Configuring NRZI Format
All EIA/TIA-232 interfaces on the 4-Port Serial Interface SPA support non-return-to-zero (NRZ) and
non-return-to-zero inverted (NRZI) formats. Both formats use two different voltage levels for transmission.
NRZ signals maintain constant voltage levels with no signal transitions
—
no return to a zero voltage
level
—
during a bit interval and are decoded using absolute values: 0 and 1. NRZI uses the same constant
signal levels but interprets the absence of data
—
a space
—
at the beginning of a bit interval as a signal transition
and the presence of data
—
a mark
—
as no signal transition. NRZI uses relational encoding to interpret signals
rather than determining absolute values.
Use the following commands when configuring NRZI format:
Purpose
Command
Enters global configuration mode.
Router#
configure terminal
Selects the interface to configure and enters interface
configuration mode.
Router(config)#
interface serial slot/subslot/port
Enables NRZI encoding.
Router(config-if)#
nrzi-encoding
Disables NRZI encoding.
Router(config-if)#
no nrzi-encoding
Configuring Cyclic Redundancy Checks
Cyclic redundancy checking (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 designators 16 and 32 indicate the length (in bits) of the frame check sequence (FCS). 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 set the length of the cyclic redundancy checks (CRC), use the following commands:
Purpose
Command
Enters global configuration mode.
Router#
configure terminal
Selects the interface to configure and enters interface
configuration mode.
Router(config)#
interface serial slot/subslot/port
Specifies the length of the CRC, where:
•
16
—
Specifies a 16-bit length CRC. This is the
default.
•
32
—
Specifies a 32-bit length CRC.
To set the CRC length to the default value, use the
no form of this command.
Router(config-if)#
crc
{
16
|
32
}
Cisco ASR 1000 Series Aggregation Services Routers SIP and SPA Software Configuration Guide, Cisco IOS XE
Everest 16.5
OL-14127-17
285
Configuring the 4-Port Serial Interface SPA
Optional Configurations