ABSTRACT: This document addresses the protocol and procedural requirements on the local switching system for serving Integrated Services
Digital Network (ISDN) Basic Rate Interface (BRI) customers. It addresses call establishment and clearing procedures for signaling
over the user-network interface and interworking with existing networks. Interexchange ISDN calls are not covered except for packet
mode calls and those calls that connect to non-ISDN users (i.e., users who are served through analog telephone lines, covered in
TR-NWT-000444,Switching System Requirements Supporting ISDN Access Using the ISDN User Part). Calls to non-ISDN users are
referred to as interworking calls.
This document emphasizes basic call establishment procedures such as call setup, call progress treatment, connect, answer, and
disconnect. Circuit-mode and packet-mode call procedures are defined. This document provides requirements for the National ISDN (NI)
platform. It also contains requirements that are currently not supported by NI. This document is based on the fundamental concepts
described in the ITU-T1-series Recommendations.
The following documents were fully or partly replaced by GR-268: TR-TSY-000268, TR-TSY-000268-SUP01, TA-TSY-000035, TA-TSY-000790,
TA-TSY-000791, TA-TSY-000792, TA-TSY-000794, TA-TSY-000795, and TA-TSY-000880, TR-TSY-000268 is erroneously referred to as
"TR-TSY-000286" in GR-505; GR-268 is now the right reference.