Xerox WorkCentre Pro 423 Service Manual Download

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03/02

Level 2 Troubleshooting

WorkCentre Pro 423/428

2-75

CHAPTER 2 TROUBLESHOOTING

2.3.2 Troubleshooting in ISDN communication

ISDN is integrated from subscriber telephone, 64 Kbps circuit switched, and packet switched
networks. In Japan, NTT is providing two services, NET-64 and NET-1500. The other Class-
1 carriers (TTNet, etc.) are also providing services based on the same technical standard.
(Some ISDN services outside Japan use different technical standards but appropriate
conversion enables intercommunication. For example, the speed is 56 kbps in the U.S.
mainland.

ISDN physically has several logical channels in one line. Three channels in total (one D
channel and two B channels) are available from NET-64 and up to 24 channels from NET-
1500. ISDN also supports various other configurations. If NET-1500 is connected to a G4
Fax (always through PBX), its service is almost the same as that of NET-64 (however, B
channel may be one).

In ISDN communication, the D channel is used to originate, terminate, and clear calls in G4
Fax, G3 Fax, and call modes and the B channels are used to exchange information with
remote terminals. Therefore, what is most important in troubleshooting is to locate a
communication error in the D channel (or earlier physical fault) or B channels. An error code
identifies the D or B channels.

The error status is checked on protocol monitors. The D-channel protocol monitor is ICM.
The B-channel protocol monitors are Link Layer (Layer 2), Network Layer (Layer 3), Transport
Layer (Layer 4), Session Layer (Layer 5), and Presentation Layer (Layer 6).

For troubleshooting, the error is located in the D or B channels with the displayed error code
and the corresponding protocol monitor data is ejected for checking and analyzing signal
exchange and contents. Then corrective and recovery actions are taken according to the
results. Details of the signals are recorded in FIF.

Through ISDN, NTT is providing an increasing number of additional services. The
representative additional services are dial-in, calling number indication (Number Display),
facsimile communication network, Voice Forward Service. Even functions named subscriber
telephone networks (analogue public line networks) provide services of different contents.
Since an ISDN line with these additional services is subject to communication errors unique to
these services, the client or carrier should check the contents of contract (dial 116 for NTT).

In ISDN communication outside Japan, incoming signals from overseas may be different from
those explained here because the technical standards partially differ.

This troubleshooting section consists of:

1. ISDN Line Basic Troubleshooting Flow

2. ISDN Basic Sequences (D-channel and B-channel sequences)

3. D-channel Troubleshooting (Signal list, DISC/STATUS/SETUP signals, and reason display
value)

4. B-channel Troubleshooting (Network, Session, and Presentation protocols)

Precautions on Parameter Settings and Cases of Problems

Subsections 3 and 4 explain fax troubleshooting about frequently used signals.
For FIF of each signal, see "FIF of DISC signal" below. A signal explained in 3
or 4 may have FIF shorter (with only information elements necessary for
communication) or longer (with information elements not explained here) than
the one below.

Xerox WorkCentre Pro 423, Service Manual

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