64 Chapter 4 Selecting the media bay modules for your system
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Default BCM 3.0 and newer systems are configured as Partial Double Density (PDD) systems, in
that they maintain DS30 06 and 07 in the original configuration of 16 DNs per bus. This
accommodates those systems which use Companion. The system can be set to Full Double Density
(FDD) at system startup or once the system is setup. When the system is set to FDD, DS30 06 and
07 allow access to the second set of DNs, and they are no longer available for Companion
operation.
Setting Offsets
Each offset is one-quarter of a DS30 bus. Each DS30 bus, supports 16 lines (32 time slots) for
most trunk modules.
Exceptions:
• DTM modules support 23 to 30 lines per bus
• FEM modules, where each DS30 bus supports one Norstar fiber module connection.
For station modules, each bus supports 16 telephones or telephony devices for station modules that
support single density, or which are set to single density, in the case of the DSM16+ and DSM32+,
or on DS30 06 and 07 if the system remains set to Partial Double Density (PDD). On each bus that
supports double density, DSM16+ and DSM32+ modules set to double density have access to
eight telephones per offset, for a total of 32 telephones per DS30 bus if the offsets are fully loaded.
Offsets are numbered 0, 1, 2, and 3. Modules that require less than a full DS30 bus can be assigned
a DS30 bus number and an offset number. This allows more than one module to be assigned the
same DS30 bus number, but with a different offset number.
Modules that can have offsets assigned include CTM, CTM8, GATM4, GATM8, BRI, and ASM 8/
GASM8. For example, two CTM 8s can be assigned to the same DS30 bus number, with different
offset numbers. However, you cannot assign a CTM8 and an BRI module to the same DS30 bus.
ASM8/GASM8 modules can only be installed on two offsets on a DS30 set to PPD. However, on a
DS30 in FDD, ASM8/GASM8 modules can be supported on all four offsets. Note that there is no
double-density dip switch setting for these modules.
Offsets are assigned using DIP switches 1, 2, and 3 on the media bay module.
Figure 26 shows how a DS30 bus containing 16 line connections is broken down into four offset
groups of four lines each.
Note: Devices that share a DS30 bus must be identical. Use two DSM 16+ modules set
to double density on a single DS30 bus.
A DSM 32+ set to double density requires a full DS30 bus.
Note: Media bay modules that do not or cannot share DS30 bus blocks always assign the
offset as 0 (zero). As well, if the module requires more than one DS30 bus, such as the
4x16 module, only the first DS30 bus is set on the DIP switches. The next consecutive
DS30 bus number is automatically assigned by the module.
