SDH (Synchronous Digital Hierarchy) is a standard technology for synchronous data transmission that provides faster and less expensive network interconnection than traditional PDH (Plesiochronous Digital Hierarchy) equipment. PDH uses asynchronous multiplexing which means low rate signals cannot be directly added or dropped from high rate signals, requiring multi-stage addition and dropping. PDH also lacked universal standards for electrical and optical interfaces and had limited overhead bytes for network management functions. SDH was developed to address these disadvantages of PDH through synchronous multiplexing and a standardized frame structure and network management system.

1. ‫خرد‬‫و‬‫جان‬ ‫خداوند‬‫بنام‬
1

2. SDH (Synchronous Digital Hierarchy)
2

3.  Transmission Technology
 Definitions
 PDH
 SDH Overview
 Advantages of SDH
 SDH Frame Structure
 SDH Network Elements
 References
3

4. Analogue Transmission
Until about 1970 transportation of voice signals was achieved by
carrying analogue signals over copper twisted pairs. Frequency
Division Multiplexing (FDM) was used on long routes to combine
multiple traffic signals on a single coaxial cable.
Digital Transmission
In the early 1970s, digital transmission systems began to appear,
utilizing Pulse Code Modulation (PCM) , which enables analogue
speech signals to be represented in a binary form. By this method, the
standard 300 to 3400 Hz analogue telephone bandwidth is converted
4

5. into a 64kbit/s digital bit stream. The analogue speech signals are
sampled, quantized (rounded to the nearest integer value) and then
encoded to give a binary pattern.
Principles of PCM
5

6. Time division Multiplexing
The method used to combine multiple 64 Kbit/s digital bit streams
into a single high speed bit stream is known as Time Division
Multiplexing (TDM).
In the standard TDM Scheme, thirty 64 Kbit/s channels (30 Ch.) were
combined with two additional channels carrying control and signaling
information, to produce a structure with a bit rate of 2.048Mbit/s (for
simplicity, 2Mbit/s).
6

7. Digital Hierarchy
The standard 2Mbit/s signal was not sufficient to cope with the traffic
loads occurring in the network. In order to avoid using large numbers
of 2Mbit/s links, it was decided to create a further level of
multiplexing. The standard adopted in Europe involved the
combination of four 2Mbit/s channels to produce a single 8Mbit/s
channel (more exactly, 8.448Mbit/s). As the need arose, further levels
of multiplexing were added to the standard at 34Mbit/s, 140Mbit/s,
and 565Mbit/s to produce a full hierarchy of bit rates.
7

8. SDH (Synchronous Digital Hierarchy) is a standard technology for
Synchronous data transmission on optical media.
It is the international equivalent of Synchronous Optical Network.
SONET (Synchronous Optical Network) is the American standard for
synchronous data transmission on optical media.
Both technologies provide faster and less expensive network
interconnection than traditional PDH (Plesiochronous Digital
Hierarchy) equipment.
Plesiochronous: (communication) almost synchronous
8

9. PDH (Plesiochronous Digital Hierarchy)
Pre-SDH Transmission Technology
PDH Signal with a higher transmission rate is obtained by multiplexing
several lower-rate signals.
9

10. Tributary access in PDH
Since PDH adopts asynchronous multiplexing method, low rate signals cannot
be directly added or dropped from high-rate signals. Therefore, adding and
dropping must be conducted level by level.
10

11. 11

12. Disadvantages of PDH
 No universal standard for Electrical interface. Each of regional
standards has different rate levels , frame structures and
multiplexing methods. This makes it difficult for international
interconnection.
 No universal or regional standard for Optical interface. Different
vendors use different line codes. This causes difficulties for
network structuring, management, and network interconnection.
12

13.  Adopting step-by-step multiplexing/de-multiplexing method
increases the cost, power consumption , complexity and
impairment to the signal.
 In PDH frame structure, there are few overhead bytes used for
Operation, Administration and Maintenance (OAM) functions.
 No universal network management interface. Different vendors
provide different network management systems.
13

