# Configuration Tasks

Configure a T3 interface by entering Global Configuration mode and performing the following tasks:

1. Configure a T3 controller.
2. (Optional) Configure MDL settings.
3. (Optional) Configure other settings for the interface.
4. Configure HDLC channels for T3 frame and E3 frame controllers.
5. (Optional) Configure fractional T3 for T3 frame controllers.
6. Use the appropriate show commands to verify your configuration.

E3 interface configuration tasks are identical to T3 interface configuration tasks, except that the CLI commands contain e3 instead of t3.

For example, you configure an E3 controller with the controller e3 command instead of the controller t3 command.

## Configuring a T3 or an E3 Controller

To configure a T3 or an E3 controller:

1. Select the T3 or E3 controller from Global Configuration mode.
   host1(config)#controller t3 3/2
2. Enable the T3 or E3 controller.
   host1(config-controll)#no shutdown
3. (CT3/T3-F0 line module only) Enable unchannelized operation for this controller.
   host1(config-controll)#no channelized

channelized

- Use to enable channelized T3 operation on an interface of a CT3/T3-F0 line module.
- Example
  host1(config-controll)#channelized
- Use the no version to enable unchannelized T3 operation on an interface for a CT3/T3-F0 line module.
- See channelized.

controller e3

- Use to specify an E3 controller in slot/port format.
  - slot—Number of the slot in which the line module resides in the chassis
  - port—Number of the port on the I/O module
- Example
  host1(config)#controller e3 3/2
- There is no no version.
- See controller e3.

controller t3

- Use to specify a T3 controller in slot/port format.
  - slot—Number of the slot in which the line module resides in the chassis
  - port—Number of the port on the I/O module
- Example
  host1(config)#controller t3 0/1
- There is no no version.
- See controller t3.

shutdown

- Use to disable a T3 or an E3 controller.
- The T3 or E3 interface is disabled by default.
- Example
  host1(config-controll)#shutdown
- Use the no version to restart a disabled interface.
- See shutdown.

### Configuring MDL Messages

You can configure a T3 interface to send MDL messages. MDL messages are supported only when T3 framing uses C-bit parity, the default setting.

To configure a T3 interface to send MDL messages:

1. Specify a T3 interface.
   host1(config)#controller t3 8/0
2. (Optional) Configure the interface to operate in an MDL carrier environment.
   host1(config-controll)#mdl carrier
3. Specify the MDL messages.
   host1(config-controll)#mdl string eic "ERX1410" host1(config-controll)#mdl string fic "FG786" host1(config-controll)#mdl string lic “ Bldg 10" host1(config-controll)#mdl string pfi "Site 25" host1(config-controll)#mdl string port 0800
4. Enable transmission of MDL messages.
   host1(config-controll)#mdl transmit path-id host1(config-controll)#mdl transmit idle-signal host1(config-controll)#mdl transmit test-signal

mdl carrier

- Use to specify that an interface is used in the carrier environment.
- Example
  host1(config-controll)#mdl carrier
- Use the no version to restore the default situation, in which the interface does not operate in the carrier environment.
- See mdl carrier.

mdl string

- Use to specify an MDL message.
- Example
  host1(config-controll)#mdl string port 0800
- Use the no version to restore the default value to the specified MDL message or to all MDL messages.
- See mdl string.

mdl transmit

- Use to enable transmission of MDL messages.
- Specify the keyword path-id to transmit path identifications every second.
- Specify the keyword idle-signal to send idle signals every second.
- Specify the keyword test-signal to transmit test signals every second.
- Example
  host1(config-controll)#mdl transmit test-signal
- Use the no version to disable transmission of the specified MDL message or all MDL messages.
- See mdl transmit.

