed: |
May 19, 1994 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
451748 |
Dec 18, 1989 |
05117453 |
May 26, 1992 |
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Foreign Application Priority Data
Current U.S.
Class: |
379/100.01;
379/93.01 |
Current CPC
Class: |
H04J
3/172 (20130101); H04N 1/001 (20130101); H04N
1/00281 (20130101); H04N 1/33323 (20130101); H04N
1/33346 (20130101); H04N 19/90 (20141101); H04N
2201/3335 (20130101); H04N 2201/33364 (20130101) |
Current International
Class: |
H04N
1/00 (20060101); H04M 011/00 () |
Field of
Search: |
;379/100,98,97,93
;358/425 ;370/110.1,81 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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61-121634 |
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Jun 1986 |
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JP |
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61-198941 |
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Sep 1986 |
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JP |
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62-230130 |
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Oct 1987 |
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JP |
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63-26044 |
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Feb 1988 |
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JP |
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63-93238 |
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Apr 1988 |
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JP |
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64-81442 |
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Mar 1989 |
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JP |
|
Other References
Fascicle VIII.1--Rec. V. 29, 9600 Bits Per Second Modem
Standardized for Use on Point-to-Point 4-Wire Leased Telephone-Type
Circuits, (Geneva 1976; amended at Geneva, 1980 . . . Melbourne,
1988). .
Facicle VII.3--Rec. T.4, Standardization of Group 3 Facsimile
Apparatus for Document Transmission. (Geneva 1980, amended at
Malaga-Torremolinos, 1984 and Melbourne, 1988). .
Study Group XVIII--Report R 26(A), International Telegraph and
Telephone Consulatative Committee, 1985-1988, Aug. 1986, "Report of
the Geneva Meeting (8-15 Jul. 1986) . . . Part A". .
Integral Modems, Rockwell, R96DP 9600 BPS Data Pump Modem, Data
Sheet Order No. MD07, Mar., 1984 Document No. 29200N07. .
"An Unbeatable Combination of Speed, Size, Versatiltiy and Price",
Master Systems Brochure for the MS9600S, V29 9600 bps Modem. .
Master Systems Brochure, MS9600S, V29 9600 bps Modem. .
Craycom Brochure, MS 9600S, V29 9600bps Modem, Craycom Networking
by Design. .
Thorn EMI Datatech Brochure, 9648FT Modem, Thorn EMI
Datacomms--Placing the World at Your Fingertips. .
Musgrave, "Going for Speed", Datamation, Feb. 1987. .
"Breaking The Throughput Barrier: Which High-Speed Modems Test
Best", Data Communications, May 1988, Special Report. .
Dimolitsas et al., "Evaluation of ADPCM Coders for Digital Circuit
Multiplication Equipment", Comsat Technical Review, vol. 17, No. 2,
Fall 1987. .
Takebayashi et al., "A 32kbps ADPCM With Improvement in Coding
Characteristics for 9600bps Modem Signal", IEEE, 1986. .
Benvenuto et al., "Waveform Coding of 9.6 kb/s Voiceband Data
Signals at 32 kb/s", IEEE 1987. .
Artzt, "Duplex Transmission of Frequency-Modulated Sound and
Facsimile", RCA Review, vol. V1, No. 1, Jul. 1941. .
Kamae et al., "Experiments on Facsimile Intelligent Communication
System FICS-0", Review of the Electrical Communication
Laboratories, Nippon Telegraph and Telephone Public Corp., vol. 28,
Nos. 9-10, Sep./Oct./1980. .
Black, "PLC-1:A TASI System for Small Trunk Groups", IEEE
Transactions on Communications, vol. Com-30, No. 4, Apr., 1982.
.
Agrawal et al., "The Design of an ADPCM/TASI Sysem for PCM Speech
Compression", IEEE Transactions on Communications, vol. Com-29, No.
9, Sep., 1981. .
Chamzas et al., "Progressive Encoding of Facsimile Images Using
Edge Decomposition (PED)", GLOBECOM '88: IEEE Global
Telecommunications Conference . . . Information Age, Hollywood, FL,
Conference Record Nov./Dec./1988. .
Chamzas et al., "Encoding Facsimile Images for Packet-Switched
Networks", IEEE Journal of Selected Areas in Communications, vol.
7, No. 5, Jun. 1989, pp. 857-864. .
Johnsen et al., "Coding of Two-Level Pictures by Pattern Matching
and Substitution", The Bell System Technical Journal, vol. 62, No.
8, Oct. 1984, pp. 2513-2545. .
Mounts et al., "Some Extensions of the Ordering Techniques for
Compression of Two-Level Facsimile Pictures", The Bell System
Technical Journal, vol. 57, No. 8, Oct. 1978, pp. 3057-3067. .
Segen et al., "Facsimile Compression by Pattern Matching",
Proceedings--1982, IEEE Computer Society Conference on Pattern
Recognition and Image Processing, Las Vegas, NV, Jun. 1982,
Conference Record, pp. 191-196. .
Johnsen et al., "A Pattern Matching Technique for Facsimile
Coding", IEEE International Conference on Communications: ICC '82,
The Digital Revolution, Philadelphia, PA, Jun. 1982, Conference
Record, pp. 2G.2.1-2G.2.7..
|
Primary Examiner: Kuntz; Curtis
Assistant Examiner: Woo; Stella L.
Attorney, Agent or Firm: Cushman, Darby & Cushman
Claims
We claim:
1. A telecommunication system for interconnecting a plurality of
telephone communication trunks, carrying voice, facsimile and
non-facsimile voiceband data signals, to a transmission network,
said system comprising:
transmission means at at least a first end of said transmission
network including;
means for detecting facsimile signals, as distinguished from other
voiceband data signals, on said plurality of telephone
communications trunks;
means for demodulating only said facsimile signals;
means for transmitting along said transmission network, in
demodulated form, the facsimile signal output of the means for
demodulating; and
receiving means at at least a second end of the transmission
network including:
means for modulating said facsimile signals received along said
transmission network.
2. A telecommunication system according to claim 1 and wherein
said transmission means also comprises:
means for detecting other signals;
means for compressing said other signals; and
means for transmitting said other signals along said transmission
network; and
said receiving means also comprises:
means for receiving said other signals transmitted along the
transmission network; and
means for decompressing said other signals.
3. A telecommunication system according to claim 1 and wherein said
transmission means also comprising means for determining the mode
of operation of the detected facsimile signals.
4. A telecommunication system according to claim 2 and wherein said
transmission means also comprising means for determining the mode
of operation of the detected facsimile signals.
5. A telecommunication system according to claim 3 and wherein said
transmission means also comprises means for transmitting to said
receiving means over said transmission network an indication of the
mode of operation of the detected facsimile signals.
6. A telecommunication system according to claim 4 and wherein said
transmission means also comprises means for transmitting to said
receiving means over said transmission network an indication of the
mode of operation of the detected facsimile signals.
7. A telecommunication system according to claim 5 and wherein said
receiving means comprises means responsive to a received indication
of the mode of operation of the detected facsimile signals to cause
said means for modulating to operate in a corresponding mode of
operation.