14. ‫معايب‬‫سيستم‬PDH
‫در‬‫سيستمهاي‬PDH‫اي‬‫ر‬‫ب‬‫اينترفيس‬‫الكتريكي‬‫د‬‫ر‬‫استاندا‬‫جهاني‬‫وجود‬‫نداشته‬‫و‬‫فقط‬‫هاي‬‫ر‬‫معيا‬‫م‬‫نطقه‬‫اي‬
،‫پايي‬‫و‬‫ار‬‫آمريكاي‬‫شمالي‬‫و‬‫اپني‬‫ژ‬‫وجود‬‫د‬‫ر‬‫دا‬.‫هر‬‫يك‬‫از‬‫اين‬‫اينترفيس‬‫هاي‬،‫الكتريكي‬‫سطوح‬‫سرعت‬،‫ساختار‬
‫فريمينگ‬‫و‬‫شهاي‬‫و‬‫ر‬‫مالتي‬‫پلكس‬‫مختلفي‬‫ند‬‫ر‬‫دا‬.‫اين‬‫موضوع‬‫اي‬‫ر‬‫ب‬‫تباط‬‫ر‬‫ا‬‫بين‬‫املللي‬‫مشكالت‬‫ي‬‫ا‬‫ر‬‫ايجاد‬‫ميكند‬.
‫اي‬‫ر‬‫ب‬‫اينترفيس‬،‫ي‬‫ر‬‫نو‬‫هيچ‬‫د‬‫ر‬‫استاندا‬‫جهاني‬‫يا‬‫منطقه‬‫اي‬‫وجود‬‫د‬‫ر‬‫ندا‬.‫به‬‫همين‬‫دليل‬‫مديريت‬‫شب‬‫كه‬‫هاي‬‫ي‬‫ر‬‫نو‬
‫كه‬‫ات‬‫ز‬‫تجهي‬‫آنها‬‫ساخت‬‫خانجات‬‫ر‬‫كا‬‫مختلف‬‫مي‬‫باشد‬‫با‬‫مشكالتي‬‫مواجه‬‫است‬.
14

15. ‫ش‬‫و‬‫ر‬‫مالتي‬‫پلكس‬PDH‫همزمان‬‫نمي‬‫باشد‬.‫به‬‫ت‬‫ر‬‫عبا‬‫ديگر‬‫سوار‬‫يا‬‫پياده‬‫كردن‬(Add/Drop)
‫سيگنالهاي‬‫سرعت‬‫پايين‬‫از‬‫سيگنالهاي‬‫سرعت‬‫باال‬‫ر‬‫بطو‬‫مستقيم‬‫انجام‬‫نمي‬‫شود‬‫و‬‫بايد‬‫مرحله‬‫به‬‫مرحله‬
‫انجام‬‫شود‬.‫به‬‫عنوان‬‫مثال‬‫اي‬‫ر‬‫ب‬‫پياده‬‫كردن‬‫يك‬‫سيگنال‬2Mb/s‫از‬140Mb/s‫بايد‬‫سه‬‫مرحله‬‫دي‬
‫مالتي‬‫پلكس‬‫انجام‬‫شود‬.‫اين‬‫موضوع‬‫حجم‬‫ات‬‫ز‬‫تجهي‬‫ا‬‫ر‬‫ايش‬‫ز‬‫اف‬‫ميدهد‬‫و‬‫هزينه‬،‫ها‬‫توان‬‫مصرفي‬‫و‬‫پ‬‫يچيدگي‬
‫ات‬‫ز‬‫تجهي‬‫ا‬‫ر‬‫باال‬‫مي‬‫برد‬.‫از‬‫آنجا‬‫كه‬‫آيند‬‫ر‬‫ف‬‫پياده‬‫و‬‫سواركردن‬‫سيگنالهاي‬‫سرعت‬‫پايين‬‫از‬‫سيگن‬‫الهاي‬‫سرعت‬
‫باال‬‫و‬‫برعكس‬‫در‬‫طي‬‫چند‬‫مرحله‬‫مالتي‬‫پلكس‬‫و‬‫دي‬‫مالتي‬‫پلكس‬‫انجام‬‫مي‬،‫شود‬‫در‬‫ل‬‫طو‬‫اين‬‫آين‬‫ر‬‫ف‬‫دها‬‫يب‬‫ر‬‫تخ‬
‫سيگنال‬‫ايش‬‫ز‬‫اف‬‫يافته‬‫و‬‫كيفيت‬‫انتقال‬‫كاهش‬‫مي‬‫يابد‬.‫اين‬‫موضوع‬‫در‬‫سيستمهاي‬‫انتقال‬‫ظر‬‫فيت‬‫باال‬‫اهميت‬
‫پيدا‬‫ميكند‬‫و‬‫دليلي‬‫است‬‫بر‬‫اينكه‬‫ا‬‫ر‬‫چ‬‫سيستم‬PDH‫بيشتر‬‫از‬‫اين‬‫گسترش‬‫نيافته‬‫است‬.
15

