Terrestrial Framing - Drop Mode/Insert Mode; Insert Terrestrial Frame Source - Comtech EF Data DMD50 Installation And Operation Manual

DMD50 Universal Satellite Modem
H.2.3 Terrestrial Framing - Drop Mode/Insert Mode
The Drop Mode Selection and the Insert Mode Selection identify the Terrestrial Data-Framing
Format. As previously mentioned, their selection is influenced by the Modulator and
Demodulator Data Rates, and trying to select a T1 Type Framing Format with a data rate of
1920000 bps will result in an error message. In turn, the selection of the terrestrial framing
formats influences the satellite channel to terrestrial timeslot mappings in the following manner:
The selection of T1-D4, T1-ESF, or SLC-96 type terrestrial framing format limits the
terrestrial timeslots to values from 1 - 24.
The selection of PCM-30 or PCM-30C type terrestrial framing limits the terrestrial timeslots
to values from 1 - 15, 17 - 31. In these modes, terrestrial timeslot 16 is reserved for ABCD
signaling and may not be dropped or inserted.
The selection of PCM-31 or PCM-31C type terrestrial framing limits the terrestrial timeslots
to values from 1 - 31. Therefore, the terrestrial framing format should be identified via the
Drop Mode and Insert Mode entries prior to editing the Drop or Insert satellite channel to
terrestrial timeslot maps.
H.2.3.1

Insert Terrestrial Frame Source

The Insert Terrestrial Frame Source selection tells the Modem from where the Insert Terrestrial
Frame is coming.
External:
Internal:
The selection of the Insert Terrestrial Frame Source also influences the Buffer Clock selection in
the following manner:
When the Insert Terrestrial Frame Source selection is set to External, the received satellite data
will be clocked out of the Doppler Buffer based upon the clock recovered from the insert data
input. Therefore, the Buffer Clock selection will automatically be set to External and cannot be
modified. Attempts to select a different buffer clock will result in the error message INVALID
BUFFER CLOCK and the selection will not be allowed.
When the Insert Terrestrial Frame Source selection is set to Internal, the operator needs to
specify how data should be clocked out of the Doppler Buffer. In this case, the operator will be
able to select SCTE, SCT, RX SAT, or EXT EXC as the source for the Buffer Clock. Therefore,
the Insert Terrestrial Frame Source selection should be made prior to attempting to change the
Buffer Clock. In most instances, the Insert Terrestrial Frame Source selection will be set to
External and the Buffer Clock will automatically be set to External.
MN-DMD50– Revision 3
Indicates that the terrestrial frame is to be input via the Insert Data In
Port.
Indicates that the modem needs to generate the terrestrial frame and that
all non-inserted timeslots need to be filled with the appropriate idle code
based upon the terrestrial framing (T1 or E1).
Drop and Insert (D&I)
H–10