POINTER IN SDH

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TX-I FACULTYALTTC,GZB

AU-4 POINTER

•Pointer at AU provides “Dynamic alignment” of VC-n with in the AU-n frame ,VC-n is allowed to “Float” with in the AU-n.•Pointer is able to accommodate differences in•Phases of the VC-n and SOH•In frame rates (frequencies) also

AU-4 POINTER LOCATION

•AU-4 pointer is contained in the H1,H2,H3 bytes of the 4th row of SOH.

•The 3 individual AU-3 pointer are contained in three separate sets of H1,H2 &H3 bytes

1 2 3 4 5 6 7 8 9 10

123456789123456789

AUG 270

H1 Y Y H2 1* 1* H3 H3 H3 0 - - 1 - 86 - -

Negative Justification opportunoity (3 byte)Positive justification opportunity (3 byte)

125µs

250µs

521

522

7820 86H1 Y Y H2 1* 1* H3 H3 H3

AU-4 POINTER OFFSET NUMBERING.

AU4 POINTER VALUE

•Pointer value contained in the H1 andH2 byte designate the location of byte where VC-4 begins.•The two byte allocated to the pointer function can be viewed as one word.•The last ten bits of the pointer (7-16) of the pointer carry the pointer value.•H3 byte is used for negative Justification which may then is filled with data

N N N N S S I D

THREE NEGATIVE JUSTIFICATION BYTE

I D I D I D I D

New Data Flag unspecified

10 bit pointer value

POINTER BITSHI

H2

3*H3

•I Increment,•D Decrement,•N New Data Flag .•Negative Justification- Invert 5 D- Bits- Accept Majority Vote Decision•Positive Justification - Invert 5 I- Bits- Accept Majority Vote Decision

PARAMETER MEANINGNDF=Enabled when 3 out of 4 bits matches

with 1001

=Disabled when 3 out of 4 bits matches with 0110

=Invalid for other codes Purpose= To change the value of

pointer arbitrarily

BITS 7 TO 16

ACTUAL POINTER RESIDES HERE

•The AU-4 pointer value is binary number with a range of 0 to 782 which indicates the offset, in three bytes increments,between the pointer and the first byte of VC-4.

Frequency Justification•If there is frequency offset between the framerate of AU4 and that of the VC_4, than the pointervalue will be incremented or decremented as needed.

•This should be accompanied by a corresponding positive or negative justification byte or bytes.

•Consecutive pointer operations must be separatedby at least three frames in which the pointer valueremains constant.

•The pointer value of 0 indicate that the VC-4 starts in the bytes location that immediately follows the last H3 byte.

MEANING OF POINTER VALUE

1 2 3 4 5 6 7 8 9 10

123456789123456789

AUG 270

H1 Y Y H2 1* 1* H3 H3 H3 - - - - 86 - -

Negative Justification opportunoity (3 byte)Positive justification opportunity (3 byte)

125µs

250µs

521522

7820 86H1 Y Y H2 1* 1* H3 H3 H3

1K2 87 87

K2

AU-3 POINTER OFFSET NUMBERING.

85 86 86

521521

7827828686

Positive justification•If the frame rate of the VC-4 is slow w.r.t. that of the AU-4, then the alignment of the VC-4 must periodically slip back in time and pointer value Must be incremented by one.

•This operation is indicated by inverting bits 7,9,11,13,15(I bits) of the pointer word.

•There majority vote of decision will be acceptedBy the receiver.

•Three positive justification bytes appear immediately after the last H3 byte in the AU-4 frame inverted I bits.

•The data will be shifted by three byte.

•Subsequent pointers will contain the new offset.

1 2 3 4 5 6 7 8 9 10

125µm

250µm

375µm

500µm

123456789

1

4

91

4

91

4

9

AUG 270Start of VC-$

n-1 n n n n+1 n+1

H1 Y Y H2 1* 1* H3 H3 H3

FRAME 1

H1 Y Y

H1 Y Y

H1 Y Y

H2 1* 1

H2 1* 1

H2 1* 1

H3 H3 H3

H3 H3 H3

H3 H3 H3

POINTER VALUE (N)

n-1 n n n n+1 n+1

POINTER VALUE (I -BITS INVERTED))

POSITIVE JUSTIFICATION BYTES (3 BYTE0

n-1 n n n n+1 n+1

FRAME 2

FRAME-3

FRAME 4

POINTER VALUE (N+1)

n-1 n n n n+1 n+1

AU-4 POINTER ADJUSTIFICATION OPERATION- - POSITIVE JUSTIFICATION

Negative justification•If the frame rate of the VC-4 is too fast w.r.t. that of the AU-4, then the alignment of the VC-4 must periodically be advanced in time and pointer value must be decremented by one.

•This operation is indicated by inverting bits 8,10,12,14,16(D bits) of the pointer word.

•There majority vote of decision will be acceptedby the receiver.

•Three negative justification bytes appear immediately in the H3 bytes in the AU-4 frame containing inverted D bits.

•The data will be shifted by three byte.

•Subsequent pointers will contain the new offset.