8. A telecommunication system according to claim 6 and wherein said
receiving means comprises means responsive to a received indication
of the mode of operation of the detected facsimile signals to cause
said means for modulating to operate in a corresponding mode of
operation.
9. A telecommunication system according to claim 2 and wherein said
transmission means also comprises means for transmitting to the
receiving means an indication of the nature of the signals
transmitted thereby as facsimile signals or other signals.
10. A telecommunication system according to claim 9 and and wherein
said receiving means also comprises means for receiving said
indication of the nature of the signals and for causing the
operation of said means for modulating and said means for
decompressing accordingly.
11. A system according to claim 2 and wherein said other signals
comprise voice signals and voiceband data signals, said means for
compressing comprise means for compressing said voice signals and
means for compressing said voiceband data signals and said means
for decompressing comprise means for decompressing said voice
signals and means for decompressing said voiceband data
signals.
12. A system according to claim 9 and wherein said other signals
comprise voice signals and voiceband data signals, said means for
compressing comprise means for compressing said voice signals and
means for compressing said voiceband data signals and said means
for decompressing comprise means for decompressing said voice
signals and means for decompressing said voiceband data
signals.
13. A system according to claim 10 and wherein said other signals
comprise voice signals and voiceband data signals, said means for
compressing comprise means for compressing said voice signals and
means for compressing said voiceband data signals and said means
for decompressing comprise means for decompressing said voice
signals and means for decompressing said voiceband data
signals.
14. A system according to claim 1 and wherein said facsimile
signals are Group 3 facsimile signals.
15. A system according to claim 1 and wherein said means for
detecting the presence of facsimile signals comprises means for
detecting a sequence of flag characters in Group 3 facsimile binary
coded signaling signals.
16. A system according to claim 3 and wherein said means for
determining the mode of operation comprises:
a plurality of facsimile demodulators, each being programmed to
demodulate at least one expected modem signal according to the
Group 3 facsimile standard;
means for initially supplying meaning selected facsimile signals
simultaneously to said plurality of facsimile demodulators; and
means for determining which of said plurality of facsimile
demodulators initially successfully demodulates an incoming
selected facsimile signal.
17. A system according to claim 4 and wherein said means for
determining the mode of operation comprises:
a plurality of facsimile demodulators, each being programmed to
demodulate at least one expected modem signal according to the
Group 3 facsimile standard;
means for initially supplying incoming selected facsimile signals
simultaneously to said plurality of facsimile demodulators; and
means for determining which of said plurality of facsimile
demodulators initially successfully demodulates an incoming
selected facsimile signal.
18. A system according to claim 16 and wherein said means for
demodulating comprises:
means for utilizing the facsimile demodulator which initially
successfully demodulates an incoming selected facsimile signal for
continuing demodulation of said incoming selected facsimile
signal.
19. A system according to claim 17 and wherein said means for
demodulating comprises:
means for utilizing the facsimile demodulator which initially
successfully demodulates an incoming selected facsimile signal for
continuing demodulation of said incoming selected facsimile
signal.
20. A system according to claim 16 and wherein said plurality of
facsimile demodulators include V.29, V.21 and V.27
demodulators.
21. A system according to claim 17 and wherein said plurality of
facsimile demodulators include V.29, V.21 and V.27
demodulators.
22. A system according to claim 20 and and also comprising a buffer
providing a predetermined delay for receiving the outputs of said
plurality of facsimile demodulators and wherein positive
identification of the transmission rate of a V.27 modem signals by
a V.27 demodulator takes place after said predetermined delay.
23. A system according to claim 21 and and also comprising a buffer
providing a predetermined delay for receiving the outputs of said
plurality of facsimile demodulators and wherein positive
identification of the transmission rate of a V.27 modem signal by a
V.27 demodulator takes place after said predetermined delay.
24. A system according to claim 22 and wherein upon detection of a
V.27 modem carrier but before positive identification of its
transmission rate, said buffer is operative to transmit at least
part of said V.27 modem carrier.
25. A system according to claim 23 and wherein upon detection of a
V.27 model carrier but before positive identification of its
transmission rate, said buffer is operative to transmit at least
part of said V.27 modem carrier.
26. A system according to claim 1 and wherein said demodulating
means comprises facsimile signal demodulator and forward error
correction means wherein said forward error correction means are
operative to protect the output of said facsimile demodulator.
27. A telecommunication compressing system for interconnecting a
first plurality of telephone communication channels, carrying
voice, facsimile and non-facsimile voiceband data signals, to a
transmission network comprising a second plurality of transmission
channels, said system comprising:
transmission means at at least a first end of said transmission
network including:
means for detecting signals on said first plurality of telephone
communication channels and means for assigning each telephone
communication channel to an available one of the second plurality
of transmission channels;
means for classifying said signals on said first plurality of
telephone communication channels at least as selected facsimile
signals and other signals;
first means for demodulating only said selected facsimile signals,
as distinguished from other voiceband data signals;
second means for compressing said other signals;
means for connecting said demodulated facsimile signals and said
compressed other signals to the second plurality of transmission
channels;
means for communicating the assignment and the classification of
said signals on said second plurality of transmission channels
along said transmission network;
receiving means at at least a second end of the transmission
network including:
means for receiving communications from said means for
communicating for determining the assignment and the classification
of said second plurality of signals received along said
transmission network;
third means for modulating said selected facsimile signals received
along said transmission network;
fourth means for decompressing said other signals received along
said transmission network; and
means for connecting said signals on said second plurality or
transmission channels to said third means for modulating and said
fourth means for decompressing according to the classification
thereof of said signals.
28. A system according to claim 1 and wherein said means for
detecting facsimile signals is operative for detection of facsimile
signals including signals which do not conform to CCITT
recommendation T.30.
29. A system according to claim 2 and also comprising means
responsive to said means for detecting facsimile signals and to
said means for detecting other signals for switching signals
received along the telephone communication trunks to either said
means for demodulating facsimile signals or to said means for
compressing other signals.
30. A system according to claim 29 and wherein said means for
switching is operative during a silent period occurring during
facsimile "handshake".
31. A system according to claim 29 and wherein said switching means
is operative to switch signals received along the telephone
communication trunks to said means for compressing other signals
when said plurality of facsimile demodulators fail to make a
positive identification of a facsimile signal over a predetermined
interval. .Iadd.
