4-5
OC12 Packet Over SONET Line Card Installation and Configuration
OL-3437-01
Chapter 4 Configuring the OC12 POS Line Card
Configuring the Interfaces
Configuring Framing
The default framing setting is SONET. To configure for SDH, enter the pos framing-sdh command:
Router(config)#
interface
pos 3/1
Router(config-if)#
pos framing sdh
To change back to SONET, enter the no pos framing sdh command.
Setting the Source of the Transmit Clock
The clocking default specifies that the OC12 POS line card uses the recovered receive (RX) clock to
provide transmit (TX) clocking (called loop timing). To specify that the OC12 POS line card generates
the transmit clock internally, enter the clock source internal command:
Router(config)#
interface
pos 3/1
Router(config-if)#
clock source internal
To restore loop timing, enter the no clock source internal command or the clock source line command.
Configuring Cyclic Redundancy Checks
The cyclic redundancy check (CRC) default is for a 16-bit CRC. The CRC is an error-checking technique
that uses a calculated numeric value to detect errors in transmitted data. The OC12 POS line card also
supports a 32-bit CRC. The sender of a data frame calculates the frame check sequence (FCS). The
sender appends the FCS value to outgoing messages. The receiver recalculates the FCS and compares it
to the FCS from the sender. If a difference exists, the receiver assumes that a transmission error
occurred. To configure an interface for a 32-bit CRC, enter the crc 32 command:
Router(config)#
interface
pos 3/1
Router(config-if)#
crc 32
To disable the 32-bit CRC and return the interface to the default 16-bit CRC, enter the no crc 32.
Note
Both ends of the connection must be set to the same CRC mode.
Configuring SONET Payload Scrambling
SONET payload scrambling applies a self-synchronous scrambler (x^43+1) to the Synchronous Payload
Envelope (SPE) of the OC-12 interface to ensure sufficient bit-transition density. The default is for
SONET payload scrambling disabled.
Note
Both ends of the connection must use the same scrambling algorithm.
You enable SONET payload scrambling by using the pos scramble-atm command. (This command has
no keywords or arguments.)
To enable SONET payload scrambling, use the following command sequence:
Router(config)#
interface pos 3/1
Router(config-if)#
pos scramble-atm
Router(config-if)#
no shutdown
Router(config-if)#
end
