XRT74L73 Datasheet, PDF (382/488 Pages) Exar Corporation – 3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER

XRT74L73
3 CHANNEL, ATM UNI/PPP DS3/E3 FRAMING CONTROLLER
REV. P1.0.1
PRELIMINARY
FRAMER OPERATING MODE REGISTER (ADDRESS = 0X00)
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT2
BIT 1
BIT 0
Local Loopback DS3/E3*
Internal LOS
Enable
RESET
Interrupt Frame Format
Enable Reset
TimRefSel[1:0]
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
x
1
x
0
x
x
x
x
6.1.1.1 Frame Alignment (FA1 and FA2) Bytes
FA1 and FA2 are known as the frame alignment
bytes. The Receive E3 Framer, while trying to ac-
quire or maintain framing synchronization with its in-
coming E3 frames, will attempt to locate these two
bytes. FA1 is assigned the value “0xF6” and FA2 is
assigned the value “0x28”.
6.1.1.2 Error Monitor (EM) Byte
The EM byte contains the results of BIP-8 (Bit-Inter-
leaved Parity) calculations over an entire E3 frame.
The Bit Interleaved Parity (BIP-8) byte field supports
error detection, during the transmission of E3 frames,
between the Local Terminal Equipment and the Re-
mote Terminal Equipment.
The Transmit E3 Framer will compute the BIP-8 value
over the 537 octet structure, within each E3 frame.
The resulting BIP-8 value is then inserted into the EM
byte-field within the very next E3 frame. BIP-8 is an
eight bit code in which the nth bit of the BIP-8 code
reflects the even-parity bit calculated with the nth bit
of each of the 537 octets within the E3 frame. Thus,
the BIP-8 value presents the results for 8 separate
even-bit parity calculations.
The Receive E3 Framer will compute its own version
of the EM bytes for each E3 frame that it receives.
Afterwards, it will compare the value of its locally
computed EM byte with the EM byte that it receives in
the very next E3 frame. If the two EM byte values are
equal, then the Receive E3 Framer will conclude that
this E3 frame was received in an error-free manner.
Further, the Receive E3 Framer will block will inform
the Remote Terminal Equipment of this fact by having
the Local Terminal Equipment set the FEBE (Far-
End-Block Error) bit, within the MA Byte of an Out-
bound E3 frame (to the Remote Terminal Equipment)
to “0”. Please see Section 5.1.1 for a discussion of
the MA Byte.
However, if the Receive E3 Framer block detects an
error in the incoming EM byte, then it will conclude
that the corresponding E3 frame is errored. Further,
the Receive E3 Framer block will inform the Remote
Terminal (e.g., the source of this erred E3 frame) of
this fact by having the Local Terminal Equipment
(e.g., the Transmit E3 Framer block) set the FEBE bit,
within an Outbound E3 frame (destined to the Re-
mote Terminal) to “1”.
NOTE: A detailed discussion on the practical use of the EM
byte is presented in Section 5.2.2.
6.1.1.3 The Trail-Trace Buffer (TTB) Byte
This byte-field is used to repetitively transmit a Trail-
access point identifier so that a trail receiving terminal
can verify its continued connection to the intended
transmitter. The trail access point identifier uses the
16-byte numbering format as tabulated in Table 84 .
TABLE 84: DEFINITION OF THE TRAIL TRACE BUFFER BYTES, WITHIN THE E3, ITU-T G.832 FRAMING FORMAT
TRAIL TRACE BITS
BYTE NUMBER
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
1 (Frame Start
1
Marker)
C6
C5
C4
C3
C2
C1
C0
2
X
X
X
X
X
X
X
X
*
X
X
X
X
X
X
X
X
*
X
X
X
X
X
X
X
X
16
X
X
X
X
X
X
X
X
383