Optional Tasks

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

• Configure the CRC.
• Configure the HDLC idle character.
• Enable data inversion on the interface.
• Set the MRU.
• Set the 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 (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, 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-ifs)#idle-character marks

• Use the no version to restore the default value, 0x7E (flags).
• See idle-character.

interface serial

• Use to specify a serial interface.
• Example for unframed E1 interface

  host1(config)#interface serial 4/0:1/1/1/1/1

• Example for fractional T1/E1 interface

  host1(config)#interface serial 4/0:1/1/1/1/1

• Example for unchannelized T3 interface

  host1(config)#interface serial 4/0:1/1

• Example for T3 interface channelized to fractional T1

  host1(config)#interface serial 4/0:1/1/10/22

• Use the no version to remove 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.

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 value with a different value for another protocol, such as IP, the router uses the lower value. The lower MRU might cause unexpected results in the 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.
• You should coordinate this value with the network administrator on the other end of the line.
• You can set a different MTU value in higher-level protocols, such as IP. If you do, the router uses the lower value. The lower MTU might cause unexpected results in the 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 show interfaces serial to display the text description.
• Example

  host1(config-if)#serial description ottawa012 hdlc channel

• Use the no version to remove the text description or alias.
• See serial description.

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