### Optional Tasks

The following configuration tasks are optional for T3 and E3 interfaces:

- Specify the cable length (T3 only).
- Change the clock source.
- Change the framing format.
- Enable cell scrambling (ATM interfaces only).
- Assign a text description or an alias to the interface.

cablelength

- Use to adjust the transmit power appropriate to the length of a T3 cable.
- Specify a cable length in the range 1–450 feet.
- The router supports two transmit powers, one for a cable length between 1–225 feet and another for a cable length between 226–450 feet. Therefore, it is not necessary to know the exact size of your cable. You only need to know if the cable size is greater than 225 feet. For example, if your cable size exceeds 225 feet, specify any number greater than 225 and less than 451.
- Example
  host1(config-controll)#cablelength 300
- Use the no version to restore the default, 0 feet.
- See cablelength.

clock source

- Use to configure the transmit clock source for a T3 or E3 line.
- Use a transmit clock on the line’s receive data stream, except in rare cases such as back-to-back router tests. When performing back-to-back router tests, configure one end of the line as internal and the other end as line.
- Specify the keyword line to use a transmit clock on the line’s receive data stream.
- Specify the keywords internal module to use the line module’s internal clock.
- Specify the keywords internal chassis to use the router’s clock.
- Example
  host1(config-controll)#clock source internal module
- Use the no version to revert to the default, line.
- See clock source.

description

- Use to assign a text description or an alias to a T3 or E3 interface.
- You can use this command to help you identify the interface and keep track of interface connections.
- The description or alias can be a maximum of 80 characters.
- Use show controllers t3 or show controllers e3 to display the text description.
- Example
  host1(config-controll)#description westford t3 interface
- Use the no version to remove the text description or alias.
- See description.

ds3-scramble

- Use to enable cell scrambling in a T3 ATM interface.
- Example
  host1(config-controll)#ds3-scramble
- Use the no version to turn off cell scrambling on the interface.
- See ds3-scramble.

e3-scramble

- Use to enable cell scrambling in an E3 ATM interface.
- Example
  host1(config-controll)#e3-scramble
- Use the no version to turn off cell scrambling on the interface.
- See e3-scramble.

framing

- Use to configure the framing format for a T3 or E3 line.
- For a T3 line, you must specify one of the following:
  - T3 FRAME—c-bit or m23 (the default is c-bit)
  - T3 ATM—cbitadm, cbitplcp, m23adm, or M23plcp (the default is cbitplcp)
- For an E3 line, you must specify one of the following:
  - E3 FRAME—g751 or g832 (the default is g751)
- Choose a framing format that is compatible with the framing format of the network device at the other end of the line.
- Example
  host1(config-controll)#framing m23
- Use the no version to restore the default value.
- See framing.

## Configuring Fractional T3

You can configure fractional T3 on T3 frame interfaces. E3 frame interfaces do not support fractional E3.

Fractional T3 is a portion of a T3 transmission service and provides a set of lines with a speed that is greater than T1 (1.544 Mbps), but less than T3 (44.736 Mbps).

To configure fractional T3:

1. Set the DSU mode for the lines.
2. Set the speed of the fractional T3 lines.
3. Enable scrambling of the payload.

   | Caution: Complete all three steps at the same time. Otherwise, the interface might drop packets unexpectedly.

dsu bandwidth

- Use to set the speed for the fractional T3 lines.
- If you issue this command, be sure to issue the dsu mode and scramble commands. Otherwise, the interface might drop packets unexpectedly.
- The router offers a set of speeds in increments that depend on the DSU mode you specify. The actual speed of the fractional T3 lines will be the value closest to the fractional bandwidth you specify.
- Example
  host1(config-controll)#dsu bandwidth 10000
- Use the no version to clear the bandwidth.
- If you issue the no version, be sure to issue the no dsu mode and no scramble commands. Otherwise, the interface might drop packets unexpectedly.
- See dsu bandwidth.

dsu mode

- Use to set the DSU mode for the lines.
- Specify 0 for Digital Link mode or 2 for Larscom mode.
- If you issue this command, be sure to issue the dsu bandwidth and scramble commands. Otherwise, the interface might drop packets unexpectedly.
- Example
  host1(config-controll)#dsu mode 0
- Use the no version to clear the DSU mode.
- If you issue the no version, be sure to issue the no dsu bandwidth and no scramble commands. Otherwise, the interface might drop packets unexpectedly.
- See dsu mode.

scramble

- Use to enable cell scrambling on a T3 frame interface.
- If you issue this command, be sure to issue the dsu mode and dsu bandwidth commands. Otherwise, the interface might drop packets unexpectedly.
- Example
  host1(config-controll)#scramble
- Use the no version to turn off cell scrambling on the interface.
- If you issue the no version, be sure to issue the no dsu mode and no dsu bandwidth commands. Otherwise, the interface might drop packets unexpectedly.
- See scramble.

