Troubleshooting Of Super G3 Fax - Xerox WorkCentre Pro 423 Service Manual

2.3.3.5 Troubleshooting of Super G3 Fax

Super G3 fax uses analogue communication and its troubleshooting is basically the same as
that of the conventional G3 Fax. However, since the communication speed and procedure are
different, this section describes troubleshooting unique to Super G3 mode.
Super G3 Fax realizes communication up to 28,800 bps by a modem of the V.34 standard.
The speed can be optionally increased up to 33,600 bps.
The conventional speed is 14,400 bps (V.17). To realize the high-speed communication of
V.34, the conventional data transmission rate must be more than doubled. Therefore, the
telephone line quality will affect communication more than ever.
available for error-free communication at 14,400 or 9600 bps may cause an error in Super G3
communication.
An ordinary analogue public line shows a good frequency characteristic in a band from 300 to
3,400 Hz. In Super G3 communication, the communication speed may differ if only the
direction of communication is reversed without changing the parties or the telephone line. In
this communication, the transmission side determines the communication speed according to
the result of line quality measurement by the probing function in the V.34 procedure and the
probing result varies each time the direction of communication is reversed. In other words,
Super G3 mode cannot always achieve the maximum speed (33,600 bps). In most cases, the
Super G3 communication speed is 21,600 bps or more.
The conventional fax up to 14,400 bps uses half-duplex communication where signals are
sent alternately. Super G3 fax, however, uses full-duplex communication of a different
communication procedure. In full-duplex communication, both faxes issue signals together.
While sending signals, each fax monitors signals from the other fax. The communication
status can be supervised by monitoring a line for sounds in the conventional fax
communication but not in Super G3 communication. If a communication error occurs, the
analysis of protocol monitor data is necessary more than ever and the trace data of both the
transmitter and receiver may be compared often.
Notes on Super G3 troubleshooting
ECM: ECM is essential for Super G3 communication. If the ECM function is OFF, even a fax
supporting Super G3 mode will use not V.34 but V.17/V.29 (14,000/9600 bps) for
communication.
Communication procedure: The Super G3 communication procedure consists of V.8 and
V.34. The V.8 procedure is used to check the Super G3 mode capability and to determine the
communication speed. Once the V.8 procedure has terminated normally, Super G3 fax
changes to the V.34 procedure and sends image information by the V.34 procedure. The V.34
procedure uses the same commands as the G3 procedure (V.17/V.29 or other) and the
protocol trace data is also almost the same. However, the actual communication type is full
duplex and the command transmission speed is 1200 bps.
The V.8 procedure uses the tonal signals of CNG or CI sent from an originating terminal for
manual transmission and ANSam sent from a terminating terminal. If the line receives noises
or the signal level is low, an error occurs because the remote terminal cannot recognize the
tonal signals correctly. For this check, protocol data of the remote terminal is checked to see
whether signals sent from the local terminal are recorded (as recorded in the local trace data).
WorkCentre Pro 423/428
The V.34 procedure is executed in the order of phases 2, 3, and 4 and [V34ph2], [V34ph3],
and [V34ph4] are recorded in the protocol trace data. Once phase 4 has terminated normally,
the procedure changes to phases B, C, D, and E. For troubleshooting in these phases,
reference the conventional procedure.
If the line receives noises or the signal level is low, the procedure may not progress smoothly.
If phases 2, 3, and 4 are repeated, [V34ph2], [V34ph3], and [V34ph4] are recorded again and
again in the protocol trace data. If an error occurs in phase 2, [V34ph2] is recorded but
[V34ph3] and [V34ph4] are not.
In both of the above two cases, the analog characteristics of the telephone line are defective
or the send level is inappropriate.
Even a telephone line
Send level:
important. Especially, the signal to noise level (S/N) ratio is the key. For correct signal
detection, a certain S/N ratio is necessary. The protocol data may indicate that the remote
terminal sends the same signal repeatedly or does not advance to the next procedure. This
means that the remote terminal cannot recognize signals from the local terminal. In this case,
change the send level. If the noise level does not change, raising the send level should
increase the S/N ratio. When changing the send level, vary the send level a little (1 or 2 dB)
and find the best value by trying communication several times.
If a digital line (ISDN/corporate digital leased line) or digital equipment (digital PBX/TA) is in
use, raising the level too high will cause a waveform disorder to an analog signal and disable
normal communication (high-level signal waveforms are deformed at analog-digital
conversion). Under this kind of line environment, lowering the send level will establish good
communication.
Speed:
communication, however, the actual speed is 31,200 to 21,600 bps in most cases. If the line
status is extremely bad, the speed may be even as low as 9600 bps. The communication
speed is determined by a transmission terminal according to the result of phase 2 in V.34.
Therefore, even when the same line is used, the communication speed varies with the
transmission terminal.
Line frequency characteristic (F characteristic): The characteristic of a telephone line about
frequency is called "frequency characteristic." The characteristic ideally should be uniform in
the speech band from 300 to 3400 Hz but usually deteriorated at at high and low frequencies
of a public line (attenuation distortion or signal delay not affecting a speech). The longer the
ground distance (more precisely, the line distance of the analogue section) becomes, the
worse the deterioration becomes. Compared with ordinary voice or G3 Fax communication,
Super G3 communication is greatly affected by the frequency characteristic. Even a line
available for normal communication at 14,000 or 9600 bps may cause errors in Super G3
communication. Since most corporate leased lines (digital lines) use voice compression, their
frequency characteristics are worse than those of NTT public lines. Therefore, the error
occurrence rate goes high in Super G3 communication.
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Since Super G3 Fax uses analog communication, the signal level is very
The maximum speed is 33,600 bps in Super G3 mode.
CHAPTER 2 TROUBLESHOOTING
In domestic PSTN
Level 2 Troubleshooting