Datasheet

DS3112
132 of 133
14.12 G.747 Framing Structure and E12 Multiplexing
The G.747 frame structure is made up of five 168-bit sets (Figure 14-9). The five sets are transmitted one
after another (...Set1/Set2/Set3/Set4/Set5/Set1...) to make up the complete G.747 frame structure. The
Frame Alignment Signal (FAS) is placed in the first 9 bits of Set 1. Set 2 contains the Remote Alarm
Indication (RAI) bit and a Parity Bit (PAR) as well as a reserved bit, which is fixed to a one. The PAR bit
will be set to a one when there are odd numbers of ones from the tributaries in the preceding frame and it
will be set to a zero when there is an even number of ones. The parity calculation does not include the
FAS, RAI, reserved bit, or Justification Control Bits. The three tributaries are bit interleaved starting with
a bit from Tributary 1 immediately after the FAS in Set 1. The first three bits of Sets 3, 4, and 5 are the
Justification Control Bits. Bits 4 to 6 of Set 5 are the Stuffing Bits. The Justification Control bits control
when data will be stuffed into the Stuffing Bit positions. When a majority of the three Justification
Control Bits from a particular tributary is set to zero, the Stuffing Bit position will be used for tributary
data. When the Justification Control Bits are majority decoded to be one, the Stuffing Bit will not be used
for tributary data.
Figure 14-9. G.747 Frame Structure
Set 1
Bit 1 Bit 168
FAS (111010000) b
11
b
21
b
31
b
12
b
22
b
32
b
13
...bits from the tributaries...
Set 2
Bit 1 Bit 168
RAI PAR 1 ...bits from the tributaries...
Set 3
Bit 1 Bit 168
c
11
c
21
c
31
...bits from the tributaries...
Set 4
Bit 1 Bit 168
c
12
c
22
c
32
...bits from the tributaries...
Set 5
Bit 1 Bit 168
c
13
c
23
c
33
s
1
s
2
s
3
...bits from the tributaries...
NOTE 1: BIT 1 OF SET 1 IS TRANSMITTED FIRST.
NOTE 2: BJI TRIBUTARY BITS J = TRIBUTARY NUMBER I = BIT NUMBER
NOTE 3: CJI JUSTIFICATION CONTROL BITS J = TRIBUTARY NUMBER I = CONTROL STUFFING BIT NUMBER
NOTE 4: SJ STUFFING BITS J = TRIBUTARY NUMBER