Configuring The Clock Source - Cisco 7304 Installation And Configuration Manual

Chapter 4 Configuring the 6E3 Line Card
Table 4-6
Purpose
Enable 32-bit CRC
Return to default 16-bit
CRC
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 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 sender appends the FCS value
to the message. The receiver recalculates the FCS and compares its calculation to the FCS from the
sender. When the CRC on a received frame is not correct, the frame is dropped. The card does not send
a request to the remote end to transmit the frame. (A higher layer protocol is required to implement the
retransmission.)
Enable 32-bit CRC using the crc 32 command. Before you can enable 32-bit CRC, you must use the
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 systems in which the 6E3 line card is supported.
Use the no crc 32 command to disable the 32-bit CRC setting and return the interface to the default
16-bit CRC setting.
When you have finished, press Ctrl-Z—hold down the Control key while you press Z—or enter end or
exit to exit configuration mode and return to the EXEC command interpreter prompt. Then write the new
configuration to NVRAM using the copy running-config startup-config command.
When enabling a 16-bit or 32-bit CRC on a local interface, ensure that the remote device is also
Note
configured for a 16-bit or 32-bit CRC.
For command descriptions, refer to the Configuration Fundamentals Configuration Guide publication.
For more information, see the
and the

Configuring the Clock Source

The only exception for matching local and remote E3 port configurations is that the clock sources must
be set opposite each other. Therefore, if you enter the clock source internal command for the local E3
port, you must enter clock source line for the remote E3 port.
OL-5061-01
CRC Commands
Command
crc size
no crc size
"Obtaining Additional Publications and Information" section on page xi
"Obtaining Additional Publications and Information" section on page
Cisco 7304 6-Port Clear Channel E3 Line Card Installation and Configuration
Example
The example enables 32-bit CRC on a serial interface:
Router(config)# interface serial 3/0
Router(config-if)# crc 32
The example disables 32-bit CRC on a serial interface and
returns to the default 16-bit CRC:
Router(config)# interface serial 3/0
Router(config-if)# no crc 32
Configuring the Interfaces
xi.
4-7