ITU-T has introduced the following recommendations for facsimil e communication.
•
V.8 (1994): Procedures for starting sessions.
•
V .34 (1994): Specifications for modulati on and prot ocol f or modems operat ing at
up to 28,800 bps (modified in 1996 to allow data rates of up to 33,600 bps)
V.34 introduces a lot more technical c hanges com pared with the previ ous speed
upgrade from V.29 to V.17.
Signals used in V.34 procedures include t one signals, and data signals at 300
bps, 600 bps, 1200 bps, and from 2.4 kbps to 33.6 kbps.
•
T. 30 (1996): This recommendati on has been modif i ed to include changes to
protocol signaling as a result of V.8 procedure implementati on.
1.2 PRINCIPAL CHARACTERISTICS
The principal characteristics of V.34 procedure are as follows:
1. The use of Error Correction Mode (ECM) is mandatory.
2. Facsimile machines with a V.34 modem must support V.8.
3. Once V.34 is selected for communication bet ween two termi nals , V.17, V.29,
V.27ter are not applied.
In addition, for best results, good line condi tion is required.
Bandwidth
For 26.4 kbps, a bandwidth of 3000 Hz is required.
For 28.8 kbps, a bandwidth of 3200 Hz is required.
For 33.6 kbps, a bandwidth of 3429 Hz is required.
Noise Level
For 28.8 kbps, the signal-to-noise (S/N) ratio must be 32-34 dB or better.
1-1
PHASES OF THE V.34 PROCEDURE18 March 1998
1.3 PHASES OF THE V.34 PROCED URE
The protocol procedure for a V.34 fax communication consists of 6 phases. The
following explain the phases briefly.
1.3.1 BASIC PHASES
Phase 1: V.8 Sequence
The calling and called terminals exchange available modulation m odes (fax or data
modem) and data transmission direction informati on, and decide a communication
mode.
Phase 2: Line Probing
The receiving terminal determines the available bandwidth for t he fax data
transmission channel (known as the primary channel ) based on the analysis of line
probing signals sent from the transmitting termi nal. This bandwidth is informed to
the transmitting side as a symbol rate.
Phase 3: Primary Channel Equalizer Training
The receiving terminal adjusts its equal i zer etc., while receiving training signals
from the sender. The tx side uses the data transmission modulat ion parameters
informed by the rx side at the end of phase 2.
Phase 4: Control Channel Start-up
Both terminals determine a data rate for t he primary channel (i n other words, for
data transmission).
Phase 5: C ontrol Channel
Both terminals exchange T.30 protocol si gnals (DIS/DCS, NSF/NSS) to determine
transmission parameters (this equivalent to phases B and C of T.30 protocol)
Phase 6: Primary Channel
The sending terminal sends fax image data at the data rate that was determined
with the receiver in phase 4. One ECM block is sent at a time.
Post Messag e Pro ce dure
After the primary channel has finis hed, bot h terminal s restart the control channel to
exchange post message signals, as former fax machi nes do in phase E of T.30
protocol.
If there is another ECM block to send, the machines then start th e primary channel
again, otherwise they disconnect the line.
1-2
18 March 1998PHASES OF THE V.34 PROCEDURE
1.3.2 PROTOCOL OVERVIEW
V.8/V.34 Protocol Sequence (1 page/ 1 block)
Dial
Phase 1
(V.8 Procedure)
75 ms
Phase 2
(Line Probing)
70 ms70 ms70 ms
Phase 3
Training)
(Primary Ch. EQ.
Phase 4
(Control Ch. Start-up)
Phase 5
(Control Channel)
1200 bps
or
CNG
CM
CJ
INFO0c
B
B bar
L1
L2
B
S
S bar
PP
TRN
PPh
ALT
MPh
MPh
E
Flag
DCS
Flag
1's
1100 Hz
300 bps
300 bps
600 bps
1200 Hz
1200 Hz
Spectrum
Spectrum
1200 Hz
1200 bps
1200 bps
1200 bps
NSSTSI
TXRX
ANSam
2100 Hz
JM
300 bps
600 bps
INFO0a
2400 Hz
A
A bar
2400 Hz
A
2400 Hz
600 bps
INFOh
(Symbol Rate, etc.)
PPh
1200 bps
ALT
1200 bps
MPh
(Data Rate, etc.)
