Configuring Half-Duplex and Binary Synchronous Communications
Configuring CRCs
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.
To enable 32-bit CRC on an interface, specify the slot and port address of the interface followed by the command crc 32. In the example that follows, the first serial port on a PA-4T+ in port adapter slot 1 of a Cisco 7200 series, Cisco uBR7200 series, or Cisco 7100 series router is configured for
32-bit CRC:
Router# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)# interface serial 1/0
Router(config-if)# crc 32
Ctrl-Z
Router#
In the example that follows, the first serial port on a PA-4T+ on a VIP2 in interface processor slot 3 is configured for 32-bit CRC:
Router# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)# interface serial 3/1/0
Router(config-if)# crc 32
Ctrl-Z
Router#
To disable CRC-32 and return to the default CRC-16 (CRC-CITT) setting, specify the slot and port address and use the no crc 32 command. For command descriptions, refer to the Configuration Fundamentals Configuration Guide publication. If you need more information, see the “Cisco Connection Online” section on page vii and the “Related Documentation” section on page vi.
If you are configuring a PA-4T+ installed on the Cisco 7200 series router, proceed to the following section “Configuring Half-Duplex and Binary Synchronous Communications,” otherwise, proceed to the “Checking the Configuration” section on page 8-14.
Configuring Half-Duplex and Binary Synchronous Communications
This section explains how to configure PA-4T+ interfaces for half-duplex and Bisync operation in Cisco 7100 series and Cisco 7200 series routers.
Note Cisco IOS Release 11.2(7a)P or later supports half-duplex and bisync operation on PA-4T+ port adapters in Cisco 7200 series router.
Cisco IOS Release 12.0(3)T or later, or 12.0(1)XE or later support nonstandard clock rates on
PA-4T+ interfaces installed in Cisco 7204VXR and Cisco 7206VXR routers.
