1. Fiber Optic Communication By
Engr. Muhammad Ashraf Bhutta

2. Lecture Outlines SDH Overview
Frame structure and multiplex-ing methods
Overheads and Pointers

3. SDH Overview Background of SDH Disadvantages of PDH Advantages of SDH
Disadvan-tages of SDH

4. Background about SDH emergence
What is SDH--Synchronous Digital Hierarchy. Similar to
PDH，they are all digital signal transmission system.
Why did SDH emerge?
1)What we need in info-society:
huge volume of info, and digital, integrated, personal.
2)What we want the transmission network to be:
Broadband---info-highway
Standard---universal interface all over the world

5. Disadvantages of PDH: 1 Interfaces
Electrical interfaces---only regional standards, no universal standard.
3 rate hierarchies for PDH:European(2Mb/s) Japanese, North American(1.5Mb/s).
Optical interfaces---no standards at all, manufacturers develop at their will.

6. Multiplexing methods:
Asynchronous Multiplexing for PDH:
The location of low-rate signals in high-rate signals is not
regular nor predictable. So it is impossible to directly
add/drop low-rate signals from high-rate signals.
Where
did I put
the signals?

7. Low-rate signals have to be separated from high-rate signals level by level. Multiple levels of multiplexing/de-multiplexing cause signals to deteriorate, it is not suitable for huge-volume transmission.

8. OAM 4 No universal network management interface
OAM function affects the maintenance cost.It is determined
by the number of overhead bytes(redundant bytes);
There are VERY few redundant byes available in PDH
signals which can be used as OAM purpose, so OAM in PDH
is very poor, it is unreliable either.
4 No universal network management interface
It is hard to set up an integrated network
management. No way to form a universal TMN.
PDH is inappropriate to transmit huge-volume signals, so
SDH came to play the part.

9. Advantages of SDH: 1 Interfaces
Electrical interfaces:standard rate hierarchy(transmission speed level)
The basic rate level is called Synchronous Transfer Module(STM-1), the other rate levels are the multiple of STM-1.
Optical interfaces:only scramble the electrical signals.
SDH: optical code pattern is scrambled NRZ,
PDH: optical code pattern is scrambled mBnB.

10. SDH:high-rate signal is exactly 4 times that
SDH Signals
Bit rate(Mb/s)
STM-1
or 155M
STM-4
or 622M
STM-16
or 2.5G
STM-64
or 10G
SDH:high-rate signal is exactly 4 times that
of the next low-rate signal.

11. SDH:4×STM-1=STM-4 ；4×STM-4=STM-16

12. 2 Multiplexing methods:
low-rate SDH→high-rate SDH(e.g.:4  STM-1→STM-4).
Uses byte interleaved multiplexing method.
STM-1
STM-4
Byte interleaved
multiplexing

13. Byte interleaved multiplexing

14. PDH Pkg Packing PKG a PKG b Other signals→SDH:
Using pointers to align the low-rate signals in SDH frame
,so the receivers can directly drop low-rate signals.E.g.:
PDH
Packing
Pkg
Alignment
PKG a
PKG b
STM-1

15. 3 OAM 4 Compatibility More bytes in SDH frame structure are used for
OAM purpose, about 5% of total bytes. SDH boasts
of high capability of OAM.
4 Compatibility
SDH is compatible with the existing PDH system.
SDH allows new types of equipment to be used,
allows broadband access, such as ATM.

16. SDH compatibility schematics
PDH, ATM
FDDI signals
packing
SDH
network
Package
package
STM-N
STM-N
packing
transmit
transmit
transmit
unpacking
PDH, ATM
FDDI signals

17. Disadvantages of SDH 2M STM-1 (155M) 34M 140M
1 low bandwidth utilization ratio--- contradiction
between efficiency and reliability.
140M
34M 2M
1140M=642M
334M=482M
632M
STM-1
(155M)
2 Mechanism of pointer adjustment is complex, it can
cause pointer adjustment jitters
3 Large-scale application of software makes SDH system
vulnerable to viruses or mistakes.

18. Frame Structure and Multiplexing methods
Multiplexing Procedure
Components and functions
140M
34M 2M
STM-N

19. STM-N Frame Structure Transmission direction 1 SOH 3 4 AU-PTR
9×270 ×N bytes
Transmission direction 1
Transmit
left to right
up to down
SOH 3 4
AU-PTR
STM-N payload
(including POH) 5
SOH 9
9×N
261×N
270×N columns

20. 1 Characteristics of SDH signals:
block frame in units of bytes(8bit),
transmission---from left to right, from top to bottom,
frame frequency constant frames/s,
frame period 125us.
2 Composition of SDH signals:
1) Payload:
It is where we put all the information in STM-N frame
structure. All kinds of effective info, such as 2M, 34M ,
140M are first packed before being stored here. Then
they are carried by STM-N signals over the SDH network.