32. A telecommunication system for interconnecting a plurality of
telephone communication trunks, carrying voice, facsimile and
non-facsimile voiceband data signals to a transmission network, the
system comprising:
a transmitter at at least a first end of the transmission network
including:
at least one detector which receives signals from said plurality of
communication trunks and which detects facsimile signals thereon,
as distinguished from other voiceband data signals by detecting a
signal unique to facsimile signals;
at least one demodulator which receives facsimile signals and
demodulates at least some of the facsimile signals detected by the
detector to produce demodulated facsimile signals; and
an interface which receives the demodulated facsimile signals and
transfers them to the transmission network. .Iaddend..Iadd.33. A
system according to claim 32 and further comprising:
a receiver at at least a second end of the transmission network
including:
a modulator which receives demodulated facsimile signals
transmitted along the transmission network and modulates them to
produce voiceband facsimile signals. .Iaddend..Iadd.34. A system
according to claim 32, wherein the demodulator is operative to
demodulate only facsimile signals. .Iaddend..Iadd.35. A system
according to claim 32, wherein the detector detects a signal
sequence characteristic of a plurality of facsimile modes of
operation. .Iaddend..Iadd.36. A system according to claim 32
wherein the demodulator comprises:
a plurality of facsimile demodulators which receive a detected
facsimile signal, each facsimile demodulator being programed to
demodulate said facsimile signal according to a predetermined
facsimile mode;
a second detector which receives the outputs of said facsimile
detectors and detects which of the plurality of facsimile
demodulators successfully
demodulates an incoming facsimile signal. .Iaddend..Iadd.37. A
system according to claim 36 wherein the plurality of facsimile
demodulators includes V.29, V.21 and V.27 demodulators.
.Iaddend..Iadd.38. A system according to claim 37 and also
comprising a buffer providing a predetermined delay for receiving
the outputs of said plurality of facsimile demodulators and wherein
positive identification of the transmission rate of a V.27 modem
signal by a V.27 demodulator takes place after said predetermined
delay. .Iaddend..Iadd.39. A system according to claim 38, wherein
upon detection of a V.27 modem carrier but before positive
identification of its transmission rate, said buffer is operative
to transmit at least part of the V.27 modem carrier.
.Iaddend..Iadd.40. A system according to claim 32 wherein the
transmission system also includes: a signal compressor which
compresses signals other than those detected by said detector, and
wherein said interface transmits said other signals along said
transmission network. .Iaddend..Iadd.41. A system according to
claim 40 and also comprising:
a switch, responsive to the detector, which switches signals
received along the telephone communication trunks to either said
demodulator or said compressor. .Iaddend..Iadd.42. A system
according to claim 36 and also comprising:
a switch, responsive to the detector, which switches signals
received along the telephone communication trunks to either said
demodulator or said compressor. .Iaddend..Iadd.43. A system
according to claim 42 wherein said switch is operative to switch
said detected signals to said compressor when the second detector
fails to make positive identification of the mode
of a facsimile signal during a predetermined interval.
.Iaddend..Iadd.44. A system according to claim 43 wherein said
switch is operative to switch signals to said means for
demodulating only during a silent period occurring during facsimile
handshake. .Iaddend..Iadd.45. A system according to claim 40
wherein:
the compressor is operative to compresses said other signals in
accordance with their classification; and
the transmitter is operative to transmit said classification of the
signals on the transmission network. .Iaddend..Iadd.46. A system
according to claim 32, wherein the transmission network comprises a
plurality of transmission channels, and further comprising:
a router which assigns at least one of the signals received by the
transmission system from the plurality of communication trunks to
one of the transmission channels, wherein the transmitter
communicates the assignment and optionally other information
regarding the signals along the transmission network.
.Iaddend..Iadd.47. A method for interconnecting a plurality of
telephone communication trunks carrying voice, facsimile and
non-facsimile voiceband data signals, to a transmission network,
the method comprising:
detecting facsimile signals, as distinguished from other voiceband
data signals received from the plurality of telephone communication
trunks;
demodulating only detected facsimile signals to form demodulated
facsimile signals; and
transmitting the demodulated facsimile signals along the
transmission network. .Iaddend..Iadd.48. A method according to
claim 47 wherein the detection of the facsimile signals comprises
detecting a signal sequence characteristic of a plurality of
facsimile modes of operation. .Iaddend..Iadd.49. A method according
to claim 47 wherein modulating only detected facsimile signals
comprises determining the mode of operation of
the detected facsimile signals. .Iaddend..Iadd.50. A method
according to claim 49 wherein the determination of the mode of
operation comprises:
supplying an incoming detected facsimile signal simultaneously to a
plurality of facsimile demodulators, each being programed to
demodulate at least one expected modem signal according to a
facsimile mode; and
determining which of the plurality of facsimile demodulators
successfully demodulates an incoming selected facsimile signal.
.Iaddend..Iadd.51. A method for interconnecting a plurality of
telephone communication trunks carrying voice, facsimile and
non-facsimile voiceband data signals, to a transmission network,
the method comprising:
detecting facsimile signals, as distinguished from other voiceband
data signals received from the plurality of telephone communication
trunks by detecting a signal sequence characteristic only of
facsimile signals;
demodulating at least some of said detected facsimile signals to
form demodulated facsimile signals; and
transmitting the demodulated facsimile signals along a transmission
network. .Iaddend..Iadd.52. A method according to claim 51 wherein
the detection of the facsimile signals comprises detecting a signal
sequence characteristic of a plurality of facsimile modes of
operation. .Iaddend..Iadd.53. A method according to claim 51
wherein modulating only detected facsimile signals comprises
determining the mode of operation of the detected facsimile
signals. .Iaddend..Iadd.54. A method according to claim 53 wherein
the determination of the mode of operation comprises:
supplying an incoming detected facsimile signal simultaneously to a
plurality of facsimile demodulators, each being programed to
demodulate at least one expected modem signal according to a
facsimile mode; and
determining which of the plurality of facsimile demodulators
successfully
demodulates an incoming selected facsimile signal.
.Iaddend..Iadd.55. A telecommunication system for interconnecting a
plurality of telephone communication trunks, carrying voice,
facsimile and non-facsimile voiceband data signals to a
transmission network, the system comprising:
a transmitter at at least a first end of the transmission network
including:
a demodulator which receives facsimile signals and demodulates at
least some of the facsimile signals to produce demodulated
facsimile signals, including:
a plurality of facsimile demodulators which receive a detected
facsimile signal said plurality of facsimile demodulators being
programed to demodulate said facsimile signal according to
different predetermined facsimile modes; and
a detector which receives the outputs of said plurality of
facsimile demodulators and detects which of the plurality of
facsimile demodulators successfully demodulates an incoming
facsimile signal; and
an interface which receives the demodulated facsimile signals and
transfers them to the transmission network. .Iaddend..Iadd.56. A
system according to claim 55 wherein the plurality of facsimile
demodulators includes V.29, V.21 and V.27 demodulators.
.Iaddend..Iadd.57. A system according to claim 55 and also
comprising a buffer providing a predetermined delay for receiving
the outputs of said plurality of facsimile demodulators and wherein
positive identification of the transmission rate of a V.27 modem
signal by a V.27 demodulator takes place after said predetermined
delay. .Iaddend..Iadd.58. A system according to claim 57, wherein
upon detection of a V.27 modem carrier but before positive
identification of its transmission rate, said buffer is operative
to transmit at least part of the V.27 modem carrier.