16. ‫در‬‫ساختار‬‫فريم‬PDH‫تعداد‬‫محدودي‬‫بايت‬Overhead‫اي‬‫ر‬‫ب‬‫انجام‬‫عمليات‬OAM(‫بهره‬،‫ي‬‫بردار‬
،‫يت‬‫ر‬‫مدي‬‫ي‬‫نگهدار‬)‫وجود‬‫د‬‫ر‬‫دا‬.‫كم‬‫بودن‬‫تعداد‬‫بايتهاي‬Overhead‫در‬‫سيگنالهاي‬PDH‫از‬‫معايب‬
‫اينگونه‬‫سيستمها‬‫اي‬‫ر‬‫ب‬،‫يت‬‫ر‬‫مدي‬‫ينگ‬‫ر‬‫مانيتو‬‫و‬‫يه‬‫ز‬‫تج‬‫و‬‫تحليل‬‫مها‬‫ر‬‫آال‬‫مي‬‫باشد‬.
‫ماني‬‫ز‬‫كه‬‫خريدار‬‫ات‬‫ز‬‫تجهي‬‫اتي‬‫ر‬‫مخاب‬‫ا‬‫ر‬‫از‬‫يك‬‫نده‬‫ز‬‫سا‬‫ي‬‫خريدار‬‫مي‬‫كند‬‫بايستي‬‫سيستم‬‫يت‬‫ر‬‫مدي‬‫شبكه‬‫به‬‫اه‬‫ر‬‫هم‬
‫ات‬‫ز‬‫تجهي‬‫به‬‫خريدار‬‫ائه‬‫ر‬‫ا‬‫گردد‬.‫توسط‬‫شندگان‬‫و‬‫فر‬‫مختلف‬‫سيستمهاي‬‫يت‬‫ر‬‫مدي‬‫شبكه‬‫مختلف‬‫ي‬‫ائه‬‫ر‬‫ا‬‫مي‬
‫شوند‬.‫اين‬‫ر‬‫بناب‬‫قسمتهاي‬‫مختلف‬‫يك‬‫شبكه‬‫ممكن‬‫است‬‫سيستمهاي‬‫مديريتي‬‫مختلفي‬‫ا‬‫ر‬‫د‬‫ر‬‫مو‬‫استفاده‬‫ار‬‫ر‬‫ق‬
‫دهند‬‫كه‬‫اين‬‫مطلب‬‫مانعي‬‫اي‬‫ر‬‫ب‬‫تشكيل‬‫مديريت‬‫شبكه‬‫چه‬‫ر‬‫يكپا‬‫است‬.
16

17. ‫به‬‫دليل‬‫معايب‬،‫نامبرده‬‫سيستم‬‫انتقال‬PDH‫ر‬‫بطو‬‫قابل‬‫توجهي‬‫مانع‬‫توسعه‬‫شبكه‬‫انتقال‬‫مي‬‫شود‬.
‫اين‬‫ر‬‫بناب‬‫شبكه‬‫ي‬‫ر‬‫نو‬‫همزمان‬SONET(Synchronous Optical Network)‫كه‬‫شامل‬‫مجموعه‬
‫اي‬‫از‬‫دهاي‬‫ر‬‫استاندا‬‫انتقال‬‫ديجيتال‬‫بود‬‫پيشنهاد‬‫شد‬‫و‬‫پس‬‫از‬‫پذيرفته‬‫شدن‬‫با‬‫اتي‬‫ر‬‫تغيي‬‫به‬‫س‬‫لسله‬‫اتب‬‫ر‬‫م‬‫انتقال‬
‫ديجيتال‬‫همزمان‬SDH‫تغيير‬‫نام‬‫داد‬.
17

