Configuring T3 Interfaces

To configure properties on a T3 (DS3) interface:

  1. From the configuration page, as shown in Figure 1, select the T3 interface you want to configure.

    The properties you can configure on a T3 interface are displayed, as shown in Figure 8.

    Figure 8: T3 Interfaces Configuration Page

    T3 Interfaces Configuration Page
  2. Enter information into the configuration page, as described in Table 11.
  3. Click one of the following buttons:
    • To apply the configuration and stay on the Configure Interfaces page, click Apply.
    • To apply the configuration and return to the configuration page that lists all interfaces, click OK.
    • To cancel your entries and return to the Configure Interfaces page, click Cancel.

Table 11: T3 Configuration Summary



Your Action

Logical Interfaces

Add logical interfaces

Defines one or more logical units that you connect to this physical T3 interface. You must define at least one logical unit for a T3 interface. You can define multiple units if the encapsulation type is Frame Relay.

Click Add.

Logical Interface Description

(Optional) Describes the logical interface.

Type a text description of the logical interface to more clearly identify it in monitoring displays.

IPv4 Addresses and Prefixes

Specifies one or more IPv4 addresses for the interface.

  1. Click Add.
  2. Type one or more IPv4 addresses and prefixes. For example:

  3. Click OK.

Physical Interface Description

(Optional) Adds supplementary information about the physical T3 interface.

Type a text description of the T3 interface to more clearly identify it in monitoring displays.

MTU (bytes)

Specifies the maximum transmission unit (MTU) size for the T3 interface.

Type a value between 256 and 9192 bytes. The default MTU for T3 interfaces is 4474.


Specifies the transmit clock source for the T3 line.

From the list, select one of the following:

  • internal—Device's own system clock (the default)
  • external—Clock received from the T3 interface

Per Unit Scheduler

Enables scheduling on logical interfaces.

Allows you to configure multiple output queues on a logical interface and associate an output scheduler and shaping rate with the queues.

  • To enable scheduling, select the check box.
  • To disable scheduling, clear the check box.


Specifies the encapsulation type for traffic on the interface.

From the list, select the encapsulation for this T3 interface:

  • PPP
  • Frame Relay
  • Cisco HDLC

Enable CHAP

Enables or disables CHAP authentication on a T3 interface with PPP encapsulation only.

  • To enable CHAP, select the check box.
  • To disable CHAP, clear the check box.
CHAP Local Identity (available if CHAP is enabled)

Use System Host Name

Specifies that the T3 interface uses the device's system hostname in CHAP challenge and response packets.

  • To enable, select the check box (the default).
  • To disable, clear the check box.

Local Name

If Use System Host Name is disabled, specifies the local name for CHAP to use.

Type a local name for this T3 interface.

CHAP Peer Identity

Identifies the client or peer with which the device communicates on this T3 interface.

Type the CHAP client name.

CHAP Secret

Specifies the secret password for CHAP authentication, known to both sides of the connection.

Type a password that is known to the other side of the connection. Use a combination of letters and numbers that is difficult for others to guess.

T3 Options

Frame Checksum

Specifies the number of bits in the frame checksum. A 32-bit checksum provides more reliable packet verification, but is not supported by some older equipment.

Select 16 or 32. The default value is 16.

Enable Long Buildout

Specifies a short or long cable length for copper-cable-based T3 interfaces. A long cable is longer than 225 feet (68.6 m).

  • To enable long buildout, select the check box.
  • To disable long buildout, clear the check box.

Disable C-Bit Parity Mode

Enables or disables C-bit parity mode, which controls the type of framing that is present on the transmitted T3 signal.

  • To disable, select the check box.
  • To enable, clear the check box.