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CHAPTER 8: Link Configuration
77
8.7 The X.21 Link
INTRODUCTION TO X.21
Unlike the mux links (leased-line links), which are
permanently connected, X.21 is a pay-as-you-go link.
When a signal is raised, the network automatically
establishes the link to the remote side. When you
are finished, the link is dropped until it is again
needed. The link is established on demand. X.21 is
for data-only channels; it does not support voice or
fax channels. In X.21 link operation, the
Multiserver must be connected (via the PTT-
provided line terminator) to a feeder mux (not
another Multiserver).
This X.21 application (X.21 bis) is designed for
Automatic Direct Call across an X.21 bis network.
Automatic Direct Call means that any data or signal
(DTR) activity on any Multiserver channel
configured for X.21 applications causes the
Multiserver to signal the network to initiate a call.
Only one call route is required. Calls initiated
locally and remotely (at the mux end) have the
capacity to switch and contend for resources on the
Multiserver.
P
ORT CONFIGURATION FOR THE X.21 LINK
Select option 5 on the Port Configuration Menu.
A clocking message will not display; X.21 clocking is
provided externally. You will be returned to the
Configure Local Nodes Menu.
Important
The Multiserver must be node-reset (to
current configuration) after the port
has been configured for an X.21 link.
CONFIGURATION OF X.21 LINK PARAMETERS
After configuring the port for an X.21 link, the
X.21 link parameters must be set. Select option 14
(X.21 Link Parameters) of the Configure Local
Nodes Menu.
You will be prompted:
If the port is not configured as X.21, you will receive
an error message:
** NOT X.21 LINK **
Most likely, a node reset was not done after the port
was configured for the X.21 link. Do a node reset
and access this menu again.
The X.21 Link Parameters Menu then appears (see
next page). Each of the menu options is discussed
in detail in Table 8-2.
After the X.21 Link Parameters are configured,
perform a link reset. (See Section 11.1, Reset, and
Table 11-1, Reset Options, for further information.)
After resetting, the Multiserver will exchange
information with the feeder mux and,
approximately 20 seconds later, the link will drop
until an X.21 call is initiated.
The CCM indicator lights do not reflect the X.21
link status. The Command Facility Node Status
display will show the link status (see Section 8.8,
Review Link Configuration).
CONFIGURE LOCAL NODES [node id]
X.21 LINK PARAMETERS
14
ENTER NODE-ID/CHANNEL #
(^X TO ABORT):
PORT CONFIGURATION [xxx]
X.21 LINK
5