Strata CTX I&M 10/02 5-1
ISDN Interfaces
ISDN Interfaces 5
This chapter covers information on the ISDN Primary Rate Interface (PRI) and Basic Rate
Interfaces (BRI).
PRI Overview
For PRI services, the Strata CTX uses an RPTU PCB to connect to a Public Switched Telephone
Network (PSTN) PRI line using a UL listed (or CSA certified in Canada) Channel Service Unit
(CSU) in most locations in the U.S. Each RPTU provides 23B + D channels. The
B-channels support CO speech and data connections on the PSTN side only. The RPTU PCB is
shown in Figure 5-1 on page 5-2.
The Strata CTX also uses the RPTU2 PCB to connect StrataNet QSIG network nodes using
DS-1. A DS-1 may be obtained in several ways, most commonly, leasing it from a carrier.
BRI S/T Overview
BRI S/T is available with the RBSU PCB. The RBSU provides two BRI S/T circuits to connect to
the PSTN BRI line using an external UL listed NT1; or, on the station-side, connect to:
• S-type ISDN telephones and Terminal Equipment (TE-1-S)
• S-type Terminal Adapters (TA-S) with non-ISDN devices
Each TE-1-S and TA1-S device can support voice and/or RS-232 switched-circuit data as shown in
Figure 5-1. The station-side BRI S/T circuits are point-to-multipoint.
A subassembly (RBSS) can be attached to the RBSU for two additional BRIs for S-type station-
side connections only. The RBSU PCB and the RBSS subassembly are shown in Figures 5-9 and
Figure 5-10 on page 5-14. The combination of RBSU and RBSS uses only one slot to provide up
to four BRI S/T circuits.
Note Each installed RBSU or RBSS circuit provides a 2B + D connection and uses a system
capacity of two station ports and two CO lines regardless of the circuit application, even if
the circuit is not actually connected.
BRI U Overview
For BRI U services, the RBUU provides two BRI U circuits that connect directly to PSTN BRI
lines; or, on the station side, connect to:
• U-type ISDN telephones and Terminal Equipment (TE-1-U)
• U-type Terminal Adapters (TA-U) with non-ISDN devices
Each TE-1-U and TA-U device can support voice and/or RS-232 switched-circuit data
depending on the device (see Figure 5-1). The station-side BRI U circuits are point-to-point.
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