18. SDH (Synchronous Digital Hierarchy) is a transmission protocol for
high-speed, high-capacity optical transmission systems which defines
the characteristic of digital signals, including frame structure,
multiplexing method, digital rates hierarchy, interface code pattern,
and so on.
18

19. Why did SDH emerge?
Information Society requires:
 A variety of telecommunication services.
 Networks that can transmit, switch and process a large amount of
information.
 Networks to be digital, integrated and intelligent.
This requires modern transmission networks develop toward:
 High Speed (Broad Bandwidth)
 Universal Interface
19

20. Characteristics of the SDH
Bit Rate Levels
According to the ITU-T specifications, the bit rate of the lowest level
SDH signal (base signal) is 155.520 Mb/s which is known as
“Synchronous Transport Module – 1” (STM-1).
Higher Bit Rate Levels are integer multiples of STM-1:
STM-1 155.52 Mb/s
STM-4 622.08 Mb/s
STM-16 2488.32 Mb/s (2.5Gb/s)
STM-64 9953.28 Mb/s (10Gb/s)
20

21. 21

22. Characteristics of the SDH
Byte Interleaved Multiplexing Method
Higher level signals are obtained by byte interleaved multiplexing
lower level signals.
22
STM-4
STM-1 A
STM-1 B
STM-1 C
STM-1 D

23. Characteristics of the SDH
Synchronization in SDH Networks
Digital signals in all the network elements in a SDH network are
controlled by a master clock. The signals are clock aligned to each
other, that is why they are named synchronous.
23

24. 24

25. Interface
SDH provides universal standards for both electrical and optical
interfaces, including standards on:
 Digital signal rate levels
 Frame structure
 Multiplexing method
 Monitoring & Management
So, SDH equipments from different vendors can be easily
interconnected.
25

26. Multiplexing Method
In SDH, almost direct access to a tributary signal in a line is possible.
Lower-rate signals can be directly added to or dropped from higher-
rate signals.
26
STM-N

27. ADMs (Add-Drop Multiplexers) are the most common type of network
elements. ADMs traditionally have a high-speed side (where the full
line rate signal is supported), and a low-speed side, which can consist
of electrical as well as optical interfaces. The low-speed side takes in
low-speed signals, which are multiplexed by the network element and
sent out from the high-speed side, or vice versa.
27

28. OAM Functions
Abundant overhead bits for OAM (Operations, Administration,
Maintenance) are arranged in the frame structure of SDH signal. This
greatly enforces the network monitoring function and reduces the cost
of system maintenance.
28

29. Introduction
For the convenience of signal analysis, the SDH frame structure is
illustrated as a rectangle block.
The STM-1 frame structure include 9 rows with 270 bytes each.
29

30. 30

31. Bit rate calculations
This formula calculates the Bit rate of a framed digital signal:
Bit Rate = Frame Rate × Frame Capacity
The frame capacity of a signal is the number of bits contained within a
single frame.
Frame Capacity = 270 bytes/row × 9 rows/frame × 8 bits/Byte =
19440 bits/frame
Frame period = 125 µs
Frame Rate = 1/125 µs = 8000 Hz = 8000 frames/second
31

32. The Bit Rate of STM-1 signal is calculated as follows:
Bit Rate = 8000 frames/second × 19440 bits/frame = 155,520,000
bit/s = 155.52Mbit/s
32

33. Frame Structure
The SDH frame structure consist of three parts:
1- Section Overhead (SOH) – auxiliary bytes to implement OAM
functions.
2- Administrative Unit Pointer (AU – PTR) – indicates the start location
of the Payload.
3- Payload – transports the tributary information.
33

34. The SOH can be classified into Regenerator Section Overhead (RSOH)
and Multiplex Section Overhead (MSOH). They respectively monitor the
corresponding sections.
To monitor the tributary signals on a real-time basis, Path Overhead
(POH) bytes are added in the payload area.
The POH together with the Payload form the Virtual Container (VC).
34