## Configuring an HDLC Channel

You must configure an HDLC channel for each T3 frame or E3 frame controller.

To configure an HDLC channel, configure a serial interface (for example, HDLC channel in slot 0, 1).

host1(config)#interface serial 0/1

### Optional Tasks

The following configuration tasks are optional when you configure an HDLC channel on a T3/E3 frame interface:

- Configure the cyclic redundancy check (CRC).
- Configure the HDLC idle character.
- Enable data inversion on the interface.
- Set the time interval for monitoring bit and packet rates.
- Set the maximum receive unit (MRU).
- Set the maximum transmit unit (MTU).
- Assign a text description or an alias to the serial interface.

crc

- Use to configure the size of the CRC.
- Specify the number of bits per frame (16 or 32) that are used to calculate the frame check sequence (FCS). Both the sender and receiver must use the same setting.
- The CRC is an error-checking technique that uses a calculated numeric value to detect errors in transmitted data.
- A 32-bit CRC should be used to protect longer streams at faster rates and, therefore, provide better ongoing error detection.
- Example
  host1(config-if)#crc 32
- Use the no version to restore the default value, 16.
- See crc.

idle-character

- Use to configure the HDLC idle character.
- The idle character is sent between HDLC packets.
- Specify one of the following idle characters:
  - flags—Sets the idle character to 0x7E
  - marks—Sets the idle character to 0xFF
- Example
  host1(config-if)#idle-character marks
- Use the no version to restore the default value, 0x7E (flags).
- See idle-character.

interface serial

- Use to configure a serial interface in the slot/port format.
  - slot—Number of the slot in which the line module resides in the chassis
  - port—Number of the port on the I/O module
- Example
  host1(config)#interface serial 3/0
- Use the no version to disable the interface.
- See interface serial.

invert data

- Use to enable data stream inversion for the interface.
- Enable data stream inversion only if it is turned on at the other end of the line.
- Example
  host1(config-if)#invert data
- Use the no version to disable the feature.
- See invert data.

load-interval

- Use to set the time interval at which the router calculates bit and packet rate counters.
- Choose a multiple of 30 seconds, in the range 30–300 seconds.
- Example
  host1(config-if)#load-interval 90
- Use the no version to restore the default value, 300 seconds.
- See load-interval.

mru

- Use to configure the MRU size for the interface.
- Specify a value in the range 4–9996 bytes.
- Coordinate this value with the network administrator on the other end of the line.
- If you set this parameter to a different value for another protocol, such as IP, the router uses the lower value. This could produce unexpected behavior in your network.
- Example
  host1(config-if)#mru 1500
- Use the no version to restore the default, 1600 bytes.
- See mru.

mtu

- Use to configure the MTU size for the interface.
- Specify a value in the range 4–9996 bytes.
- Coordinate this value with the network administrator on the other end of the line.
- If you set this parameter to a different value for another protocol, such as IP, the router uses the lower value. This could produce unexpected behavior in your network.
- Example
  host1(config-if)#mtu 1500
- Use the no version to restore the default, 1600 bytes.
- See mtu.

serial description

- Use to assign a text description or an alias to a serial HDLC interface.
- You can use this command to help you identify the interface and keep track of interface connections.
- The description or alias can be a maximum of 80 characters.
- Use the show interfaces serial command to display the text description.
- Example
  host1(config-if)#serial description boston09 hdlc channel
- Use the no version to remove the text description or alias.
- See serial description.