S/UNI®-JET Data Sheet
Released
13.5 G.751 E3 Frame Format
The S/UNI-JET provides support for the G.751 E3 frame format, shown in Figure 13. This format
can be extended to allow for direct byte mapping or PLCP mapping of ATM cells.
Figure 13 G.751 E3 Frame Structure
1
1
1
1
0
1
0
0
0
0
RAI Na
372 Payload bits
380 Payload bits
380 Payload bits
376 Payload bits
C
C
C
C
C
C
11 21 31 41
C
C
C
12 22 32 42
C
C
C
J
J
J
J
4
13 23 33 43
1
2
3
The processing of the overhead bits in the G.751 E3 frame is described in Table 39. In the
transmit direction, the overhead bits can be inserted on a bit-by-bit basis from a user supplied data
stream using the TOH, TOHINS, TOHFP, and TOHCLK signals. In the receive direction, most of
the overhead bits are brought out serially on the ROH data stream.
When used to transport ATM cells in either ATM direct mapping mode or with PLCP framing,
bits 13, 14, 15, and 16 of the E3 frame (directly following the RAI and Na bits) are set to 1, 1, 0
and 0.
Table 39 G.751 E3 Frame Overhead Operation
Control Bit
Transmit Operation
Receive Operation
Frame Alignment
Inserts the frame alignment
Finds frame alignment by searching for the
frame alignment signal. When the pattern has
been detected for three consecutive frames,
an in-frame condition is declared. When errors
are detected in four consecutive frames, an
OOF condition is declared.
Signal
signal 1111010000b.
RAI:
RAI
Optionally asserts the RAI
signal under a register
control or when LOS, OOF,
AIS and LCD conditions are
detected.
Extracts the RAI signal and outputs it on the
ROH output pin. The state of the RAI signal is
also written to a register bit.
Na:
Asserts the National Use bit
under a register control or
from the internal HDLC
controller.
Extracts the National Use bit and stores the
value in a register bit.
National Use Bit
Cjk:
When the device is
Extracts the Justification Service Bits on the
ROH output pin when the Cjk bits are
configured as overhead.
configured as an E3 G.751
framer device, the
Justification Service
Bits
Justification Service Bits can
be inserted on the TDATI
input pin the same way as
normal payload data.
When the device is
configured for ATM
application, the Justification
Service Bits are used as
payload bits.
Proprietary and Confidential to PMC-Sierra, Inc., and for its Customers’ Internal Use
Document ID: PMC-1990267, Issue 3
269
PMC [ PMC-SIERRA, INC ]