35. 35

36. The Virtual Container (VC) is used to transport a tributary signal
across the SDH network. The path followed by a VC within the network
may include many nodes, therefore the VC may be transferred from
one SDH transport system to another, many times on its path through
the network. Nevertheless, in most cases the VC is assembled at the
point of entry to the SDH network and disassembled only at the point
of exit.
Since the VC is opened only at the path end points, some of its signal
carrying capacity is dedicated to Path Overhead (POH).
36

37. The Path Overhead provides the facilities (alarm and performance
monitoring), required to support and maintain the transportation of
the VC between the end points.
VC
37

38. ‫ه‬‫ز‬‫و‬‫امر‬‫جهت‬‫انتقال‬‫سيگنالهاي‬‫ديجيتال‬‫از‬‫ش‬‫و‬‫ر‬‫سلسله‬‫اتبي‬‫ر‬‫م‬‫استفاده‬‫مي‬‫شود‬‫كه‬‫بر‬‫اساس‬‫سه‬‫ا‬‫د‬‫ر‬‫ستاندا‬
،‫پايي‬‫و‬‫ار‬‫آمريكايي‬‫و‬‫اپني‬‫ژ‬‫تدوين‬‫شده‬‫اند‬.‫جي‬‫و‬‫خر‬‫اين‬‫سيستمها‬‫سيگنال‬PDH‫يا‬‫سيگنال‬‫سلسله‬‫اتبي‬‫ر‬‫م‬‫غير‬
‫همزمان‬‫ناميده‬‫مي‬‫شود‬.‫اما‬‫اين‬‫شها‬‫و‬‫ر‬‫قادر‬‫به‬‫انتقال‬‫همه‬‫سيگنالها‬‫نيستند‬.‫با‬‫توجه‬‫به‬‫اين‬‫موضو‬‫ع‬‫و‬‫نيز‬‫ويژگيهاي‬
،‫ديگر‬‫سيستمهاي‬SDH‫و‬‫يا‬‫سلسله‬‫اتبي‬‫ر‬‫م‬‫همزمان‬‫توسط‬ITU-T‫د‬‫ر‬‫استاندا‬‫شد‬.
‫شبكه‬SDH‫يك‬‫شبكه‬‫همزمان‬‫است‬‫كه‬‫كليه‬‫اي‬‫ز‬‫اج‬‫آن‬‫از‬‫يك‬‫كالك‬‫واحد‬‫اي‬‫ر‬‫ب‬‫همزماني‬‫استفاده‬‫مي‬‫كنن‬‫د‬.‫نرخ‬
‫بيت‬‫پايه‬‫در‬‫اين‬‫شبكه‬155.52Mb/s‫است‬‫كه‬‫به‬‫آن‬STM-1‫گفته‬‫مي‬‫شود‬.‫اي‬‫ر‬‫ب‬‫ي‬ ‫دسترس‬‫به‬‫نرخ‬‫بيت‬
،‫بيشتر‬‫از‬‫مالتي‬‫پلكس‬‫سيگنال‬‫پايه‬‫استفاده‬‫مي‬‫شود‬.‫مقادير‬‫د‬‫ر‬‫استاندا‬‫شده‬‫اي‬‫ر‬‫ب‬‫نرخ‬‫بيتهاي‬‫باالتر‬‫تند‬‫ر‬‫عبا‬‫از‬:
STM-4, STM-16, STM-64, STM-256
38

