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Option Selection
in an Installation
with a MAU-1A
• Out-of-band communication — the alternate means of
with the CSU, that does not depend on the T1 link to the CSU. Out-of-
band communication with the CSU is typically made via modems or a
Supervisory terminal co-located with the CSU. It is intended for per-
forming diagnostics that would disrupt in-band communication
as a loopback) and for accessing the CSU when a T1 link failure pre-
vents in-band communication. A typical out-of-band communication
path is illustrated in Figure 2-5.
Configuring a CSU as a slave CSU assures that a Supervisory
user cannot make configuration changes, regardless of the communica-
tion path, that could disrupt in-band communication. A slave CSU dis-
plays a warning message when the user attempts to configure it or per-
form a self-test or loopback, although it does not prevent these tests. Refer
to Electrical Connections for additional installation information.
This manual applies only to assembly-level Revision (P) and LATER
DataComm 551 pc cards. You must use Publication No. 048R137-800 for
Revision (N) and EARLIER pc cards. However, the newer DataComm 551
is backward-compatible with the older version, so you can install it in
your existing system.
The major improvement is PMC-100 support, eliminating the need for us-
ing MAU-1As and fallback switches for Supervisory terminal communi-
cations. When replacing an older DataComm 551 with a newer one, note
the following option switch changes:
Switch
Old Label
S6-1
BDA
S6-2
BDB
S6-3
BDC
S6-6
CF3
S4-6
AD5
S4-7
AD6
S4-8
SLAVE
S7-4
MLBO
New Label
BDA
BDB
PMC
SLAVE
AD5
AD6
AD7
ALBO
INSTALLATION
communicating
(such
terminal
2-9
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