Verilink AS2000: The Basics (880-502981-001) Product Manual - Manual (Page 74)

Monitoring and Troubleshooting
5-8 Verilink Access System 2000: The Basics
When eight zeros are detected in the signal, an intentional bipolar
violation pattern is inserted on the transmit side and removed by
the receive side.
Loopbacks and Test Patterns
Loopbacks are an application module function, and are used to
determine which segment of the network is producing an alarm.
The loopbacks can be installed at the near end or far end of a point-
to-point connection.
Figure 5-2 illustrates which segment of the
point-to-point network is being tested when the near end has the
loopback. The following section describes the loopbacks. These
loopbacks are applicable to T1 and E1 equipment. T3 loopbacks are
defined in the HDM manuals.
NOTE: All five of the following loopbacks activate the LED indicators
on the front panel of an NCC, SCC, DCSU, DIDCSU, and TAC.
The affected port indicator illuminates amber during the
loopback.
A test pattern is a known sequence of bits sent continuously
toward another point in the network. Test patterns are used with
loopbacks to stress the network, and to see if the same pattern is
returned without errors.
Figure 5-2 Near End Loopbacks
Framer DTE DTE
DTE DTE
DTE DTE
DTE DTE
Framer
Framer
Level 1
Equip
All ones keep-alive
Data dropped at arrow
Framer
Framer
Framer
Level 1
Equip
Framer
Framer
Framer
Framer
Line
Loopback
Payload
Loopback
Equipment
Loopback
Data Port
Loopback
Near End Far End
Repeater
Loopback