39. ‫ساختار‬‫فريم‬STM-1‫ت‬‫ر‬‫بصو‬‫ايه‬‫ر‬‫آ‬‫اي‬‫دو‬‫بعدي‬‫از‬‫بايتها‬‫به‬‫ابعاد‬9‫سطر‬‫و‬270‫ن‬‫ستو‬‫نمايش‬‫داده‬‫مي‬‫شود‬.
‫ابتداي‬‫فريم‬‫بايتي‬‫با‬‫س‬‫ر‬‫آد‬(1,1)‫مي‬‫باشد‬‫و‬‫بايت‬‫انتهايي‬‫در‬‫موقعيت‬(270,9)‫ار‬‫ر‬‫ق‬‫گرفته‬‫است‬.‫عمليات‬‫انتقال‬
،‫بايتها‬‫سطر‬‫به‬‫سطر‬‫از‬‫بايت‬‫ل‬‫او‬‫تا‬‫ين‬‫ر‬‫آخ‬‫بايت‬‫ادامه‬‫مي‬‫يابد‬.
9‫ن‬‫ستو‬‫ل‬‫او‬‫از‬‫اين‬‫ل‬‫جدو‬‫جهت‬‫بايتهاي‬SOH‫و‬AU-PTR‫استفاده‬‫مي‬‫گردد‬.‫بايتهاي‬SOH‫به‬‫دو‬‫بخش‬
RSOH‫و‬MSOH‫تقسيم‬‫مي‬‫شوند‬.‫بقيه‬‫بايتهاي‬‫فريم‬‫نيز‬‫بخش‬‫محموله‬(Payload)‫ا‬‫ر‬‫تشكيل‬‫مي‬‫دهند‬.
‫ل‬‫طو‬‫اين‬‫فريم‬125µs‫است‬.
39

40. 40

41. SOH
‫بلوك‬SOH‫شامل‬‫بايتهاي‬‫اضافي‬(Overhead)‫م‬‫ز‬‫ال‬‫جهت‬‫ت‬‫ر‬‫نظا‬‫بر‬،‫خطا‬،‫يت‬‫ر‬‫مدي‬‫ي‬‫نگهدار‬‫و‬‫ل‬‫كنتر‬‫مي‬
‫باشد‬.SOH‫از‬9×8=72‫بايت‬‫تشكيل‬‫شده‬‫كه‬‫شامل‬‫دو‬‫قسمت‬‫مي‬‫باشد‬:
RSOH (Regenerator Section Overhead) 3 × 9 = 27 Byte
MSOH (Multiplex Section Overhead) 5 × 9 = 45 Byte
41

42. ‫شهاي‬‫و‬‫ر‬‫مالتي‬‫پلكسينگ‬‫در‬SDH
‫دو‬‫نوع‬‫مالتي‬‫پلكسينگ‬SDH‫وجود‬‫د‬‫ر‬‫دا‬:
1-‫مالتي‬‫پلكس‬‫سيگنالهاي‬‫اتب‬‫ر‬‫م‬‫پايين‬‫تر‬SDH‫به‬‫سيگنالهاي‬‫اتب‬‫ر‬‫م‬‫باالتر‬
‫نوع‬‫ل‬‫او‬‫مالتي‬‫پلكس‬‫اين‬‫موضوع‬‫ا‬‫ر‬‫بيان‬‫مي‬‫كند‬‫كه‬4‫سيگنال‬‫سرعت‬‫پايين‬‫مانند‬STM-1‫به‬‫يك‬‫سيگنال‬
STM-4‫و‬‫چها‬‫سيگنال‬STM-4‫به‬‫يك‬‫سيگنال‬STM-16‫تبديل‬‫مي‬‫شوند‬.
‫در‬‫حين‬‫مالتي‬‫پلكس‬‫بايت‬‫به‬‫بايت‬،‫بايتهاي‬‫اطالعات‬‫اصلي‬(Payload)‫و‬‫پوينترها‬‫ي‬‫هر‬‫فريم‬‫بر‬‫اساس‬‫مقادير‬
‫اوليه‬‫خودشان‬‫مالتي‬‫پلكس‬‫شده‬‫و‬‫در‬‫موقعيت‬‫هاي‬‫خاص‬‫خودشان‬‫ار‬‫ر‬‫ق‬‫داده‬‫مي‬‫شوند‬.
42

43. 2-‫مالتي‬‫پلكس‬‫سيگنالهاي‬‫سرعت‬‫پايين‬‫از‬‫قبيل‬140Mb/s - 34Mb/s - 2Mb/s‫به‬‫سيگنالهاي‬
SDH.
‫نوع‬‫دوم‬‫مالتي‬،‫پلكس‬‫اي‬‫ر‬‫ب‬‫تبديل‬‫سيگنالهاي‬‫سرعت‬‫پايين‬(Tributary) PDH‫به‬‫سيگنالهاي‬STM-N
‫د‬‫ر‬‫مو‬‫استفاده‬‫ار‬‫ر‬‫ق‬‫ميگيرد‬.
43

