XRT72L52 Datasheet, PDF (365/480 Pages) Exar Corporation – TWO CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

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PRELIMINARY
XRT72L52
TWO CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
REV. P1.1.3
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 Maintenance and Adaptation (MA) Byte
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.
THE MAINTENANCE AND ADAPTATION (MA) BYTE FORMAT
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
FERF
FEBE
Payload Type
Payload Dependent
Timing Marker
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 Equipment re-
ceives a certain number of consecutive E3 frames,
with the FERF bit-field set to “1”, then the Remote
Terminal Equipment will interpret this signaling as an
indication of a Far-End Receive Failure (e.g., a prob-
lem 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 Ter-
minal Equipment, then it will also 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-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.
NOTE: 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 destined for
the Remote Terminal Equipment) to “1”. The Remote
Terminal Equipment will interpret this signaling as an
indication that the E3 frames that it is transmitting
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”.
NOTE: 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 70.
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