Telephone User Manual

ISDN Interfaces
RBSU/RBSS Interface Units
Strata CTX I&M 06/04 7-15
ISDN Interfaces
The RBSU, and/or RBSS circuits that connect to the Strata CTX station side, (BRI-NT, S-
reference point) allows direct connection of multiple ISDN (TE-1 or TA) devices. The S point of
the RBSU/RBSS supports the Toshiba Strata CTX passive bus, also known as point-to-multipoint
connection. The terminal-side (S-point) of the RBSU/RBSS BRI circuit can have parallel
connections of up to two TE-1s or TAs maximum.
When multiple TE-1 and TA devices are installed on a single RBSU/RBSS BRI circuit, the devices
must share, or contend for, that circuit’s two B-channels. That is to say, a maximum of two
simultaneous voice and/or data calls are allowed between both devices connected to the same BRI
circuit. The contention rule for the two BRI B-channels is first come, first serve.
Figure 7-9 RBSU/RBSS Interfaces between the S/T Reference Points
Capacity and Cabinet Slot Information
The RBSU/RBSS can be installed in any slot except in a slot that has been left vacant to provide
capacity for RDTU, BPTU or RPTU2 or RPTU as shown in Table 2-54 on page 2-39 and Table
2-55 on page 2-40. Each RBSU and/or RBSS contains two circuits and each circuit reduces the
system capacity by two station ports and two CO lines (one port/line per B-channel). Therefore, if
the RBSU PCB is installed, the station port and CO line count will increment by four ports and
four lines at the RBSU cabinet slot.
If the RBSU/RBSS is installed, the station port and CO line count will increment by eight station
ports and eight lines at the RBSU/RBSS cabinet slot. RBSU and RBSS PCBs can be installed in
any combination so long as the number of RBSU PCBs is the same or greater than the number of
RBSS PCBs. See “ISDN BRI Digital Station PCBs” on page 2-41 and “Worksheet 3: CO Line” on
page 2-25 for the maximum BRI circuits allowed.
RX
TX
DK TBSU or
RBSU/RBSS
NT1
RX
TX
PSTN
RX/TX
UTS
BRI
(2-wire)
BRI-TE
(4-wire)
BRI-NT
(4-wire)
3336
S, T, and U are ISDN reference points.
TE = S-type Terminal Equipment
TA = S-type Terminal Adaptor
TE-1
or
TA
1
2
...
TE-1
or
TA