1 2 3 4 5 6 7 8 9 10

125µm

250µm

375µm

500µm

123456789

1

4

91

4

91

4

9

AUG 270Start of VC-$

n-1 n n n n+1 n+1

H1 Y Y H2 1* 1* H3 H3 H3

FRAME 1

H1 Y Y

H1 Y Y

H1 Y Y

H2 1* 1

H2 1* 1

H2 1* 1

H3 H3 H3

H3 H3 H3

H3 H3 H3

POINTER VALUE (N)

n-1 n n n n+1 n+1

POINTER VALUE (I -BITS INVERTED))

POSITIVE JUSTIFICATION BYTES (3 BYTE0

n-1 n n n n+1 n+1

FRAME 2

FRAME-3

FRAME 4

POINTER VALUE (N+1)

n-1 n n n n+1 n+1

AU-4 POINTER ADJUSTIFICATION OPERATION- - POSITIVE JUSTIFICATION

New data flag ( NDF)•Bits (1-4) of pointer word carry an NDF whichallows an arbitrary change of the pointer valueIt that change is due to a change in the payload.•Normal(disable) operation is indicated by a “0110” code•Inverted(enable) operation is indicated by a “1001”code•An NDF operation is enabled when 3 out of 4bits match with the pattern “1001”•An NDF operation is disabled when 3 out of 4bits match with the pattern “0110”

•The remaining values (‘0000’ ‘0011” “0101”“1010” “1100” and “1111”) should be interpretedas invalid.

Pointer generationThe following summarizes the rules for generatingthe AU-n pointer.

1. During normal operation, the pointer locatesthe start of the VC-4 within the AU-4 frame. the NDF is set to “0110”.2. The pointer value can be changed by operation3,4,5.3.If a positive justification in required.A-The current pointer value is sent with I-bitsInverted,and the positive justification opportunity is filled with dummy information.

B- Subsequently pointer value contain in the previousPointer is incremented by one.C- No subsequent increment or decrement operationis allowed at least three frames following this operation4-If a negative justification is required.A-The current pointer value is sent with D-bitsinverted,and the negative justification opportunity is over written with actual data.B- Subsequently pointer value contain in theprevious pointer is decremented by one.

C- No subsequent increment or decrement operationis allowed at least three frames following this operation5- A-If the alignment of the VC-4 changes for anyreason other than rules 3 or 4,the new pointer value shall be sent accompanied by NDF set to “1001”B-The NDF only appears in the first frame thatcontains the new values.C-The location of the VC-4 begins at the first occurrence of the offset indicated by the pointer.D- No subsequent increment or decrement operationis allowed at least three frames following this operation

Pointer interpretationThe following summarizes the rules for interpretingthe AU-n pointer.1. During normal operation, the pointer locatesthe start of the VC-4 within the AU-4 frame.

2.Any variation from the current pointer value is ignored unless a new value is received three times Consecutively or it is preceded by one of rules3,4 or5 .Any consistent new value received three times consecutively overrides rule 3 or 4.

Pointer interpretation (continued)3- If the majority of the I- bits of the pointer word areinverted,positive justification operation is indicated.As a result pointer value will be incremented by one.

4- If the majority of the D- bits of the pointer word are inverted,negative justification operation isindicated.As a result pointer value will bedecremented by one.

5-If the NDF is interpreted as enabled, then new pointer value will set in first frame only.

AU-4 concatenation pointers always to show that the multi container-4 payload carried in a single should be kept. For example STM-4 & STM-16.

TU-3 pointer•TU-3 Pointer provides a method of allowing Dynamic alignment of VC-3 within the TU-3 frame,Independent of the actual content of the VC-3.

•Three individual pointers are contained in three Separate bytes H1,H2,H3.•Actual pointer is in the bytes H1 andH2 Only

ALTTC GZB TX-I/SDH/POINTER 29

J1

B3

C2

G1

F2

H4

F3

K3

N1

J1

B3

C2

G1

AU-4 POINTER

AU-4 POINTER

FIXE

D S

TUF F

F IXE

D S

TUF F

H1

H2

H3

H1

H2

H3

H1

H2

H30

85

0

85

0

85

1

86

84 84 84

H1

H2

H3

H1

H2

H3

H1

H2

H30 0 0 1

764 764 764

84 84 84

593 594 594 594

261

AUG=9*270

TU-1 POINTER•TU1 pointer is contained in the V1 and V2 bytes of the TU1 multi-frame

•V1, V2 & V3 together form a pointer setSimilar to Hi,H2&H3 of VC-3

•Here two ‘s’ bits(5&6) indicate the Type of the TU(it may contain 2mb or 1.5 mb)

J2

N2

K4

V5V1

V2

V3

V4

TU12VC12

140BYTES

144BYTES

TU-12 POINTER OPERATION•In the normal course the first byte read bythe pointer will be the first byte just after theV3 byte . •If the VC-12 is fast or slow Then pointer isincremented or decremented

•Followed by negative (V3)or positive Justification respectively first byte just afterV3 will be =ve justification byte

•Normally the VC-12 is 140 bytes in 500microseconds .•Pointer can take care of one byte shift eitherway.•Hence the minimum and maximum allowable range for the rate of VC-12 will be

139*8*1000000/500= 2224kb/s .

141*8*1000000/500=2256kb/sOr

Normal rate is 140*8*1000000/500=2240kb/s

Limits of TU-12 Pointers

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