.Iaddend..Iadd.59. A system according to claim 55 and also
including a facsimile detector which receives signals from said
plurality of communication trunks and which detects facsimile
signals thereon, as distinguished from other voiceband data signals
by detecting a
signal unique to facsimile signals. .Iaddend..Iadd.60. A system
according to claim 59 wherein said facsimile detector is operative
for detection of facsimile signals which do not conform to CCITT
recommendation T.30. .Iaddend..Iadd.61. A telecommunication system
for interconnecting a plurality of telephone communication trunks,
carrying voice, facsimile, and non-facsimile voiceband data signals
to a transmission network, the system comprising:
a transmitter at at least a first end of the transmission network
including:
at least one detector which receives signals from said plurality of
communication trunks and which detects facsimile signals thereon,
as distinguished from other voiceband data signals;
at least one demodulator which receives facsimile signals and
demodulates only facsimile signals detected by the detector to
produce demodulated facsimile signals; and
an interface which receives the demodulated facsimile signals and
transfers them to the transmission network. .Iaddend.
Description
FIELD OF THE INVENTION
The present invention relates to communications apparatus generally
and more particularly to telecommunication systems with facsimile
demodulation and modulation capabilities.
BACKGROUND OF THE INVENTION
Various types of telecommunication systems for interconnecting
telephone communication trunks to a transmission network are known
in the patent literature and in the marketplace. One type of such
apparatus is known as Digital Circuit Multiplication Equipment
systems which typically include Time Assignment Speech
Interpolation (TASI) Apparatus. There is described in applicant's
European Patent and in applicant's U.S. Pat. No. 4,523,309, TASI
apparatus which has gained widespread market acceptance.
A particular feature of the abovementioned U.S. Pat. No. 4,523,309
is that control information such as the assignment, synchronization
and identification information is transmitted along the
communication channels instead of on separate signaling channels as
in the prior art. In addition, the signaling communication channel
assignment information is also supplied via the voice channels
rather than via the signaling channels.
Another type of telecommunication system for interconnecting
telephone communication trunks to a transmission network is
described in a paper by R. W. Muise et al entitled "Experiments in
Wideband Packet Technology," given at the International Zurich
Seminar on Digital Communication, April, 1986. The paper discloses
a system which comprises an access interface and a wideband packet
switch for sending packets of speech and data across a transmission
network.
There are known Digital Circuit Multiplication Equipment (DCME)
systems in which the advantages of Digital Speech Interpolation
(DSI) and adaptive pulse code modulation (ADPCM) compression
techniques have been incorporated, as demonstrated in applicant's
U.S. Pat. No. 4,747,096 which also uses voice channels for the
transmission of control information. In addition, the system
detects voiceband data transmission and compresses it according to
an optimal ADPCM adapted for voiceband data.
However, the optimal ADPCM adapted for voiceband data compresses
the voiceband data at a 2:1 rate whereas the compression rate of
the DSI and the ADPCM for speech is 6:1. Thus, with the current
proliferation of personal facsimile machines whose signals when
transmitted via a DCME are compressed as voiceband data, the
overall compression rate of a DCME is approaching 3:1.
In a Delayed Contribution D.788/XVIII presented at the CCITT
Working Party XVIII/8 in Geneva Switzerland on Jul. 8-15, 1986 by
EUTELSAT entitled "EUTELSAT Considerations on LRE-DSI
characteristics for Digital Circuit Multiplication", there appears
a proposal to demodulate V.29 voice band data signals in order to
enable such signals to be transmitted via a compression system
which employs ADPCM encoding for signal compression. This reference
only proposes V 29 modem demodulation in DCME but does not explain
how to do it. Importantly, it does not teach how to detect
facsimile signals for subsequent demodulation thereof.
In a Final Report submitted to the International Maritime Satellite
Organization (INMARSAT) entitled "Study of Facsimile Interface
Units for Future Inmarsat Digital Communications System" dated Jul.
28, 1988 there is proposed a concept for demodulation of an
all-facsimile channel. No consideration is given to detection of
facsimile signals on a "mixed" channel which carries both speech
and facsimile signals, and switching between different processing
routes for facsimile and speech in response to such detection.
Furthermore, this reference does not deal with many facsimile
protocols which are in common use in such "mixed" channels.
SUMMARY OF THE INVENTION
The present invention seeks to provide a telecommunication system
with improved facsimile signal compression capabilities.
There is thus provided in accordance with a preferred embodiment of
the invention a telecommunication system for interconnecting a
plurality of telephone communication trunks to a transmission
network, the system comprising transmission apparatus at at least a
first end of the transmission network and receiving apparatus at at
least a second end of the transmission network. The transmission
apparatus includes apparatus for detecting signals on the plurality
of telephone communication trunks and classifying the signals at
least as selected facsimile signals and other signals, first
apparatus for demodulating the selected facsimile signals, second
apparatus for compressing the other signals, and apparatus for
communicating the nature of signals transmitted along the
transmission network. The receiving apparatus includes apparatus
for receiving communications from the apparatus for communicating
for determining the nature of signals received along the
transmission network, third means for modulating the selected
facsimile signals received along the transmission network, and
fourth means for decompressing the other signals received along the
transmission network.
It is understood that the demodulation and modulation may be
complete including, for example, descrambling and scrambling, or
incomplete not including scrambling and descrambling.
Additionally, in accordance with a preferred embodiment of the
invention the other signals comprise voice signals and voiceband
data signals. The second apparatus comprises both apparatus for
compressing the voice signals and apparatus for compressing the
voiceband data signals. The fourth apparatus comprises both
apparatus for decompressing the voice signals and apparatus for
decompressing the voiceband data signals.
Further, in accordance with a preferred embodiment of the invention
the selected facsimile signals are Group 3 facsimile signals.
Still further, in accordance with a preferred embodiment of the
invention the apparatus for detecting and classifying includes
apparatus for detecting signal activity, apparatus for detecting
the presence of voiceband data signals and apparatus for detecting
the presence of group facsimile signals, comprising apparatus for
detecting a sequence of flag characters.
In accordance with a preferred embodiment of the invention the
demodulating apparatus comprises a plurality of facsimile
demodulators, each having a different mode of operation
corresponding to a group 3 facsimile signal, apparatus for
initially supplying incoming selected facsimile signals
simultaneously to the plurality of facsimile demodulators,
apparatus for determining which of the plurality of facsimile
demodulators initially successfully demodulates an incoming
selected facsimile signal, and apparatus for utilizing the
facsimile demodulator which initially successfully demodulates an
incoming selected facsimile signal for continuing demodulation of
the incoming selected facsimile signal. Since there are many
facsimile transmissions which do not adhere to the standard
protocol definitions as defined in CCITT Red Book Rec. T.50, the
data rate and mode of operation of the incoming facsimile signal
cannot be derived from a protocol analysis. It is an object of the
present invention to provide facsimile signal classification by
waveform analysis, rather than protocol analysis. Thus, at the
beginning of each facsimile signal burst, a plurality of facsimile
demodulators are needed to simultaneously demodulate the incoming
facsimile signals.
Additionally, in accordance with a preferred embodiment of the
invention the demodulating apparatus comprises facsimile signal
demodulator and forward error correction apparatus wherein the
forward error correction apparatus is operative to protect the
output of the facsimile demodulator.
An object of the present invention is to provide a facsimile signal
compression ratio between 4:1 and 6:1, a ratio much higher than
that achievable by treating facsimile transmissions a voiceband
data signals. The present invention achieves the desired
compression ratio by demodulating facsimile modem signals and
transmitting that information in binary data form to the far end
terminal where the original facsimile mode signal is
reproduced.
