Cisco 7300-6T3 Especificações descarregar pdf (Página 41)

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Cisco 7304 6-Port Clear Channel E3 Line Card Installation and Configuration

OL-5061-01

Chapter 4 Configuring the 6E3 Line Card

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 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.

Note When enabling a 16-bit or 32-bit CRC on a local interface, ensure that the remote device is also

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 “Obtaining Additional Publications and Information” section on page xi

and the “Obtaining Additional Publications and Information” section on page xi.

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.

Table 4-6 CRC Commands

Purpose Command Example

Enable 32-bit CRC crc size The example enables 32-bit CRC 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 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

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