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PSM-500/500L/500LT SCPC Satellite Modem
The un-terminated versions of these standard interfaces and are used to implement one for one
(1:1) redundancy between two PSM-500 units.
A single 37 pin "D" type female connector is available on the rear panel at J3 providing the terrestrial
data interface. The interface standard is electronically selectable via front panel or remote control.
Optional interfaces are provided by a separate option interface card which is mounted inside the
modem chassis. The provision of an optional interface "adds" to the available interfaces which can
be selected under program control. An interface field kit of parts to add an option interface is
available from the manufacturer for installation by qualified technical field service personnel. When
an optional interface is installed the main processor automatically queries and installs the necessary
software controls for accessing the interface.
1.2.6.1 Data Interface Loop-Back Function
The standard and most optional interfaces also provide the data loop-back function. Ethernet
interfaces do not have this function. The data loop-back can be controlled from the front panel or via
remote control command. The data towards both the terrestrial and satellite sides can be looped
back individually by enabling this function via the front panel or remote control
⇒
Caution: Enabling the "Data Loop-Back" functions will result in loss of traffic. It
should not be used in operating links without prior arrangements.
The data loop-back allows testing of the signal path connection up to the loop-back and back to the
source. Since both terrestrial and satellite sides of the signal path can be looped, the connection
from a local DTE can be checked on the terrestrial side while the connection from the far end DTE
over the satellite and through the modem can be checked on the satellite side.
More information on use of the loop-back modes is given in Section 4.1 Common Test Procedures.
1.2.6.2 Data Interface BERT Function
The standard interfaces also include a programmable Bit Error Rate Test (BERT) set. It is located
between the modem's satellite and terrestrial data loop-back functions. Ethernet interfaces do not
have this function. The BERT can be controlled from the front panel or via remote control command
and provides extensive test result data.
⇒
Caution: Enabling the "BERT" function will result in loss of traffic. It should not be
used in operating links without prior arrangements.
New in this modem is the ability to set the BERT set to point toward the "Line" side external cabling,
acting as a DCE device. More on use of the BERT functions and modes is given in Section 4.1.2
"Using the Built-in BERT".
1.2.6.3 Data Interface 1:1 Redundancy Function
The standard interfaces are also capable of operating in a special 1:1 redundancy mode. In this
mode the data interfaces are tied directly in parallel using a special "Y" cable. Software control built
into the modem can then be set to indicate that the two connected modems are operating in a
redundant mode. The two modems communicate with each other to determine the alarm status of
each and force the "off-line" unit's data interface into an un-terminated condition. This allows both
interfaces to receive incoming data and clock signals, which are necessary to ascertain correct
functioning. At the same time the transmit and receive IF ports are also connected together through
the stations (or separately supplied) transmit and receive IF combiner/splitter assemblies.
The alarms that are used to determine switching criteria are programmable, and the first modem set
up for this mode automatically loads its configuration information to the second or "back-up" unit.
These features create a very low cost redundancy system that is both flexible and easily set up.
More information on the set-up and use of the 1:1 redundancy functions and modes is given in
Sections 2.3.5 "1:1 Redundancy Connection" and 3.10 "Built-in 1:1 Redundancy Mode Operation".
PSM-500/500L/500LT - Rev. 0.91
Description
Page 1-13
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