4-10
PA-E3 Serial Port Adapter Installation and Configuration
OL-3502-04
Chapter 4 Configuring the PA-E3
Configuring the Interfaces
Step 8
Write the new configuration to NVRAM as follows:
Router#
copy running-config startup-config
[OK]
Router#
This completes the procedure for creating a basic configuration.
The PA-E3 supports internal or external clocking, and the clock rate is fixed at 32,064 kbit/s per ITU
G.703 and cannot be changed.
Configuring Cyclic Redundancy Checks
Cyclic redundancy check (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 sender appends the FCS value to the message. The receiver recalculates the FCS and compares
its calculation to the FCS 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. 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 PA-E3 is supported.
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-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.
For command descriptions, refer to the Configuration Fundamentals Configuration Guide on Cisco.com.
For more information, see the
“Related Documentation” section on page viii
.
Table 4-4
CRC Commands
Purpose
Command
Example
Enable 32-bit CRC.
crc size
The example enables 32-bit CRD on a serial interface:
Router(config)#
interface serial 3/0
Router(config-if)#
crc 32
Return to default
16-bit CRC.
no crc size
The example disables 32-bit CRD on a serial interface and returns to the default
16-bit CRC:
Router(config)#
interface serial 3/0
Router(config-if)#
no
crc 32