44. Payload(‫محموله‬)
‫سيگنالهاي‬‫فرعي‬2~140Mb/s (Tributary)‫در‬‫بخش‬‫محموله‬‫منتقل‬‫مي‬‫شوند‬.
‫تعداد‬‫بايتهاي‬Payload:2349=261×9
‫اطالعات‬‫ن‬‫و‬‫در‬،‫محموله‬‫تا‬‫سيدن‬‫ر‬‫به‬‫سطح‬‫متناظر‬‫در‬‫گيرنده‬،‫مقابل‬‫دست‬‫ده‬‫ر‬‫نخو‬‫باقي‬‫خواهد‬‫ماند‬.
‫جهت‬‫آشكار‬‫شدن‬‫صدمات‬‫احتمالي‬‫به‬‫محموله‬(‫سيگنالهاي‬‫سرعت‬‫پايين‬‫بسته‬‫بندي‬‫شده‬)‫در‬‫حين‬‫ان‬،‫تقال‬‫بايتهاي‬
POH (Path Overhead)‫به‬‫محموله‬‫اضافه‬‫مي‬‫گردد‬.POH‫به‬‫عنوان‬‫يك‬‫بخش‬‫از‬Payload(1‫ن‬‫ستو‬
‫و‬9‫سطر‬)‫به‬‫اه‬‫ر‬‫هم‬‫اطالعات‬‫در‬‫فريم‬STM-1‫ار‬‫ر‬‫ق‬‫داده‬‫مي‬‫شود‬‫و‬‫در‬‫شبكه‬SDH‫منتقل‬‫مي‬‫گردد‬.
44

45. Pointer(‫ه‬‫ر‬‫اشا‬‫گر‬)
AU-PTR (Administrative Unit Pointer)‫در‬‫سطر‬‫م‬‫ر‬‫چها‬‫ستونهاي‬‫ا‬‫الي‬9‫يم‬‫ر‬‫ف‬‫ار‬‫ر‬‫ق‬‫مي‬‫ند‬‫ر‬‫گي‬.
‫تعداد‬‫بايتهاي‬‫آن‬‫اي‬‫ر‬‫ب‬‫فريم‬STM-1،9‫بايت‬‫و‬‫اي‬‫ر‬‫ب‬‫فريم‬STM-N،9N‫بايت‬‫است‬.Pointer‫محل‬‫ع‬‫و‬‫شر‬
Payload‫ا‬‫ر‬‫نشان‬‫ميدهد‬.
‫ر‬‫همانطو‬‫كه‬‫گفته‬،‫شد‬‫سيگنالهاي‬‫سرعت‬‫پايين‬‫مي‬‫توانند‬‫ر‬‫بطو‬‫مستقيم‬‫از‬‫سيگنالهاي‬SDH‫پياده‬‫شوند‬‫يا‬‫بر‬
‫آن‬‫سوار‬،‫شوند‬‫ا‬‫ر‬‫ي‬‫ز‬‫موقعيت‬‫سيگنال‬‫سرعت‬‫پايين‬‫در‬‫فريم‬SDH‫سرعت‬‫باال‬‫قابل‬‫پيش‬‫بيني‬‫است‬.‫اين‬‫خاصيت‬
‫از‬‫طريق‬‫عملكرد‬‫بايت‬‫هاي‬AU-PTR‫انجام‬‫مي‬‫شود‬.‫به‬‫ت‬‫ر‬‫عبا‬‫ديگر‬‫پس‬‫از‬‫ترجمه‬‫و‬‫تفسير‬‫پوينتر‬‫مناسب‬،
‫ن‬‫بدو‬‫اينكه‬‫نياز‬‫به‬‫دي‬‫مالتي‬‫پلكس‬‫يا‬‫پياده‬‫ي‬‫ساز‬‫مرحله‬‫به‬‫مرحله‬‫سيگنال‬STM-1‫داشته‬،‫باشيم‬‫مي‬‫توانيم‬‫به‬
‫تمام‬‫شاخه‬‫هاي‬‫فرعي‬‫ي‬ ‫دسترس‬‫پيدا‬‫كنيم‬.
45

