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24 Patch Release Note
Patch 86241-05 for Software Release 2.4.1
C613-10340-00 REV E
The three C-bits in M-subframe 4 are designated as FEBE bits. The FEBE bits
are returned to the far end to indicate the occurrence of a framing error or CP-
bit parity error. If none occur, the FEBE bits are set to all ones. One or all of the
FEBE bits are set to zero if a CP-bit parity error or an error in the F or M bits is
found.
The three C-bits in M-subframe 5 are assigned as a 28.2kbits/s terminal-to-
terminal-path maintenance data link. This data link can be switched off at the
command interface, If it is switched off, the C-bits in M-subframe 5 are set to all
ones. If switched on, the maintenance channel can convey the following
information:
■ Path Identification Signal.
A set of ASCII text strings that can be used to uniquely identify this
particular DS3 path. This can be useful if the DS3 signal is, at some point in
its path, multiplexed into a higher order signal such as DS4 or OC-3. It is
common for lower-order signals to be switched within a cross-connect. If
this happens it is possible that the wrong DS3 signal is switched through to
the switch. When this happens the overhead bits are all correct, so there is
no indication that the wrong signal has been applied. The Path
Identification Signal can be agreed by the two parties at either end of the
network and tested to ensure that it is the right DS3 signal that has been
received.
■ Idle Signal.
A set of ASCII text strings that can be used to provide the location of the
source of an idle signal.
■ Test Signal.
A set of ASCII text strings that can be used to provide the location of the
source of a test signal.
These signals are sent once every second. All other C-bits are for future use.
Loopbacks
The DS3 interface provides four types of loopback; line, payload, diagnostic,
and remote. These loopbacks are activated by the ENABLE DS3 TEST
command.
Line loopback is shown in Figure 2 on page 24. In this loopback mode the
receive signal is looped straight to the transmit signal.
Figure 2: Line Loopback.
Payload loopback is similar to line loopback. The difference is that only the
payload load is looped back from receive to transmit. The overhead is sourced
from the DS3 NSM.
Far End
RX
TX
TX
RX
DS3 NSM
DS32