Datasheet

Installing 2T16S Network Processor Modules in the Cisco 4000 Series

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Calculating CRCs on Cisco 4000 Series Serial Interfaces

All Cisco 4000 series router serial interfaces support CRC-CCITT, a 16-bit CRC. CRC is an

error-checking technique that uses a calculated numeric value to detect errors in transmitted data. The

sender of a data frame divides the bits in the frame message by a predetermined number to calculate a

remainder or frame check sequence (FCS). Before it sends the frame, the sender appends the FCS value

to the message so that the frame contents are exactly divisible by the predetermined number. The receiver

divides the frame contents by the same predetermined number that the sender used to calculate the FCS.

If the result is not 0, the receiver assumes that a transmission error occurred and sends a request to the

sender to resend the frame.

The designator 16 indicates the number of check digits per frame that are used to calculate the FCS.

CRC-16, which transmits streams of 8-bit characters, generates a 16-bit FCS. Both the sender and the

receiver must use the same setting of 16. The default for all serial interfaces is for 16-bit CRC.

Note Refer to the Configuration Fundamentals Configuration Guide and the Configuration Fundamentals

Command Reference publications for more software configuration information. These documents are

available on the Documentation CD or the Web.

Checking the Router Configuration

When you have configured the interface, use the show interface command to check the network

interface statistics. Options to the show interface command include the type of interface (for example,

serial), and the unit number of the interface. The following example shows the use of the show interface

command:

router# show interface serial 0

The field underrun in the output of the show interface command may be nonzero in approximately 1 of

250,000 packets.

To display the current internal status of an interface module, use the show controller command with the

interface type and unit number options:

router# show controller serial 0

Problem Solving

Use the information in this section to help isolate problems. This section helps you rule out the router as

the problem source. Whether or not you can locate the source of your problem, you can contact a service

representative for information on how to proceed in resolving the problem. See the section “Cisco

Connection Online” on page 46. Before you call, have the following information ready:

• Chassis type and serial number

• The type of network processor module and serial number

• Maintenance agreement or warranty information

• Type of software and version number

• Date you received the new chassis and network processor module

• Brief description of your problem

• Brief explanation of steps you took to isolate the problem