4-8
Clear Channel 6-Port T3 (DS3) Line Card Installation and Configuration
OL-3449-02
Chapter4 Configuring the 6T3 Line C ard
Configuring the Interfaces
CRC is an error-checking technique that uses a calculated numeric value to detect errors in transmitted
data. All interfaces use a 16-bit CRC (CRC-CITT) by default but also support a 32-bit CRC. The sender
of a data frame calculates the frame check sequence (FCS). Before it sends a frame, the sen der app end s
the FCS value to the message. The receiver reca lculates the FCS and co mpares i ts calculati on to the FC S
from the sender. If there is a difference between the two calculations, the receiver assumes that a
transmission error occurred and sends a request to the sender to resend the frame.
Enable 32-bit CRC using the crc 32 command. Befo re you can en able 32-b it CRC , you must use th e
interface serial command (followed by the interface address of the interface) to select the interface on
which you want to enable 32-bit CRC. This command functions in the same way on all supported
platforms.
In the example that follows, 32-bit CRC is specified:
Router(config-if)# crc 32
The preceding command example applies to all sys tems in wh ich the 6T3 lin e card is supporte d.
Use the no crc 32 command to disable CRC-32 and return the interface to the default CRC-16
(CRC-CITT) setting.
When you have finished, press Ctrl-Zhold down the Control key while you press Zor enter end or
exit to exit configuration mode and return to the EXEC command interpreter pr ompt. Then write t he new
configuration to NVRAM using the copy running-config startup-config command.
Note When enabling a 16-bit or 32-bit CRC on a local interface, ensure tha t the re mote d evice
is also configured for a 16-bit or 32-bit CRC.
For command descriptions, refer to the Configuration Fundamentals Configuration Guid e pub licat ion.
For more information, see the Obtaining Documentation section on pageviii and the Obtaining
Technical Assistance section on pagex.
Configuring the Clock Source
The only exception for matching local and remote DS3 port configurations is that the cloc k sources must
be set opposite each other. Therefore, if you enter the clock source internal command for the local DS3
port, you must enter clock source line for the remote DS3 port.
Defining the DSU Mode
In interface configuration mode, define the DSU interoperability mode by entering the
dsu mode [adtran |[cisco |digital-link | kentrox| larscom ] configuration subcommand, as in the
following example:
Router(config-if)# dsu mode cisco
Use the no form of this command to return to the default, 0.
Note The local port configuration must match the remote port configuration. For exampl e, if you define the
DSU interoperability mode as cisco on the local port, you must do the same on the remote port. You need
to know what type of DSU is at the remote port to find out if it interoperates with the 6T3line card. For
T3 serial interfaces, specify cisco for connect ion from a 6T3 line card to another 6T3line card. Specify