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The unit uses MODEM (IC111) that serves as an interface between the control section for FAX transmission and reception and
the telephone line. During a transmitting operation, the digital image signals are modulated and sent to the telephone line.
During a receiving operation, the analog image signals which are received via the telephone line are demodulated and con-
verted into digital image signals. The communication format and procedures for FAX communication are standardized by ITU-T.
MODEM has hardware which sends and detects all of the necessary signals for FAX communication. 
It can be controlled by writing commands from the ASIC (IC106: inside ASIC).
This MODEM also sends DTMF signals, generates a call tone (from the speaker), and detects a busy tone and dial tones.

Overview of Facsimile Communication Procedures (ITU-T Recommendation):

1. ON CCITT (International Telegraph and Telephone Consultative Committee) 

The No. XIV Group of ITU-T, one of the four permanent organizations of the International Telecommunications Union (ITU),
investigates and make recommendations on international standards for facsimiles.

2. Definition of Each Group

• Group I (G1) 

Official A-4 size documents without using formats which reduce the band width of a signal are sent over telephone lines.
Determined in 1968. 
Transmission for about 6 minutes at a scanning line density of 3.85 lines/mm.

• Group II (G2) 

Using reduction technology in the modulation/demodulation format, an A-4 size document is sent at an official scanning line
density of 3.85 lines/mm for about 3 minutes. 
Methods to suppress redundancy are not used.
Determined in 1976.

• Group III (G3) 

Method of suppressing redundancy in the image signal prior to modulation is used. An A-4 size document is sent within 
about one minute.
Determined in 1980.

• Group IV (G4) 

Transmission is via the data network. A method is provided for suppressing redundancy in signals prior to transmission, and 
error-free reception of transmission is possible.
The scope of these facsimile applications is not limited simply to transmission of written statements. Through symbiotic link-
ages with other communication methods, it can be expected to expand to include integrated services.

3. Facsimile Call Time Series

As shown in the following diagram, the facsimile call time series is divided into five phases.

Phase A: Call setting 
Call setting can be manual/automatic. 
Phase B: Pre-message procedure 
Phase B is a pre-processing procedure and sequence for confirming the status of the terminal, transmission route, etc., and
for terminal control. It implements terminal preparation status, determines and displays terminal constants, confirms synchro-
nization status, etc. and prepares for transmission of facsimile messages. 
Phase C: Message transmission 
Phase C is the procedure for the transmitting facsimile messages.
Phase D: Post message procedure 
Phase D is the procedure for confirming that the message is completed and received. For continuous transmission, phase B
or phase C is repeated for transmission. 
Phase E: Call retrieval 
Phase E is the procedure for call retrieval, that is for circuit disconnection.

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4. Concerning Transmission Time

Transmission Time   =    Control Time  +    Image Transmission Time     +    Hold Time

Transmission time consists of the following.
Control time:

This is time at the start of transmission when the functions at the sending and receiving sides are confirmed, the 

trans-

mission mode is established, and transmission and reception are synchronized.

This is the time required for the transmission of document contents (image data). In general, this time is recorded  in  the
catalog, etc.

This is the time required after the document contents have been sent to confirm that the document was actually sent, and
to check for telephone reservations and/or the existence of continuous transmission.

5. Facsimile Standards

6. Explanation of Communication and Compression Technology

a. G3 Communication Signals (T. 30 Binary Process) 

For G3 Facsimile communication, this is the procedure for exchanging control signals between the sending and receiving

 

Item

Telephone Network Facsimile

G3 Machine

Connection Control Mode

Telephone Network Signal Mode

Terminal Control Mode

T. 30 Binary

Facsimile Signal Format

Digital

Modulation Mode

PSK (V. 27 ter) or QAM (V. 29)

Transmission Speed

300 bps (Control Signal)
 
2400, 4800, 7200, 9600, 12000, 14400 bps (FAX Signal)

Redundancy Compression
 
Process
 
(Coding Mode)

1 dimension: MH Mode
 
2 dimension: MR Mode (K=2.4)

Resolution

Main Scan: 8 pel/mm
 
Sub Scan: 3.85, 7.7l/mm

Line Synchronization Signal

EOL Signal

1 Line Transmission Time
 
[ms/line]

Depends on the degree of data reduction.
 