21. If we should consider STM-N signal to be a truck, then
info payload would be the carriage of the truck. In order to
monitor the transmission status of the goods during
transportation, POH are added to each information package.
Pkg
Payload
Low-rate signals 1
Low-rate signals n
loading
POH
packing
STM-N

22. 2) Section Overhead:
Accomplishes monitoring of STM-N signal streams. To check
whether the “goods” in STM-N “carriage” is damaged or not.
Regenerator Section Overhead(RSOH): monitor the overall
STM-N signals.
Multiplex Section Overhead(MSOH): monitor each STM-1
in STM-N signal.
RSOH, MSOH and POH set up SDH layered
monitoring mechanism.

23. Sections and Paths SDH Section signal (SOH) low-rate path signal(POH).
SDH
Section signal
(SOH)
Low-rate signal 1
Low-rate signal 2
Low-rate signal n
low-rate path signal(POH)
Sections and Paths

24. 3) Administrative Unit Pointer(AU-PTR):
Indicates the location of low-rate signals in STM-N
frame(payload), makes the location of low-rate
signals in high-rate signals predictable.

25. According to the value of AU, the receiver can directly
drop low-rate signals from STM-N frame. That is to
say we can get the “goods” directly from the “carriage”
if we know the label of the “goods”.
Because the “goods” are placed regularly in the
“carriage”, we only need to know the first piece of
“goods”.

26. Receiving: Sending: According to the value of
AU-PTR, get the first info
package, through the
regularity of byte interleaved
multiplexing, get the other
packages
Sending:
AU-PTR indicates the first
info package
键入文本
键入文本
(SDH transmission
network)

27. For low-rate signals such as 2M, 34M. We need two-levels
of pointers to align.
First, small information “goods” is packed into middle
information “goods”. Tributary unit pointer(TU-PTR)
is used to align the location of small “goods” in middle “goods”.
Then these middle “goods” are packed into big “goods”,
AU-PTR is to align the location of middle info package. 2M
34M
TU-PTR
Primary alignment
AU-PTR
Secondary alignment

28. Multiplexing procedures of SDH
low-rate SDH→high-rate SDH:
byte interleaved multiplexing, 4 into 1.
PDH signals→STM-N: synchronous multiplexing:
140M→STM-N
34M→ STM-N
2M→STM-N
Multiplexing is based on the multiplexing route diagram.
ITU-T defines several different multiplexing routes, but for
any country or region, the method is unique.

29. SDH Multiplexing Hierarchy
139264kbit/s
STM-N
AUG
AU-4
VC-4
C-4 ×3
SDH signal
TU-3
TUG-3
VC-3 ×7
34368kbit/s
C-3
Pointer processing
TUG-2 ×3
Align adjustment
TU-12
2048kbit/s
VC-12
C-12
Multiplexing
Mapping
PDH signals

30. C4 VC4 140M multiplexing procedures(140M →STM-N) P O H 1 1 POH 140M 9
Rate
Adaptation
POH C4
VC4
To be continued
140M 9 9
125us
125us
C4---Container 4: A standard info structure corresponding to 140M,
performs bit rate justification.
VC4---Virtual Container 4: A standard info structure corresponding
toC4, performs real-time performance monitoring of 140M

31. 140M multiplexing procedures
AU-4
STM-1 1 1
(continue)
RSOH
payload
AU-PTR 1
270xN
alignment
SOH
AU-PTR 1 1 9
MSOH 9 9 10
270 1
270
STM-N
125us
125us
AU-4---Administrative Unit 4, a info structure
corresponding toVC4, performs pointer alignment.
140M—VC4—AU-4—STM-1,
One STM-1 can only incorporate one 140M signal. 9
125us

32. C3 VC3 34M multiplexing procedures P O H 1 1 POH 34M 9 9 1 84 1 85
Rate adaptation
To be continued
34M 9 9
125us
125us
C3---Container 3: A standard info structure corresponding to 34M,
performs bit rate justification.
VC3---Virtual Container 3: A standard info structure corresponding
to C4, performs real-time performance monitoring of 140M

33. VC4 34M multiplexing procedures TU-3 TUG-3 P O R R H 125us (continue)
PTR H1 H2 H3
Fill
Gap R
BIM
125us 1 86 9
261 ×3
TU3---Tributary Unit 3: A standard info structure corresponding to
VC3, performs primary alignment.
TUG3---Tributary Unit Group 3: A standard info structure
corresponding toTU3.
34M—VC3—TU3—TUG3；3 TUG3—VC4—STM-1；
One STM-1 can hold 3 34M.

34. C12 VC12 TU12 2M multiplexing procedures POH 1 1 1 2M 9 9 9 PTR 1 4
Primary
Alignment
Rate
Adaptation
C12
POH
VC12
TU12
To be continued 2M 9 9 9
PTR
125us
125us
125us

35. 2M multiplexing procedures (2M →VC4)
C12--Container 12: A standard info structure
corresponding to 2M, performs bit rate justification
for 2M signals, 4 basic frames constitute a multi-frame.
VC12---Virtual Container 12:A standard info structure
corresponding to 2M, performs real-time monitoring.
TU12---Tributary Unit 12: A standard info structure
corresponding to VC12, performs primary pointer
alignment forVC12.

