Telephone User Manual

ISDN Interfaces
BPTU/RPTU Overview
Strata CTX I&M 06/04 7-3
ISDN Interfaces
BPTU/RPTU Overview
Both the BPTU and RPTU provides 24 channels for ISDN PRI service. The BPTU is fully
compatible with RDTU2 and will replace the RPTU. Network connection using BPTU or RPTU
PRI interface requires installation of a customer-provided CSU in most locations of the U.S. Refer
to “CSU Requirements” on page 7-3 for CSU installation.
The BPTU or RPTU is a DS-1 divided into 24 TDM channels using standard T1 electrical signal
format. The BPTU or RPTU’s D-channel is typically the 24th channel and can control the
signaling of 23 of its own B-channels and 24 B-channels of another designated BPTU or RPTU.
Each BPTU or RPTU can also use its own D-channel for control.
The BPTU or RPTU’s in-service bit rate is 1.544 mbps (± 4.6 ppm), but during a maintenance
session, the rate may vary ± 32 ppm. The BPTU or RPTU provides Binary 8-Zero Substitution
(B8ZS) and ESF with Framing Pattern Sequence (FPS) and Cyclical Redundancy Check (CRC)
error checking in the framing bits.
Extracting the Stratum-1 clock from the ISDN PRI, BRI, or T1 provider is the most common
method used to synchronize the BPTU or RPTU PCB and the Strata CTX time switch to the public
telephone network. One BPTU, RPTU, RBSU, RBUU, or RDTU T1 must extract the clock from
the ISDN or T1 provider. The selected unit is designated as the “Primary” timing source in
Program 105. In remote cabinet applications, the Primary clock source PCB must be installed in
the Base Cabinet (main location). For more information, refer to “Timing and Synchronization” on
page 7-35.
A dealer-supplied CSU must be installed between the ISDN PRI network line and the BPTU or
RPTU PCB as shown in Figure 7-1. Some telephone companies supply the CSU and call it the
Network Interface Unit (NIU).
CSU Requirements
In the U.S., the CSU must be UL listed and comply with Part 68 of the FCC rules. It must also
comply with the limits for a Class A digital device, pursuant to Part 15 of FCC Rules. In Canada,
the CSU must be CSA certified.
The CSU is transparent to data, clock, and framing. It acts as a repeater, not a controller, for
timing. The CSU also acts as a signal regenerator and must be able to perform loop-back tests and
maintenance to both the network and Strata CTX BPTU or RPTU. The CSU is the same type as
used for T1 circuits although it performs the function as NT1 for PRI ISDN in the ISDN reference
model as shown in Figure 7-1.
Slot Assignments
Up to eleven BPTU or RPTU PCBs can be installed in a Strata CTX system providing up to 264
PRI lines (B-channels). If BPTU or RPTU (PRI) and RDTU (T1) PCBs are installed, the maximum
combined PCBs cannot exceed eleven. The PCBs must be placed in designated slots in each of the
cabinets. Refer to Chapter 2 – Strata CTX Configuration, “ISDN PRI Digital Line PCBs” on page
2-40, for the guidelines regarding BPTU or RPTU PCB slot assignments.