BRIEF DESCRIPTION OF THE DRAWINGS
The present invention will be understood and appreciated more fully
from the following detailed description taken in conjunction with
the drawings in which:
FIG. 1 is a functional block diagram illustration of the transmit
side and the receive side of the system showing graphically
functions of the international telephone multiplication system,
including the facsimile signal compression functions, constructed
and operative in accordance with a preferred embodiment of the
present invention;
FIGS. 2A and 2B, are block diagram illustrations of elements of the
transmit circuitry constructed and operative in accordance with a
preferred embodiment of the present invention;
FIG. 3 is a block diagram illustration of the facsimile demodulator
useful in the apparatus of FIGS. 2A and 2B;
FIGS. 4A and 4B are block diagram illustrations of elements or the
receive circuitry constructed and operative in accordance with a
preferred embodiment of the present invention;
FIG. 5 is a block diagram illustration of the facsimile modulator
useful in the apparatus of FIGS. 3A and 3B; and
FIG. 6 is a block diagram illustration of the signal flow from a
facsimile machine, through local telephone lines, to a switching
center useful in understanding the system of FIG. 1.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
Reference is now made to FIG. 6 which illustrates the data flow
from a facsimile machine through a local telephone system to a
transmission network. A facsimile machine 10, according to CCITT
Red Book, Malaga-Torremolinos 1984, Recommendations T.4 and T.30,
comprises a facsimile scanner and encoder 12, according to CCITT
Red Book Recommendation T.4, which produces a binary bit stream, at
rates up to 9.6 kbit/s, representing a compressed version of the
scanned page, and a modulator 14, such as the R96MFX Monofax by
Rockwell International, which modulates the binary bit stream onto
an analog waveform for transmission through local analog telephone
systems.
The Group 3 facsimile call procedure is defined in detail in CCITT
Red Book Rec. T.30. Typically, the facsimile call begins with a
2100 Hz. tone from the called terminal, followed by a coordination
dialog between the two facsimile machines at a rate of 300 bit/s,
modulated according to CCITT Red Book Rec. V.21, channel 2. The
facsimile messages are transmitted, page by page, at data rates of
2400, 4800, 7200, and 9600 bit/s, modulated according to CCITT Red
Book Rec. V.27 ter for the two lower rates and according to CCITT
Red Book Rec. V.29 for the two upper rates. It should be noted that
CCITT Red Book Rec. T.30 also allows for non-standard 300 bit/s
protocols.
An analog to digital (A/D) converter 16 receives the analog
waveform and samples the signal in order to transform it to a
standard 64 kbit/s pulse code modulated (PCM) digital signal. The
digital PCM signal is then transmitted, as one time slot or a 2.048
or a 1.544 Mbit/s signal, via a digital exchange 18, such as the
4ESS from AT&T, which may subsequently transmit it to a
transmission system, such as is described hereinbelow. It should be
noted that the digital signal produced by the facsimile scanner 12
is a binary data signal and the digital signal produced by the A/D
converter 16 is in the form of digital samples of an analog
waveform. The two rates are significantly different (up to 9.6
kbit/s vs. 64 kbit/s) and thus, the transmission of the binary data
via current methods of telephony is wasteful.
According to the teachings of the present invention, the
transmission efficiency of digital links is increased by
reproducing the originally scanned and encoded binary data from the
PCM signal of the modulated analog waveform and then transmitting
it along a transmission network as a 9.6 kbit/s signal. According
to an alternative embodiment of the invention the binary data is
transmitted as a 16 kbit/s signal which comprises the 9.6 kbit/s
signal and additional error correction code, thus significantly
increasing the robustness of the transmission in presence of line
errors. Without error correction, the system of the present
invention achieves a 6:1 compression ratio for facsimile
transmissions and with error correction it achieves a 4:1
compression ratio.
Reference is now made to FIG. 1, which is an overall functional
system block diagram of the transmission and reception end of a
telecommunication system, indicating three methods of signal
compression as well as the trunk expanding functions of the various
elements of the telecommunication system. The transmit side is
described with respect to FIG. 1. The receive side is mirror
symmetric and will not be described with respect to FIG. 1. Many of
the components of the telecommunication system are substantially
similar to those described and claimed in the aforesaid U.S. Pat.
No. 4,717,096, which is incorporated herein by reference, and
therefore, will not be described in detail. It will be appreciated
that the telecommunication system described in FIG. 1 can be
implemented in a point to point configuration, in a multiclique
configuration, and in a multidestination configuration, as defined
in CCITT Blue Book Rec. G.763. Additionally, it can be implemented
as an access terminal for traffic compression into a packet
switching network.
The transmission apparatus includes a trunk PCM interface (TDLI) 20
which is operative to provide interfacing between 1.544 Mbit/s or
2.048 Mbit/s PCM signals and the internal 2.048 Mbit/s (NRZ)
signals employed in the telecommunication system. It is operative
to provide synchronization plesiochronous buffering and optional
format conversion.
Downstream of TDLI 20 there is provided a time slot interchange
(TSI) 22 which provides time slot mapping. It enables up to ten
24-channel bit streams to be regrouped into eight 30/32 channel bit
streams.
Digital speech interpolation circuitry (DSI) 24 provides voice
compression by means of the time assignment speech interpolation
(TASI) of U.S. Pat. No. 4,523,309 and is operative to compress up
to 240 trunks generally into 62 bearer channels. Additionally, DSI
24 provides detection circuitry for classifying incoming signals as
selected facsimile signals, such as Group 3 facsimile signals, and
as other signals where other signals typically include speech, tone
and non-facsimile voiceband data. This enables the transmission
apparatus to separately compress facsimile signals and to apply the
conventional compression techniques for speech and non-facsimile
voiceband data signals.
Further compression is provide by a signal compression circuit 25
typically comprised of Adaptive Differential Pulse Code Modulation
(ADPCM) circuitry 26 and Variable Bit Rate (VBR) circuitry 28,
voiceband data optimized algorithm circuitry 27 and facsimile modem
29.
ADPCM circuitry 26 employs an ADPCM algorithm, in accordance with
the Red Book CCITT G.721 recommendation for compressing speech. VBR
circuitry 28 is typically provided in conjunction with ADPCM 26 and
is operative to effectively create additional bearer channels (in
excess of 62) to overcome periods of traffic overload, as described
in aforesaid U.S. Pat. No. 4,747,096. The ADPCM 26 and the VBR 28,
in conjunction with the DSI 24, provide a compression ratio of
typically 6:1 for speech signals. It will be appreciated that
circuitry employing other speech compression techniques, such as 16
kbit/s speech coding, can replace the ADPCM 26 circuitry.
Voiceband data is routed through voiceband data optimized algorithm
27 which employs ADPCM codecs specifically optimized for reliable
transmission of voiceband data, as described in aforesaid U.S. Pat.
No. 4,747,096. The voiceband data algorithm is transparent to
voiceband data signals and provides a 2:1 compression ratio. It
will be appreciated that the voiceband data compression may be
implemented using other algorithms, such as that of CCITT Blue
Book, Melbourne 1988, Rec. G.723.
