XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
PRELIMINARY
REV. P1.0.1
384
The first byte of this 16-byte string is a frame start
marker and is typically of the form [1, C6, C5, C4, C3,
C2, C1, C0]. The “1” in the MSB (most significant bit)
of this first byte is used to identify this byte as the
frame start marker (e.g., the first byte of the 16-byte
Trail Trace Buffer Sequence). The bits: C6 through
C0 are the results of a CRC-7 calculation over the
previous 16-byte frame. The subsequent 15 bytes
are used for the transport of 15 ASCII characters re-
quired for the E.164 numbering format.
6.1.1.4
The MA byte is responsible for carrying the FERF
(Far-End Receive Failure) and the FEBE (Far-End
Block Error) status indicators from one terminal to an-
other. The MA byte-field also carries the Payload
Type, the Payload Dependent and the Timing Marker
indicators. The byte format for the MA byte is pre-
sented below.
Maintenance and Adaptation (MA) Byte
Bit 7 - FERF (Far-End Receive Failure)
If the Receive E3 Framer block (at a Local Terminal)
is experiencing problems receiving E3 frame data
from a Remote Terminal (e.g., an LOS, OOF or AIS
condition), then it will inform the Remote Terminal
Equipment of this fact by commanding the Local
Transmit E3 Framer block to set the FERF bit-field
(within the MA byte) of an Outbound E3 frame, to “1”.
The Local Transmit E3 Framer block will continue to
set the FERF bit-field (within the subsequent Out-
bound E3 frames) to “1” until the Receive E3 Framer
block no longer experiences problems in receiving
the E3 frame data. If the Remote Terminal Equip-
ment receives a certain number of consecutive E3
frames, with the FERF bit-field set to “1”, then the Re-
mote Terminal Equipment will interpret this signaling
as an indication of a Far-End Receive Failure (e.g., a
problem with the Local Terminal Equipment).
Conversely, if the Receive E3 Framer block (at a Lo-
cal Terminal Equipment) is not experiencing any
problems receiving E3 frame data from a Remote
Terminal Equipment, then it will also inform the Re-
mote Terminal Equipment of this fact by commanding
the Local Transmit E3 Framer block to set the FERF
bit-field (within the MA byte-field) of an Outbound E3
frame (which is destined for the Remote Terminal) to
“0”. The Remote Terminal Equipment will interpret
this form of signaling as an indication of a normal op-
eration.
N
OTE
:
A detailed discussion into the practical use of the
FERF bit-field is presented in Section 5.2.4.2.
Bit 6 - FEBE (Far-End Block Error)
If a Local Receive E3 Framer block detects an error
in the EM byte, within an incoming E3 frame that it
has received from the Remote Terminal Equipment,
then it will inform the Remote Terminal Equipment of
this error by commanding the Local Transmit E3
Framer block to set the FEBE bit-field (within the MA
byte-field) of an Outbound E3 frame (which is des-
tined for the Remote Terminal Equipment) to “1”. The
Remote Terminal Equipment will interpret this signal-
ing as an indication that the E3 frames that it is trans-
mitting back out to the Local Receive E3 Framer
block are erred.
Conversely, if the Local Receive E3 Framer block
does not detect any errors in the EM byte, within the
incoming E3 frame, then it will also inform the Re-
mote Terminal Equipment of this fact by commanding
the Local Transmit E3 Framer block to set the FEBE
bit-field of an Outbound E3 frame (which is destined
for the Remote Terminal Equipment) to “0”.
N
OTE
:
A detailed discussion into the practical use of the
FEBE bit-field is presented in Section 5.2.4.2.
Bits 5 - 3 Payload Type
These bit-fields indicates to the Remote Terminal
Equipment, what kind of data is being transported in
the 530 bytes of E3 frame payload data. Some of the
defined payload type values are tabulated in
Table 85 .
THE MAINTENANCE AND ADAPTATION (MA) BYTE FORMAT
B
IT
7
B
IT
6
B
IT
5
B
IT
4
B
IT
3
B
IT
2
B
IT
1
B
IT
0
FERF
FEBE
Payload Type
Payload Dependent
Timing Marker