This International Standard specifies the service description and control aspects, including functional capabilities and information flows, of standardised circuit-mode bearer services which may be supported by a Private Integrated Services Network (PISN).

This International Standard includes the following basic services:

• Circuit-mode 64 kbit/s unrestricted 8 kHz structured bearer service category;
• Circuit-mode 64 kbit/s 8 kHz structured bearer service category usable for speech information transfer;
• Circuit-mode 64 kbit/s 8 kHz structured bearer service category usable for 3,1 kHz audio information transfer.

A PISN shall support at least one of the above three bearer services to conform with this International Standard.

The scope of this International Standard does not include:

• the negotiation of service at call establishment time,
• the change of service during a call, and
• unidirectional services.

This International Standard includes optional procedures for the provision of functions equivalent to the following public ISDN supplementary services: Subaddress and Multiple Subscriber Number.