36. TUG3 TUG2 2M multiplexing procedures (2M →VC4) R R 125us 125us 1 86 1×3 ×7
Byte
Interleaved
Multiplexing
Byte Interleaved
Multiplexing
TUG2
TUG3
R R
(continue) 9 9
125us
125us

37. 2M Multiplexing procedures(2M →VC4)
TUG2---Tributary Unit Group 2
TUG3---Tributary Unit Group 3
2M—C12—VC12—TU12；3TU12—TUG2；
7 TUG2—TUG3；3TUG3—VC4—STM-1。
One STM-1 is able to hold 3×7×3= 63 2M.
Multiplexing structure for 2M is

38. SDH Multiplexer Concept of multi-frame: STM-11# 3# 2# 4#
63 2M
Concept of multi-frame:
4 C12 basic frames make up
1 multi-frame.
Both basic frames and
multi-frame carry the same
2M signal.
One basic frame can hold
the info segment of 2M
signal during 125us period.
One multi-frame holds the
info for 2M signal during
500us period.

39. Relations between info structures
VC12
TU12 E3 C3
VC3
TU3 E4 C4
VC4

40. Summary STM-N frame structure and functions of
different parts of the frame
Methods for multiplexing PDH into STM-N frames
140M multiplexed into STM-N frames
34M multiplexed into STM-N frames
2M multiplexed into STM-N frames

41. Overhead Pointers Path Overhead Section Overhead Overhead and Pointers
AU-PTR
TU-PTR

42. Overhead
SOH
POH
RSOH
MSOH
VC4
POH
VC12
POH
(LPOH)
(HPOH)

43. Layered monitoring

44. SOH(take STM-1 as an example) 1 2 3 4 5 6 7 8 9 A1 * A1 * A1 * A2 * A2 * A2 * J0 * * * B1 E1 F1
RSOH D1 D2 D3
AU-PTR B2 B2 B2 K1 K2 D4 D5 D6 D7 D8 D9
MSOH
D10
D11
D12 S1 M1 E2
Bytes reserved for domestic use
Marked bytes are not scrambled *

45. 1) Framing bytes:A1,A2 to locate the frame heads
STM-N
Signal stream

46. N Y Frame Head? Give OOF Over 3ms Generate LOF Insert AIS Next process
Found
A1,A2?
Give OOF Y
Over 3ms
Generate LOF
Next process
Insert AIS

47. 2) DCC Data Communication Channel bytes:D1—D12
An info channel for OAM between NE-NE
D1-D3 is in Regenerator section(DCCR),
D4-D12 is in Multiplex section(DCCM),
OAM info includes: performance monitoring, alarms inquiry, command issue,etc.
DCC channel NM
UTP

48. 3) Order wire bytes: E1,E2
Each provides a 64kb/s order wire digital telephone.
E1is for RS order wire
E2 is for MS order wire
E2can not be used by a REGs
4) Bit interleaved parity byte:B1
Performs real-time monitoring over the signal stream

49. Bit Interleaved parity

50. If error blocks occurred
B1 working mechanism:
Detect B1
Insert B1
SDH
Equipment
Sending
SDH
Equipment
Receiving
STM-N
If error blocks occurred
produce: RS-BBE
performance event

51. If error blocks occurred
5) Bit interleaved Parity B2 byte
monitor the error blocks of MS
Detect B2
Insert B2
SDH
Equipment
Sending
SDH
Equipment
Receiving
STM-N
If error blocks occurred
produce: MS-BBE
performance event

52. STM-N 6) Multiplex section Remote Error Indication byte:M1
Sent from receiver to sender
Informs the sender: the error blocks detected by receiver
through B2
SDH
Equipment
Sender
Receiver
STM-N
Error blocks found
produce: MS-BBE
performance event
Send M1
byte
M1 received
produce: MS-REI

53. 7) Automatic Protection Switching(APS) bytes---K1,K2
Carries APS protocol for MSP switching
MS Remote Defect Indication byte:
K2(b6-b8)=111, indicates that all “1” signals have
been received, receiver will give MS-AIS alarm
K2(b6-b8)=110, indicates that MS-RDI has been
received, which means the counter-part has received
signal deterioration, such as MS-AIS, RLOF etc.

54. K2 Detection Found 110 111 K2(b6-b8) Giving MS-AIS Sending back MS-RDI
Producing
MS-RDI

55. STM-N Receive K2(110) produce: MS-RDI alarm event Find K2(111)
produce: MS-AIS
alarm event
SDH
Equipment
Sender
SDH
Equipment
Receiver
STM-N
Sending back K2
(110)

56. 8) Synchronous Status byte S1(bit5~8)
For synchronous status indication
The smaller the value of S1, the higher the quality of synchronous clock!

57. 2 Path Overhead Classification: VC4 POH Lower-order POH--VC12
Higher-order POH---VC4
Difference:
VC-4 macro, VC-12 micro
VC-4 includes VC-12
VC4
POH
VC12
POH
(HPOH)
(LPOH)