Minimum Value: 10, 20
 
Can be recognized in 40ms.

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machines both before and after transmission of image signals.
Control signals at 300 bps FSK are: 1850 Hz...0, 1650Hz...1. 
An example of a binary process in G3 communication is shown below.

Explanation of Signals 
Control signals are comprised mainly of 8-bit identification signals and the data signals added to them. Data signals are
added to DIS and DCS signals.
Signal.....DIS (Digital Identification Signal) 
Identification Signal Format.....00000001
Function:
Notifies the capacity of the receiving unit. The added data signals are as follows.

Signal.....DCS (Digital Command Signal) 
Identification Signal Format.....X1000001

Example
 (Some models do not support the following items.):

Bit No.

DIS/DTC

DCS

1

Transmitter --- T.2 operation

2

Receiver --- T.2 operation

Receiver --- T.2 operation

3

T.2 IOC = 176

T.2 IOC = 176

4

Transmitter --- T.3 operation

5

Receiver --- T.3 operation

Receiver --- T.3 operation

6

Reserved for future T.3 operation features

7

Reserved for future T.3 operation features.

8

Reserved for future T.3 operation features.

9

Transmitter --- T.4 operation

10

Receiver --- T.4 operation

Receiver --- T.4 operation

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11,12,13,14
 
0,0,0,0
 
0,1,0,0
 
1,0,0,0
 
1,1,0,0
 
0,0,1,0
 
0,1,1,0
 
1,0,1,0
 
1,1,1,0
 
0,0,0,1
 
0,1,0,1
 
1,0,0,1
 
1,1,0,1
 
0,0,1,1
 
0,1,1,1
 
1,0,1,1
 
1,1,1,1

Data signaling rate
 
V.27 ter fall back mode
 
V.27 ter 
 
V.29
 
V.27 ter and V.29
 
Not used
 
Reserved
 
Not used
 
V.27 ter and V.29 and V.33
 
Not used
 
Reserved
 
Not used
 
V.27 ter and V.29 and V.33 and V.17
 
Not used
 
Reserved
 
Not used
 
Reserved

Data signaling rate
 
2400 bit/s, V.27 ter
 
4800 bit/s, V.27 ter
 
9600 bit/s, V.29
 
7200 bit/s, V.29
 
14400 bit/s, V.33
 
12000 bit/s, V.33
 
Reserved
 
Reserved
 
14400 bit/s, V.17
 
12000 bit/s, V.17
 
9600 bit/s, V.17
 
7200 bit/s, V.17
 
Reserved
 
Reserved
 
Reserved
 
Reserved

15

R8

×7.7 lines/mm and/or 200×200 pels/25.4mm

R8

×7.7 lines/mm and/or 200×200 pels/25.4mm

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Two-dimensional coding capability

Two-dimensional coding capability

17, 18
 
(0, 0)
 

 
(0, 1)
 

 

 

 

 

 
(1, 0)
 

 

 

 
(1, 1)

Recording width capabilities
 
1728 picture elements along scan line length of 
 
    215 mm ± 1%
 
1728 picture elements along scan line length of 
 
    215 mm ± 1%
 
2048 picture elements along scan line length of 
 
    255 mm ± 1%
 
2432 picture elements along scan line length of 
 
    303 mm ± 1%
 
1728 picture elements along scan line length of 
 
    215 mm ± 1%
 
2048 picture elements along scan line length of 
 
    255 mm ± 1%
 
Invalid

Recording width
 
1728 picture elements along scan line length of 
 
    215 mm ± 1%
 
2432 picture elements along scan line length of 
 
    303 mm ± 1%
 

 

 

 

 
2048 picture elements along scan line length of 
 
    255 mm ± 1%
 

 

 
Invalid

19, 20
 
(0, 0)
 
(0, 1)
 
(1, 0)
 
(1, 1)

Maximum recording length capability
 
A4 (297 mm)
 
Unlimited
 
A4 (297 mm) and B4 (364 mm)
 
Invalid

Maximum recording length
 
A4 (297 mm)
 
Unlimited
 
B4 (364 mm)
 
Invalid

Bit No.

DIS/DTC

DCS