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Chapter 4 Selecting the media bay modules for your system 63
Installation and Maintenance Guide
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/
ASM8+. 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/ASM8+ modules can only be installed on two offsets on a DS30 set to PPD. However, on a
DS30 in FDD, ASM8/ASM8+ 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.
Figure 26 Offsets are part of DS30 line/DN groups
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.
1 DS30 bus supports:
16 lines (trunks)*
Offset 0
Offset 1
Offset 2
Offset 3
Each offset supports:
four lines (trunks)*
*DTM: 6 to 8 lines per offset (24 to 30 lines per DS30)
*FEM: DS30 = 1 port
four DNs (single density)
eight DNs (double density)
16 DNs/32 time slots (Partial Double Density)
32 DNs/32 time slots (Full Double Density)