MPh
E
1200 bps
NSF
CSI
1200 bps
DIS
Flag
CFR
Flag
(Silence)
75 ms
TXRX
S
S bar
PP
B1
(Pix Data)
70 ms
Symbol Rate
Data Rate
Primary
Channel
Turn-off
Sh
Sh barSh
1200 bps
1200 bps
DisconnectDisconnect
(baud)
(kbps)
Higher Frequency
ALT
E
PPS-
EOP
Flag
DCN
1's
24002800300032003429
26.4
24.0
21.6
21.6
19.2
19.2
16.8
16.8
14.4
14.4
12.0
12.0
9.69.69.69.69.6
7.27.27.27.27.2
4.84.84.84.84.8
2.4
Sh bar
1200 bps
ALT
E
1200 bps
Flag
MCF
Flag
(Silence)
31.231.2
28.828.828.8
26.4
26.4
24.0
24.0
21.6
21.6
19.2
19.2
16.8
16.8
14.4
14.4
12.0
12.0
You hear higher frequency signals in
phases indicated with light gray.
33.6
26.4
24.0
21.6
19.2
16.8
14.4
12.0
Phase 6
(Primary Channel)
Phase 4
(Control Ch. Restart)
Phase 5
Post Message
(Control Channel)
1-3
Lower Frequency
You hear lower frequency signals in
phases indicated with dark gray.
SINGLE_PAGE_TX.WMF
18 March 1998PHASE 1: V.8 SEQUENCE
2. BASIC PROCEDURE
2.1 PHASE 1: V.8 SEQUENCE
2.1.1 OVERVIEW
CallingCalled
1100 Hz
300 bps
(V.21L)
300 bps
(V.21L)
CNG
CM
CJ
Full Duplex
ANSam
JM
2100 Hz
300 bps
(V.21H)
Ph_1.WMF
V.8 protocol establishes communication between the calling modem and the
answering modem. The general communication functions and modulation modes
are exchanged. The best modulation mode for the calling and answering modems
is determined upon the exchange of call menu (CM) and joint menu (J M) signals.
Transmitted from the calling terminal to indicate the start of a
communication.
Transmitted from the calling terminal primarily to indicate its
available modulation modes.
Transmitted from the receiving terminal primarily to indicate the
modulation modes available in both terminals.
Acknowledges the detection of a JM signal and indicates the
end of the CM signal.
The V.8 sequence starts from the ANSam signal from the called terminal. The
ANSam signal is a 2100 Hz tone signal that is amplitude modified with a 15Hzcosine wave. Also, the signal phase of ANSam inverts every 450 ms. The ANSam
signal has the same frequency as CED, and non-V.8 machines cannot tell the
difference.
The calling and called terminals exchange information about availabl e V-s eri es
modulation modes and the direction of the communic ati on, usi ng CM and JM
signals. As CM/CJ from the calling terminal and JM from the called terminal use
different modulation modes, V.21L and V.21H, both terminals can communicate in
full-duplex mode.
2-1
PHASE 1: V.8 SEQUENCE18 March 1998
If a communication mode (e.g., V.34 fax communication to calling terminal to called
terminal) is available at bot h term i nals, the t e rminals communi cate using that
communication mode for the subsequent phases. Otherwise, both terminals
disconnect the line.
Communication also ends if the calling side requests polling, but t here is no data
on polling standby at the called side.
2.1.3 PROCEDURE
Calling TerminalCalled Terminal
After dialing, the machine sends CNG
signal and waits for an ANSam signal.
After ANSam detection, the machine sends
CM, while waiting for a JM.
CM settings:
• Normal transmission: 81 85 D4
• Polling reception: A1 85 D4
After JM detection, the machine sends CJ.
After ring detection, the called terminal
sends ANSam signal for up to 3.2 s, while
waiting for a CM signal from the calling
terminal. (See the note after the table.)
After CM detection, the machine sends
JM, while waiting for a CJ.
JM Settings
• Normal reception: 81 85 D4
• Polling transmission: A1 85 D4
Both terminals go into phase 2 (line probing) 75 ms after CJ .
If no communication mode is commonly availabl e at bot h sides (for exam ple, if a
fax modem has called a data modem), both terminals disc onnect the line after the
JM and CJ signals.
Refer to section 3.1 for various V.8 sequences.
NOTE:
The ITU-T recommendation for the ANSam length is 2.6 to 4.0 s. Ricoh
uses 3.2 s (as of February, 1998).