In accordance with a preferred embodiment of the present invention,
facsimile modem 29 is provided for reproducing a plurality of
original facsimile binary data from a plurality of PCM signals, for
optionally incorporating error correction information into the
plurality of original facsimile binary data and for multiplexing
the resultant signals. The optional error correction function is
typically provided when the transmission network is of the type
where performance is typically degraded.
Multiplexer 31 multiplexes the output of the signal compression
stage, comprising ADPCM 26, VBR 28, voiceband data algorithm 27 and
facsimile modem 29 into one generally fully populated 2.048 or
1.544 Mbit/s signal. At each sample period, which is typically 125
microseconds, multiplexer 31 produces one bit frame with bits from
compressed channels.
An alternative embodiment of the invention comprises a multiplexer
31 which incorporates wideband packet technology, as described in
the aforementioned paper by R. W. Muise et al entitled "Experiments
in Wideband Packet Technology". In the alternative embodiment, the
multiplexer 31 is operative to act as a Packet Assembler (PA) to
gather and packetize a sequence of samples of compressed speech,
voiceband data or facsimile data and to subsequently transmit the
packets to a transmission network.
Interface between the 2.048 Mbit/s output from the multiplexer 31
to the standard 1.544/2.048 Mbit/s standard PCM bearer channels is
provided by the Bearer PCM Interface (TDLI) 30, described in
aforesaid U.S. Pat. No. 4,747,096.
Reference is now made to FIG. 2, which illustrates in block diagram
form certain elements of the transmission apparatus of the
telecommunication system pertaining to the present invention and
corresponding to the functional block diagram of FIG. 1. A complete
description of the remaining elements can be found in aforesaid
U.S. Pat. No. 4,747,096.
Eight 2.048 Mbit/s bit streams emerging from the TSI 22 are
supplied to the DSI circuitry 24 and are directed in parallel to a
transmit delay memory 50, to a facsimile detector 53 and to other
detectors, such as speech and tone detection circuitry 52.
Speech and tone detection (SPD) circuitry 52 typically comprises
four SPD circuits, each of which receives 2.times.2.048 Mbit/s
digital streams from the transmit TSI circuitry 22. The SPD
circuitry 52 is operative to examine each time slot for the present
of speech energy above an adjustable threshold which is normally
set at -32 dBmO.
If speech energy is present, a main CPU 44 is notified of the time
slot that has active speech. Additionally, the tone detector
portion of the SPD circuitry 52 examines the active speech for the
continuous presence of a 2100 Hz tone (CCITT Red Book Rec. G.164 or
Rec. V.25 for voiceband data or Rec. T.30 for facsimile data). When
the tone is detected, the main CPU 44 is notified.
Facsimile detector 53 additionally receives all eight of the 2.048
Mbit/s bit streams received from TSI 22 and detects the presence of
facsimile signals on them. Since Group 3 facsimile systems begin
their 300 bit/s transmissions with a preamble, defined in the 1984
CCITT Red Book Recommendation T.30 paragraph 5.3.1 to be a series
of flag characters transmitted for one second on a 300 bit/s
signal, it will be appreciated that the preamble is unique to
facsimile systems and thus, can be utilized for reliable detection
of facsimile signals; other data protocols transmit at most one or
two flag characters. Thus, facsimile detector 53 detects a
facsimile transmission upon identifying at least five consecutive
flag characters.
If a facsimile transmission is present, facsimile detector 53
notifies the main CPU 44 of the trunk channel in which it occurs.
If the detection occurs for a trunk channel which is not classified
as carrying facsimile signals, then the main CPU 44 marks the trunk
channel as a facsimile trunk channel. Until marked otherwise, the
trunk channel remains as a facsimile trunk channel and any further
detections of a facsimile transmission on that trunk channel are
ignored.
The main CPU 44, typically based on the Intel 80286 microcomputer,
controls the DSI operation as well as other functions of the
telecommunication system. Its major task, as part of the
transmission apparatus, is to receive activity information about
facsimile transmissions and other signals, such as speech, tone and
voiceband data, and to assign an available bearer bit portion to
the active trunk. In order to do so, it routes the time slots of
the eight 2.048 Mbit/s channels, via a transmit Digital Speech
Interpolation (DSI) switch 56, to either of the ADPCM 26, the
voiceband data algorithm 27 or the facsimile modem 29, depending on
the results of the SPD and tone detector 52 and the facsimile
detector 53. Main CPU 44 also indicates to a facsimile CPU 80 which
is part of the facsimile modem 29 and which is described in more
detail hereinbelow, in which time slot it will receive a facsimile
transmission and in which bit portion it should transmit the
demodulated facsimile transmission. The main CPU 44 additionally
detects the completion of a facsimile transmission on a facsimile
channel. The software for the main CPU 44 is taken mostly from
apparatus of the type described in the aforesaid U.S. Pat. No.
4,747,096.
Following initial detection of a facsimile transmission, the system
switches to a facsimile signal path. The switching takes place
during the first silent period during facsimile "handshake"
following detection. Effecting the switching during the silent
period avoids undesirable signal transients.
The transmit DSI switch 56 receives 8.times.2.048 Mbit/s digital
streams from the transmit delay 50 and selects, in response to
commands from the main CPU 44, an appropriate time slot. The
standard 2.048 Mbit/s bit stream contains 30 speech time slots
(TS); however, in accordance with U.S. Pat. No. 4,747,096, when TS
16 is not used for the transmission of signaling information, 31
time slots are available for speech.
Thus, two bit streams of up to 62 time slots during operation at
normal speech traffic levels, one bit stream with up to 31
voiceband data signals and one bit stream with up to 31 facsimile
signals are provided. Additionally, an additional 20 time slots are
provided for use during periods of traffic overload, as a result of
VBR operation. The 144 available time slots form an output of five
2.048 Mbit/s digital streams where the fifth 2.048 Mbit/s digital
strum comprises the 20 additional time slots. The remaining 11 time
slots of the fifth 2.048 Mbit/s digital stream are unused.
The first two and last one of the five 2.048 Mbit/s digital streams
are dedicated to trunk channels with speech activity, the third is
dedicated to trunks with non-facsimile voiceband data signals, and
the fourth is dedicated to trunks with facsimile transmissions.
DSI 24 also comprises a message generator 54 which receives 2 bytes
(16 bits) of message information from the main CPU 44. The message
information indicates to the receive circuitry the location, on the
bearer bit stream, of the assigned bits for each compressed trunk
channel and the type of traffic, speech, voiceband data or
facsimile data, carried therein.
Signal compression circuitry 25 comprises a signal compression
assembly 64 which receives the five 2.048 Mbit/s digital streams
from the transmitting DSI switch 56. The signal compression
assembly 64 comprises ADPCM encoders and data optimized ADPCM
encoders, fully described in aforesaid U.S. Pat. No. 4,747,096, and
facsimile demodulators 67 with optional Forward Error Correction
elements (FEC) 69, as described hereinbelow.
