Overview of ISDN BRI Interfaces

Basic concepts of ISDN BRI Interfaces

Integrated Services Digital Network (ISDN) evolves from the Integrated Digital Network (IDN). The Integrated Services Digital Network (ISDN) provides end-to-end digital connections and supports a wide range of services, including voice, high-speed fax, video phone, intelligent telegraph, and teletext services.

ISDN provides users with a set of user-network interfaces (UNIs) to connect different terminals such as phones, fax machines, and computers to ISDN networks. ITU-T I.412 defines two types of interfaces: Basic Rate Interfaces (BRI) and Primary Rate Interfaces (PRI).

• A BRI interface contains two 64 kbit/s B channels and one 64 kbit/s D channel (BRI interface bandwidth = Bandwidth of two B channels + Bandwidth of one D channel). The two B channels (B1 channel and B2 channel) can be used independently or be bundled by using the MP technique to provide a maximum of 128 kbit/s transmission rate.

• PRI interfaces are classified into CE1/PRI interfaces and CT1/PRI interfaces: For the configuration of a CE1/PRI interface, see CE1/PRI Interface Configuration; for the configuration of a CT1/PRI interface, see CT1/PRI Interface Configuration.

Both BRI and PRI interfaces contain data channels (B channels) and signaling channels (D channels). B channels transmit data of upper layer applications, and D channels transmit all ISDN signaling packets.

Attributes of ISDN BRI Interfaces

ISDN BRI interfaces have the following characteristics:

• Comply with the S/T interface standard.
• Use PPP and FR as link layer protocols.
• Use IP as the network layer protocol.