7705 SAR Interfaces
470
Interface Configuration Guide
3HE 11011 AAAC TQZZA Edition: 01
loopback (DS1)
Syntax loopback {line | internal | fdl-ansi | fdl-bellcore | payload-ansi}
no loopback
Context config>port>tdm>ds1
Description This command puts the specified port or channel in a loopback mode.
A line loopback loops frames received on the corresponding port or channel back towards
the transmit (egress) direction before reaching the framer. The bit stream is not reframed. The
electrical signal is regenerated by the Tx line interface unit (LIU) and the timing is provided
by the Rx LIU.
An internal loopback loops the frames that are coming in an egress direction from the fabric
towards the framer, back to the fabric. This is usually referred to as an equipment loopback.
The Tx signal is looped back and received by the interface.
The fdl-ansi loopback command sends a repeating 16-bit ESF data link code word to the
remote end requesting that it enter into a network line loopback. The ansi keyword enables
the remote line FDL ANSI bit loopback on the T1 line, in accordance with the ANSI T1.403
specification.
The fdl-bellcore loopback command sends a repeating 16-bit ESF data link code word to the
remote end requesting that it enter into a network line loopback. The bellcore keyword
enables the remote line FDL Bellcore bit loopback on the T1 line, in accordance with the
Bellcore TR-TSY-000312 specification.
The payload-ansi loopback command sends a repeating 16-bit ESF data link code word to
the remote end requesting that it enter into a network payload loopback. A payload loopback
loops frames back towards the transmit (egress) direction after reaching the framer. The bit
stream is reframed. The electrical signal is regenerated by the Tx LIU and the timing is
provided by the Rx LIU.
The loopback command is not saved to the system configuration.
The no form of this command disables the specified type of loopback.
Default no loopback
Note:
• The fdl-ansi, fdl-bellcore and payload-ansi options can only be configured if DS1
framing is set to ESF.
• The 4-port OC3/STM1 / 1-port OC12/STM4 Adapter card cannot initiate fdl-ansi, fdl-
bellcore, or payload-ansi loopbacks.
• The 4-port OC3/STM1 / 1-port OC12/STM4 Adapter card supports up to 16 line
loopbacks and 16 internal loopbacks at a time.
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