Each facsimile demodulator 67 demodulates the 64 kbit/s PCM bit
stream received from the DSI switch 56, thus reconstructing the
original scanned and encoded bit stream produced by the facsimile
machine 10. The optional FEC 69 adds error correction information
to the signal to increase the rate of the signal from up to 9.6
kbit/s to 16 kbit/s, a rate which is a submultiple of the 64 kbit/s
standard rate or the bearer bit stream.
Multiplexer 31 comprises a buffer memory 68 which combines the
outputs of the signal compression assembly 64 into one 2.048 Mbit/s
bearer signal. According to the traffic on the transmission
network, it will assign nibble time slots to compressed speech and
voiceband data signals and the appropriately sized time slots to
demodulated facsimile signals, as described hereinbelow.
According to an alternative embodiment of the present invention,
buffer memory 68 stores the output of the signal compression
assembly 64 and generates, typically every packet interval of 16
msec, packets of typically 128 4 bit samples with an additional 40
bits of packet header information. It should be noted that under
overload traffic conditions, the number of bits for each sample
will be smaller due to the operation of the VBR 28.
Buffer memory 68 releases the packets under control of the main CPU
44 which receives the speech, voiceband data and facsimile signal
activity information from SPD and tone detector 52 and facsimile
detector 53 every packet interval and assigns bearer bit portions
to each active trunk channel.
Reference is now made to FIG. 3 which illustrates the elements of
the facsimile demodulator 67 and or the optional FEC 69. According
to a preferred embodiment of the invention, facsimile demodulator
67 comprises a plurality of facsimile demodulators 126, such as the
R96MFX Monofax from Rockwell International, and a plurality of PCM
decoders 128 where each PCM decoder 128 is directly connected to a
facsimile demodulator 126. A typical transmission apparatus will
comprise 40 facsimile demodulators 126 and 40 PCM decoders 128. It
will be appreciated that the 40 facsimile demodulators 126 and 40
PCM decoders 128 are needed in order to decode and demodulate
facsimile signals from 31 incoming facsimile trunk channels due to
the initial overhead of the five demodulators 126.
At the beginning or each signal burst for a trunk channel marked as
carrying a 64 kbit/s facsimile transmission, one incoming time slot
is routed to typically five PCM decoders 128 via a facsimile
transmit TSI (TTSI) 124, such as the PEB 2040 PCM Switch from
Siemens. TTSI 124 typically selects the five PCM decoders 128 based
on which five facsimile demodulators 126 are currently
available.
According to a preferred embodiment of the invention, each PCM
decoder 128 converts the incoming PCM signal to the original analog
telephone waveform and sends the resultant signal to its
corresponding facsimile demodulator 126. It will be appreciated
that the PCM decoders 128 are included in order to utilize
inexpensive facsimile demodulators 126, such as the Rockwell
R96MFX, specifically designed for facsimile machines.
Each of the five facsimile demodulators 126 is tuned to one of the
five standard modes of operation for facsimile data, that is, 2.4
or 4.8 kbit/s modulated according Rec. V.27 ter, 7.2 or 9.6 kbit/s
modulated according to Rec. V.29 or 300 bit/s, modulated according
to Rec. V.21. Each demodulates the analog telephone waveform it
receives from its PCM decoder 128 in an attempt to identify the
mode of operation by which the present portion of the facsimile
transmission is modulated.
It will be appreciated that it is possible to analyze the facsimile
transmission with one facsimile demodulator 126 by utilizing the
facsimile demodulator 126 specifically designed for use in
facsimile machines 10 to interpret the 300 bit/s protocol between
pages which indicate which mode of operation will be used for
scanning and encoding the following page. This method has one
drawback in that CCITT Red Book Rec. T.30 allows for non-standard
protocols between facsimile machines 10.
Thus, a facsimile demodulation system which utilizes one standard
facsimile demodulator 126 per facsimile transmission might be
unable to interpret the non-standard protocols and thus, be unable
to demodulate facsimile transmissions. Therefore, according to a
preferred embodiment of the present invention, five facsimile
demodulators 126 are utilized to identify the mode of operation of
every portion of a facsimile transmission whether it be the 300
bit/s standard or non-standard dialog or the up to 9.6 kbit/s page
transmission.
The demodulated data are sent to a buffer 130 and stored there
until the demodulator tuned to the correct bit rate and mode of
operation is identified. The identification typically takes 0.3
seconds to achieve a positive identification of either a V.29 or
V.21 modem by a given demodulator, after which the remaining four
demodulators 126 are available and the data they produced in buffer
130 is ignored. Should no positive identification of either the
V.29 or V.21 modems is made during the 0.3 second interval and if
during this interval an 1800 Hz tone is detected, then the two
demodulators which are tuned to the two alternative transmission
rates of the V.27 modem continue to operate. Once positive
identification is made by either of those two demodulators, the
demodulator which did not make a positive identification becomes
available and its output in the buffer 130 is ignored.
The identifying demodulator 126 continues demodulating the signal
and sending it to the buffer 130 until the signal terminates,
typically at the end of the transmission of one page or at the end
of a 300 bit/s message transmission.
It is a particular feature of the present invention that
notwithstanding the different times needed to detect the various
modems and notwithstanding that detection of the V.27 modem
requires more than 0.3 seconds, a 0.3 second delay is sufficient to
avoid loss of the beginning of the transmitted signal. This is
achieved by commencing transmission of the training sequence
characteristic of the V.27 modem once identification of the 1800 Hz
signal is made but before positive identification of which
transmission mode (i.e. 4.8 or 2.4 kbit/s) has been made.
The buffer 130 is operative to receive the data from the facsimile
demodulators 126 as 8 bit words and to organize it such that, on
average, a 9.6 kbit/s bit stream is sent. If the demodulated
information is at a rate less than the maximal 9.6 kbit/s, then the
data rate is increased to 9.6 kbit/s by dummy bit insertion.
The buffer 130 achieves the 9.6 kbit/s average bit stream by
ensuring that generally 48 bits are sent within milliseconds. The
48 bits are organized such that at every millisecond, either 10
bits or 9 bits are transmitted. Thus, in each millisecond, three
channels of facsimile data are multiplexed into 32 bits,
transmitted in 8 sampling frames as 4 bit nibbles per frame.
It should be noted that the remaining 2 to 5 bits of the 32 bits in
each millisecond, depending on the number of bits sent per each
facsimile channel, are dummy bits. This method achieves a 6:1
compression ratio, i.e. transmission of 6 trunks of 64 kbit/s PCM
signals via a single 64 kbit/s time slot in the bearer bit
stream.
A selector 136 selects, under control of a facsimile transmit CPU
(TCPU) 134, the correctly demodulated and multiplexed signals
stored in buffer 130 sends them to multiplexer 31 as one partly
populated 2.048 Mbit/s digital bit stream.
According to an alternative embodiment of the invention, the signal
from the selector 136 is routed through FEC 69 which adds forward
error correction to the 9.6 kbit/s signal, typically using the
Hamming (15,11) code. Thus, to the 10 or 9 bits, described
hereinabove, are added 1 or 2 dummy bits, respectively, where one
of the bits serves as a message bit to indicate the number of
original bits, to produce 11 bits, another 4 of error correction
based on the Hamming (15,11) code, and a final dummy bit to
increase the bit count to 16. Thus, two channels of facsimile data
are multiplexed into a 32 kbit/s channel, producing a 4:1
compression ratio, i.e. transmission of 4 trunks of 64 kbit/s PCM
signals via a single 64 kbit/s time slot in the bearer bit
stream.