If no response to an ANSam signal is detected within the maximum
signal duration, it is assumed that V. 8 protoc ol is not supported, and
communication takes place in accordance with recommendation T.30.
2.1.4 ERROR CODES
0-70: Refer to section 4.1. 1.
•
0-74: Refer to section 4.1. 2.
•
0-75: Refer to section 4.1. 3.
•
0-76: Refer to section 4.1. 4.
•
0-77: Refer to section 4.1. 5.
•
2-2
18 March 1998PHASE 2: LINE PROBING
2.2 PHASE 2: LINE PROBING
2.2.1 OVERVIEW
TXRX
600 bps
1200 Hz
1200 Hz
Spectrum
Spectrum
1200 Hz
INFO0c
B
B bar
L1
L2
B
INFO0a
A
A bar
A
INFOh
(Symbol Rate, etc.)
600 bps
2400 Hz
2400 Hz
2400 Hz
600 bps
Ph_2.WMF
Phase 2 establishes the condition of the line, which decides the bandwidth
available for the communication.
2.2.2 SIGNALS
INFO0cA signal transmitted from the calling terminal to indicate its available
modem capabilities and data mode modulation parameters.
INFO0a
BA modem control signal of 1200 Hz.
B barThe same as B, but with phase inverted.
AA modem control signal of 2400 Hz.
A barThe same as A, but with phase inverted.
L1
L2A line probing signal to analyze line characteristics. This signal is
INFOhA signal used by the receiving terminal to inform the results of line
A signal transmitted from the receiving terminal to indicate its
available modem capabilities and data mode modulation parameters.
A line probing signal to analyze line characteristics. L1 is 6 dB higher
than L2. This signal is used to check the amplitude distortion.
used to check the amplitude distortion.
probing. The symbol rate is informed by this signal.
2-3
PHASE 2: LINE PROBING18 March 1998
The aim of phase 2 is to determine a set of modulation parameters that will be
used in phase 6 (the primary channel) for image data transmission.
Both modems exchange information about their capabilities and m odulation
parameters using INFO0c and INFO0a signals. Then the transmitting terminal
sends L1 and L2, which are known as probing tones. These tones allow the
receiving modem to analyze the network qualities, such as bandwidth and noise
level.
Based on its analysis of how well the network passed the probing tones, the
receiving modem informs a set of modulati on param eters, such as symbol rate,
pre-emphasis, and power reduction, using the INFOh signal.
Symbol rateThe symbol rate is a baud rate. However, the data can be
modulated in different ways using this symbol rate, to achieve
different data rates. If line condition is good, a higher data rate
can be selected. The data rate is selected in phase 4.
Pre-emphasis
Power reduction
A linear equalization method where the transmitted signal
spectrum is shaped to compensate for attenuation distortion.
When the receiving modem’s power level is detected to be
high, the transmitting Tx level is reduced by up to 7 dB.
Both modems then go into phase 3 (equalizer training) 70 ms after I NFOh.
2.2.3 PROCEDURE
Sender TerminalReceiver Terminal
75 ms after the end of phase 1, the
machine sends INFO0c.
When the machine detects an INFO0a, it
stops INFO0c and sends B and B bar
tones.
When the machine detects A bar, it sends
line-probing signals (L1 and L2).
After L2 has finished, the machine sends B
tone again.
When the machine receives an INFOh
signal, it stops B.
Both terminals go into phase 3 (control channel start-up) 70 ms after above steps.
75 ms after the end of phase 1, the
machine sends INFO0a.
When the machine detects an INFO0c, it
stops INFO0a and sends A and A bar
tones.
When the machine detects B bar, it starts
waiting for line-probing signals (L1 and
L2).
After L2 reception has finished, the
machine sends A tone again followed by
INFOh signal
2.2.4 ERROR CODES
•
0-80: Refer to section 4.2. 1.
2-4
18 March 1998PHASE 2: LINE PROBING
2.2.5 PROBING TONES
The table shows the range of frequencies that the tx side sends to the rx side in the
L1 and L2 signals. As can be seen, the phase sometimes reverses.
The above table shows the required bandwidths for V.27, V.29, V.17, and V.34.
Bandwidth is one of the important factors the modems use to select a symbol rate.
As shown in the table, the faster the modulation, the wider t he requi red bandwidth .
This is because required bandwidth for a modulation depends on symbol rate and
carrier frequencies.
Other factors determining the symbol rate are signal to noise levels.
2-5
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