Standard Ibs Mode; Asynchronous Multiplexer Mode; Esc Backward Alarms - Radyne DMD15 Installation And Operation Manual

Operation

3.21 Standard IBS Mode

In the first or "Normal" mode, all bit assignments are per the IBS standard. The bits of Overhead
Housekeeping byte 32 are implemented as shown in Table 3-4 below:
ES to ES Data
Bit 1
Channel
Bit 2 Frame Alignment
Bit 3 Backward Alarm
Multiframe Message
Bit 4
Spare
Bits 5 and 6
Encryption Utilization
Bits 7 and 8
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.

3.22 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 DMD15
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
nd
rate (1/32 of the aggregate rate).
Note: The IBS Async mode MUST be selected for true Asynchronous channel operation to
be available.

3.23 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 state, the receive end of the link will receive that backward alarm that
is initiated at the transmit end of the link.
3-26
DMD15/DMD15L IBS/IDR Satellite Modem
Table 3-4.
This bit is routed directly to the ES to ES Data Channel.
th
Its data rate is 1/512 of the aggregate rate (or 1/480
the through terrestrial data rate), and is normally used to
super-sample an asynchronous data channel.
Part of the Frame Alignment word.
Transmit and Receive with main processor to activate
Main Alarm/LED.
As per IBS.
Not currently utilized.
Not currently utilized.
th
of
th
of the terrestrial data
TM051 – Rev. 5.8