46. Structure of Transmission Path in SDH Network
46

47. In SDH Networks, a transmission path includes three Network Element
(NE) types:
SDH Terminal Multiplexer – which performs the insertion/removal of
tributary signals into SDH frames. Terminal Multiplexers are used to
combine plesiochronous and synchronous input signals into higher-
bit-rate STM-N signals.
47

48. Regenerator – A regenerator or amplifier is needed when due to long
distance between multiplexers, the signal level in the fiber gets
attenuated and becomes too low to drive a receiver. The regenerator
is sometimes called a repeater.
48

49. SDH Cross-Connect Switch – permits to change the routing of
tributary signals carried in SDH frames.
49

50. ‫در‬‫سيستم‬PDH‫اگر‬‫مي‬‫خواستيم‬‫يك‬2M‫ا‬‫ر‬‫به‬‫عنوان‬‫مثال‬‫در‬،‫اصفهان‬‫از‬‫مسير‬‫ان‬‫ر‬‫ته‬‫به‬‫مسير‬‫از‬‫ر‬‫شي‬
‫بفرستيم‬‫و‬‫افيك‬‫ر‬‫ت‬‫در‬‫سطح‬140Mb/s‫د‬‫ر‬‫و‬‫بدل‬‫مي‬،‫شد‬‫ابتدا‬‫در‬‫طرفين‬‫بايد‬140MB/s‫به‬
34Mb/s‫و‬‫سپس‬‫به‬8Mb/s‫و‬‫سپس‬‫به‬2Mb/s‫تبديل‬‫شوند‬.‫البته‬‫اينكار‬‫بار‬‫ر‬‫ه‬‫با‬‫گذر‬‫از‬‫پايانه‬‫هاي‬‫ي‬‫به‬
‫نام‬DDF(Data Distribution Frame)‫كه‬‫شامل‬‫تعدادي‬‫ترمينال‬‫ودي‬‫ر‬‫و‬‫و‬‫جي‬‫و‬‫خر‬‫مي‬،‫باشد‬‫ت‬‫ر‬‫صو‬
‫مي‬‫گيرد‬.‫سپس‬‫در‬‫سطح‬2M،‫اتصال‬‫با‬‫استفاده‬‫از‬‫كابل‬‫ار‬‫ر‬‫برق‬‫مي‬‫شود‬.
50

51. ‫اما‬‫در‬SDH‫با‬‫توجه‬‫به‬‫اينكه‬‫با‬‫استفاده‬‫از‬‫تكنيك‬‫پوينتر‬‫محل‬‫بايتهاي‬‫هر‬2M‫مشخص‬‫مي‬،‫باشد‬‫با‬‫فرماني‬‫نرم‬
‫ي‬‫ار‬‫ز‬‫اف‬‫و‬‫ن‬‫بدو‬‫تجزيه‬،‫سيگنال‬‫مي‬‫توان‬‫يك‬2M‫مشخص‬‫ا‬‫ر‬‫از‬‫مسير‬‫ان‬‫ر‬‫ته‬‫به‬‫از‬‫ر‬‫شي‬‫ار‬‫ر‬‫برق‬‫نمود‬.‫به‬‫اين‬‫عملكرد‬
‫اس‬‫ر‬‫ك‬‫كانكت‬Cross-Connect‫گفته‬‫مي‬‫شود‬.
51

52. 52

53.  https://en.wikipedia.org , the free encyclopedia
 http://www.huawei.com, Chinese Multinational Networking and
Telecommunications equipment and services Company
 Synchronous Transmission System (SDH)
A guide to the SDH world, ABB Switzerland Ltd.
‫اينترنت‬ ‫مقاالت‬
‫ل‬‫اصو‬ ‫با‬‫آشنايي‬SDH
‫مؤلفين‬:‫ر‬‫دهقانپو‬‫شهاب‬‫مهندس‬–‫معيني‬‫نظرعلي‬‫مهندس‬–‫فتاحي‬‫محمد‬‫مهندس‬
53