XRT72L50 Datasheet, PDF (354/471 Pages) Exar Corporation – SINGLE CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER

XRT72L50
SINGLE CHANNEL DS3/E3 FRAMER WITH HDLC CONTROLLER
REV. 1.2.1
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TABLE 65: DEFINITION OF THE TRAIL TRACE BUFFER BYTES, WITHIN THE E3, ITU-T G.832 FRAMING FORMAT
BYTE NUMBER
1 (Frame Start
Marker)
2
*
*
16
BIT 7
1
X
X
X
X
BIT 6
C6
X
X
X
X
BIT 5
C5
X
X
X
X
TRAIL TRACE BITS
BIT 4
BIT 3
C4
C3
X
X
X
X
X
X
X
X
BIT 2
C2
X
X
X
X
BIT 1
C1
X
X
X
X
BIT 0
C0
X
X
X
X
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 required for the E.164 numbering format.
The MSB (bit 7) of these bytes is always “0”.
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 another. 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 presented below.
The Maintenance and Adaptation (ma) byte format
BIT 7
FERF
BIT 6
FEBE
BIT 5
BIT 4
Payload Type
BIT 3
BIT 2
BIT 1
Payload Dependent
BIT 0
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 Outbound 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 receives 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 problem with the Local Terminal Equipment).
Conversely, if the Receive E3 Framer block (at a Local Terminal Equipment) is not experiencing any problems
receiving E3 frame data from a Remote Terminal 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 operation.
NOTE: A detailed discussion into the practical use of the FERF bit-field is presented in Section 6.2.4.2.1.
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
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