The operation of the facsimile demodulator 67 is controlled by
facsimile CPU 134 which polls the status of the demodulators 126
via a status and control read/write 132, selects five demodulators
126 upon reception of a signal burst, tunes each one to a different
standard mode of operation, and indicates to TTSI 124 to switch the
current time slot to the five PCM decoders 128. Additionally, it
identifies the demodulator 126 which is tuned to the correct mode
of operation and indicates to the selector 136 to transmit the data
from the identified demodulator 126 to the buffer memory 68, or
alternatively, to FEC 69 and from there to buffer memory 68.
The facsimile CPU 134 additionally is connected to the main CPU 44
which indicates to the facsimile CPU 134 which time slots have
facsimile data in them, when the facsimile signal burst commences
or terminates, and when the facsimile transmission is complete. The
completion of a facsimile transmission on a facsimile channel is
defined according to the following criteria:
1. A silence period lasting for at least 10 seconds is detected by
SPD and tone detector 52 (FIG. 2A); or
2. The five facsimile demodulators 126 attempting to demodulate the
facsimile transmission fail to do so within a predetermined length
of time, typically 500 ms.
If condition 1 is true, then main CPU 44 causes any following
signal bursts on that trunk channel to be switched to an ADPCM
encoder for speech. If condition 2 is true, the trunk channel is
switched to a data optimized ADPCM encoder.
Reference is now made to FIG. 4, which illustrates in clock diagram
form certain elements of the reception end of a telecommunication
system pertaining to the present invention. The reception end
corresponds to the mirror of the functional block diagram of FIG. 1
and the signal progresses from a BDLI, to a signal decompression
unit, to DSI circuitry and finally, to a TDLI, as described in
aforesaid U.S. Pat. No. 4,747,096.
The receive circuitry of FIG. 4 comprises a message receiver 94
(FIG. 3B) which looks for an exclusive message identification code
and the message contents following it. Once detected, the message
contents are transferred to the main CPU 44 which decodes it to
discover the location, on the bearer bit stream, of the assigned
bits for each compressed trunk channel and the type of traffic,
speech, voiceband data or facsimile data, carried therein. As noted
in U.S. Pat. No. 4,747,096, the main CPU 44 controls both the
transmit and receive functions of the system and, in receive mode,
controls DSI switch 95 in accordance with the assignment messages
received.
The generally fully populated 2.048 Mbit/s delayed output of
receive delay 90 is supplied to a buffer memory 96 which forms part
of signal decoding circuitry 98. The buffer memory 96 outputs to a
plurality of decoders 100, each comprising voice ADPCM decoders
101, data optimized ADPCM decoders 103, and facsimile encoders 105
with optional Error Correction (EC) 107, and is controlled by the
main CPU 44 through control memory 97.
The received compressed signals are routed to the appropriate
decoder type 101, 103 or 105, along 2.048 Mbit/s digital bit
streams, in accordance with the messages received. Each set of
voice ADPCM decoders 101 and each set of data optimized ADPCM
decoders 103 can potentially produce two 2.048 Mbit/s digital bit
streams of 8-bit PCM samples upon decoding one fully populated
2.048 Mbit/s digital bit stream of compressed signals. Each set of
facsimile encoders 105 can potentially produce one 2.048 Mbit/s
digital bit stream of 8-bit PCM per sample channels upon encoding
one partly populated 2.048 Mbit/s digital bit stream of 9.6 Kbit s
demodulated facsimile signals, 6:1 decompression is provided when
Error Correction EC 107 is not implemented and 4:1 decompression is
provided when EC 107 is employed.
According to an alternative embodiment of the invention, buffer
memory 96 receives packets of samples of either compressed speech,
non-facsimile data or facsimile data. Buffer memory 96 is operative
to store the received packets and to individually release the
samples to the appropriate one of the plurality of decoders
100.
The receive DSI 95 switch receives the 2.048 Mbit/s digital streams
of 8-bit PCM samples from the signal decoders 100. They are
switched to eight 2.048 Mbit/s bit streams under control of CPU 44,
in accordance with the routing message received from the far end
terminal.
Reference is now made to FIG. 5 which illustrates the elements of
the facsimile encoder 105 and of the optional EC 107. According to
an alternate embodiment of the invention, the EC 107 performs error
correction on the 16 kbit/s demodulated signal with error
correction information received from buffer memory 96. The EC 107
first strips the signal of the dummy sixteenth bit. Using the
Hamming (15,11) code, the EC 107 corrects any errors produced by
the transmission and produces an 11 bit corrected signal. In order
to produce the original 10 or 9 bit signal, one or two dummy bits,
respectively, are subsequently stripped off, according to the
status of the message dummy bit. The original 9 or 10 bit signal is
sent to a buffer 140.
According to a preferred embodiment of the invention, facsimile
decoder 105 comprises a plurality of facsimile modulators 142, such
as the R96MFX Monofax from Rockwell International, and a plurality
of PCM coders 144, where each PCM coder 144, is directly connected
to a facsimile modulator 142. A typical facsimile decoder 105
comprises 31 facsimile modulators 142 and 31 PCM coders 144.
The facsimile decoder 105 operates as follows. The 9.6 kbit/s
signal is received by butter 140 as sequences of 9 or 10 bits.
Buffer 140 stores the bits as they arrive and rebuilds the signal
as an 8 bit signal which it then sends to a facsimile modulator 142
which has been tuned, by a facsimile Receive CPU (RCPU) 146, to the
mode of operation by which the signal was demodulated on the
transmit side. If the received facsimile data was originally
scanned and encoded at a rate lower than 9.6 kbit/s, then the
additional dummy bits are stripped in the buffer 140 and the 8 bit
signal is sent to a facsimile modulator at a respectively lower
rate.
The analog telephone waveform resulting from the facsimile
modulator 142 is then sent to the corresponding PCM coder 144 which
encodes the analog signal as a PCM signal. The plurality of PCM
signals produced by the PCM decoders 144 are routed to the
appropriate time slot in the trunk bit stream by a facsimile
Receive TSI (RTSI) 148, such as the PEB 2040 PCM Switch from
Siemens.
According to a preferred embodiment of the invention, facsimile
RCPU 146 is operative to indicate to the buffer 140 how to rebuild
the 8 bit signal and to which facsimile modulator 142 to send the
rebuilt signal. It also tunes the selected facsimile modulator 142
to the correct mode of operation according to directions received
from the main CPU 44. Finally, it indicates to the facsimile RTSI
148 the time slots on the trunk bit stream corresponding to the
outputs of the plurality of PCM coders 144.
It will be appreciated that a facsimile compression system such as
described hereinabove can be constructed outside of an
telecommunication system using elements functionally similar to
those described hereinabove. However, incorporating such a system
within an existing system, such as a digital circuit multiplication
system or a speech packetization system, reduces the number of new
elements which must be built since many of the necessary elements
are already incorporated into the existing system.
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