Asynchronous Multiplexer Mode; 9 B E Sc Backward Alarms - Comtech EF Data DMD50 Installation And Operation Manual

DMD50 Universal Satellite Modem
Bit 4 Multiframe Message
Spare
Bits 5 and 6
Bits 7 and 8 Encryption
Utilization
The ratio of the Through Terrestrial Data Channel Rate to the aggregate rate is 15/16. The
standard transmit and receive channels of the ES to ES Data Channel in Standard IBS Mode are
raw channels operating at the specific bit rate as controlled by the data channel rate, without
buffering. In addition, no clocks are provided with this channel. Since it would be rare that the
data rate provided was exactly that required for a standard rate device, the only method of
communicating using this channel is to allow it to super-sample the user data.

3.12 Asynchronous Multiplexer Mode

Since many of the frame bits in the standard IBS mode are not used, an "Enhanced" Multiplexer
Mode has been implemented that can be engaged under software control. Since this mode
changes the use of many of the framed non-data bits, this mode is only usable when the DMD50
is at both ends of a link.
In this mode, the overhead signaling bytes 16 and 48 can be used to implement a significantly
higher speed ES to ES Data Channel under software control. When implemented, this rate is 16
times that of the normal IBS standard, or 1/30
rate).
The IBS Async mode MUST be selected for true Asynchronous channel
operation to be available.
3.13 ESC Backward Alarms
When running in IDR Mode and if the modem has the ESC Option, there will be four Backward
Alarms available for use by the earth stations at each end of the link (both ends must have the
ESC option). These alarms are accessed via the ESC ALARMS Port. The four alarms are
controlled by four relays, each having a normally open, normally closed, and a common
connection. The common connections of these relays (referred to as Backward Alarm Inputs) can
be connected to whichever system on the earth station that the user wishes to trigger the backward
alarm.
When ground is applied to the Common (Input) Connection of one of these relays, that relay and
associated backward alarm will then be in a "no fault" state. When the ground is removed, the
relay and the associated Tx Backward Alarm will toggle to the faulted state. When in the faulted
MN-DMD50– Revision 3
As per IBS.
Not currently utilized.
Not currently utilized.
th
of the terrestrial data rate (1/32
Theory of Operation
nd
of the aggregate
3–19