ISDN Overview

Integrated Services Digital Network (ISDN) is a set of standards for digital transmission over different media created by the Consultative Committee for International Telegraph and Telephone (CCITT) and International Telecommunication Union (ITU). As a dial-on-demand service, it has fast call setup and low latency as well as the ability to carry high-quality voice, data, and video transmissions. ISDN is also a circuit-switched service that can be used on both multipoint and point-to-point connections.

You configure two types of interfaces for ISDN service: at least one physical interface and a logical interface called the dialer interface.

ISDN Interfaces

The following interfaces on a device are available for ISDN connectivity:

• For ISDN BRI, up to six of the following field-replaceable units (FRUs):

  • 4-port S/T PIM supporting ITU-T I.430, ETSI TS 101080, and GR-1089-Core Type III
  • 4-port U PIM supporting ANSI T.601 and GR-1089-Core
• For ISDN PRI, up to six Dual-Port Channelized T1/E1/ISDN PRI PIMs, supporting ITU-T Q.920, Q.921: LAPD, Q.930, and Q.931

ISDN BRI Interface Types

A J Series device with one or more ISDN BRI ports has the following types of ISDN interfaces:

• Physical ISDN BRI interface—br-pim/0/port
• Physical B-channel interface—bc-pim/0/port
• Physical D-channel interface—dc-pim/0/port
• Logical dialer interface—dln

For information about interface names, see Network Interface Naming.

To configure ISDN BRI service on a J Series device, you configure the physical ISDN BRI interface and the logical dialer interface.

Each ISDN BRI port has two B-channels for transport, identified as bc-pim/0/port:1 and bc-pim/0/port:2, and one D-channel for control, identified as dc-pim/0/port. On ISDN BRI interfaces, the B-channels and D-channel have no configurable settings, but you can monitor them for interface status and statistics.

ISDN PRI Interface Types

On a J Series device with one or more Dual-Port Channelized T1/E1/ISDN PRI PIMs, you can configure each port on the PIM for either T1, E1, or ISDN PRI service, or for a combination of ISDN PRI and either T1 or E1 service. For ISDN PRI service, you configure the following types of ISDN interfaces as channels on the channelized T1 or E1 interface:

• Physical B-channel interface—bc-pim/0/port:channel
  • On a channelized T1 interface, up to 23 time slots can be configured as ISDN PRI B-channels.
  • On a channelized E1 interface, up to 30 time slots can be configured as ISDN PRI B-channels.
• Physical D-channel interface—dc-pim/0/port:channel
  • On a channelized T1 interface, you configure time slot 24 as the D-channel.
  • On a channelized E1 interface, you configure time slot 16 as the D-channel.
• Logical dialer interface—dln

For information about interface names, see Network Interface Naming.

For more information about channelized T1/E1/ISDN PRI interfaces, see Configuring Channelized T1/E1/ISDN PRI Interfaces.

Dialer Interface

The dialer (dln) interface is a logical interface on which you configure dialing properties for ISDN connections. The interface can be configured in two modes:

• Multilink mode using Multilink PPP encapsulation
• Normal mode using PPP or Cisco High-Level Data Link Control (HDLC) encapsulation

The dialer interface can perform backup, dialer filter, and dialer watch functions, but these operations are mutually exclusive. You can configure a single dialer interface to operate in only one of the following ways:

• As a backup interface—for one primary interface
• As a dialer filter
• As a dialer watch interface