IBM3009K2672
IBM SONET/SDH Framer
Pointer Tracking Interpretation
The pointer tracking algorithm implemented in the SONET/SDH framer is illustrated in Pointer Tracking State
Machine on page 104. Refer to [G.783] and [GR-253] for definitions of the transitions. The pointer tracking
state machine is based on the pointer tracking state machine found in the ITU-T requirements, and is also
valid for both Bellcore and ANSI. The AIS to LOP transition of the state machine does not occur in Bellcore
mode (i.e., BELLCORE = 1).
Four pointer tracking state machines are employed, one for each AU-4/STS-3c. The pointer tracking uses the
H11 and H21 bytes. The pointer is extracted from the concatenation of the H1n and H2n bytes, and is inter-
preted as follows:
H1n Byte
H2n Byte
1
2
3
4
5
6
7
I
8
1
I
2
3
I
4
5
I
6
7
I
8
N
N
N
N
ss-bits
D
D
D
D
D
NNNN = New Data Flag Bits. This is interpreted as enabled = 1001 or 0001/1101/1011/1000, and normal or disabled
= 0110 or 1110/0010/0100/0111 (i.e., a single-bit error is tolerated).
ss = Size bits used in pointer tracking state machine interpretation if enabled by BELLCORE control bit being set to
’0’. When BELLCORE is set to ‘1’ these bits are ignored but, when it is set to ’0’, these bits are expected to
be 10.
I = Increment Bits defined as bit 7 of H1n and bits 1, 3, 5 and 7 of H2n.
D = Decrement Bits defined as bit 8 of H1n and bits 2, 4, 6 and 8 of H2n.
Negative Justification: Inverted 5 D-bits and accept majority rule. The 8 of 10 objective of O3-92 in [GR-253] can be
enabled by setting the JusITU bit in OR#Conf3 to ’0’.
Positive Justification: Inverted 5 I-bits and accept majority rule. The 8 of 10 objective of O3-92 in [GR-253] can be
enabled by setting the JusITU bit in OR#Conf3 to ’0’.
For STM-1/STS-3c operation, the pointer is a binary number with the range of 0 to 782 (decimal). It is a 10-bit
value derived from the two least significant bits of the H1 byte, with the H2 byte concatenated, to form an off-
set in 3-byte counts from the H3 byte location. For example, for an STM-1 signal, a pointer value of 0 indi-
cates that the VC-4 starts in the byte location 3 bytes after the H3 byte, whereas an offset of 87 indicates that
the VC-4 starts three bytes after the K2 byte.
In STM-4/STS-12 modes, there are four byte-interleaved AU-4s, so there are four H1/H2 byte pairs for deter-
mining the beginning (i.e., the J1 byte location) of their respective VC-4s. The operation of the four pointer
tracking state machines in this case is identical to that for 4 x STM-1/STS-3c operation.
When dealing with STS-12c/STM-4c, the pointer tracking state machine for macro 1 is used to locate the
beginning of the VC-4-4c. The pointer tracking uses the H11 and H21 bytes. The pointer is extracted from the
concatenation of the H11 and H21 bytes, and is interpreted as shown in the previous figure. However, the off-
set that is formed represents the number of 12-byte counts from the H3 byte location. For example, for an
STM-12c signal, a pointer value of 0 indicates that the VC-4 starts in the byte location twelve bytes after the
H3 byte, whereas an offset of 87 indicates that the VC-4 starts twelve bytes after the K2 byte. The concatena-
tion indication bytes are also examined in the corresponding macros (macros 2-4) and are monitored for LOP
and HPAIS per the state machine in Annex C of [G.783]. Concatenation Indication State Machine on page
105 illustrates the concatenation indicator state diagram. Refer to [G.783] for definitions of the transitions.
ssframer.01
8/27/99
Operation
Page 103 of 279
IBM [ IBM ]
