Specifying T3 Framing
Note The local port configuration must match the remote port configuration. For example, if you enable scrambling on the local port, you must do the same on the remote port.
See the “Interoperability Guidelines for PA-T3 Serial Port Adapter DSUs” section on page 2-5 for information regarding DSU feature compatibilities.
Specifying T3 Framing
In interface configuration mode, specify T3 framing by entering the framing {c-bit m13 bypass} configuration subcommand, as in the following example:
router(config-if)# framing c-bit
Use the no form of this command to return to the default, which is C-bit framing.
Note If you use the bypass option, scrambling must be set to the default, disabled; the DSU mode must be set to the default, 0; and the DSU bandwidth must be set to the default, 44210.
Setting the Cable Length
In interface configuration mode, set the cable length (range of 0 to 450 feet), as in the following example:
router(config-if)# cablelength 250
Use the no form of this command to return to the default, which is 10 feet.
Configuring Cyclic Redundancy Checks
The PA-T3 serial port adapter uses a 16-bit CRC by default; it also supports a 32-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 sending 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.
Note To enable 32-bit CRC on an interface, follow Steps 1 and 2 of the preceding procedure (enter configuration mode and specify the slot and port address [and the interface port number for a VIP2] of the PA-T3 serial port adapter), and then enter the command crc 32. Enter Ctrl-Zto exit from configuration mode.
