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SDH BASICS
The document discusses Synchronous Digital Hierarchy (SDH) and its advantages over Plesiochronous Digital Hierarchy (PDH). It describes some key components of SDH including section overhead bytes, path overhead bytes, virtual containers, tributary units, and administrative units. It also provides definitions and functions of various overhead bytes used for frame alignment, error monitoring, data communication, and other purposes in SDH networks.
SDH BASICS
- 1. SDH BASICS Niranjan B RegionalTelecom Training Center Mysore
- 4. DISADVANTAGES OF PDH •NO UNIVERSAL STANDARD • DIFFERENT HIERARCHIES AROUND THE WORLD • PDH NETWORK MANAGEMENT IS PROPRIETARY • DROPPING OF INDIVIDUAL CHANNELS IN HIGHER ORDER STREAM • NON-HOMOGENEITY OF EQUIPMENT • CHANNEL SEGREGATION PROBLEM • PROBLEM OF CROSS CONNECTION
- 5. S.D.H. Evolution • FibreOptic Bandwidth : • Technical Sophistication. • Intelligence :. • Customer Service Needs
- 10. SECTION OVER HEAD(SOH) •SOH bytes provide communication channels to cater for: • OA&M facilities. • user channels. • protection switching. • section performance • frame alignment • other functions.
- 12. For 1.544 MbitPDH signal (North America and Japan Standard), there are 25 bytes in 125 micro second and for 2.0408 Mbit per second signal, there are 32 bytes in 125 micro second. Taking some additional bytes for supervisory purposes, 27 bytes can be allotted for holding 1.544 Mbit per second signal, i.e. 9 rows x 3 columns. Similarly, for 2.048 Mbit per second signal, 36 bytes are allotted in 125 micro seconds, i.e. 9 rows x 4 columns. Therefore, it could be said 9 rows are matched to both hierarchies.
- 13. SDH STANDARDS STM-1 155.52Mbps SMT-4 622.08 Mbps STM-16 2588.32 Mbps 2.5G STM-64 9953.28 Mbps 10G STM-0 = 1/3rd of STM-1 51.840 Mbps Used in SONET
- 14. Synchronous Transport Module-STM •This is the information structure used to support information pay load and over head information field organised in a block frame structure which repeats every 125 micro seconds
- 15. BASIC DEFINATIONS • Container:First Entry point of PDH signal, in which signal is prepared ( adding fixed stuff, JC, Justification Opportunity byte) so that it can enter in to VC stage .32 to 34 byet fo 2Mb
- 16. MUTIPLEXING PRINCIPLE CONTAINER SIGNAL Container-n( n=1-4): A container is the information structure which forms the network synchronous information payload for a virtual container 2Mb
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- 18. BASIC DEFINATIONS • VirtualContainer(VC): • VC= Container(C) +POH (path over head) • 35 byte for 2Mb
- 19. MUX PRINCIPLE: VC-n VirtualContainer-n(VC-n):It is the information structure used to support path layer connections in the SDH. Two types of VCs: Lower order VC-n(n=1,2) Higher order Vc-n(n=3,4) CONTAINER P O H
- 20. Tributary Unit • Atributary unit is a information structure which provides adaptation between the lower order path layer and the higher order path layer. It consists of a information pay load (lower order virtual container) and a tributary unit pointer which indicates the offset of the pay load frame start relating to the higher order VC frame start. • Tributary unit 1 for VC-1 and Tributary unit 2 is for VC-2 and Tributary unit 3 is for VC-3, when it is mapped for VC-4 through tributary group-3. TU-3 pointer consists of 3 bytes out of 9 bytes. Three bytes are H1, H2, H3 and remaining bytes are fixed bytes. TU-1 pointers are one byte interleaved in the TUG-2.
- 21. CONTAINER P O H P T R MUX PRINCIPLE: TU-n/AU •It is an information structure which provides adaptation between two layers: -Between lower and higher order path layers for TU -Between higher order path layer and section layer for AU POINTER is an indicator whose value defines the frame offset of a VC with respect to the frame reference of the transport entity on which it is supported
- 22. BASIC DEFINATIONS • TributaryUnit(TU): Adaptation between lower order path and higher order path • Pointer • An indicator whose value defines frame offset of a VC with respect to the frame reference of transport entity, on which it is supported. • Administrative Unit • It is the information structure which provides adaptation between the higher order path layer and the multiplex section layer. It consists of information pay load and a A.U. pointer which indicates the offset of the pay load frame start relating to the multiplex section frame start. Two AUs are defined (i) AU-4 consisting VC-4 plus an A.U. pointer indicating phase alignment of VC-4 with respect to STM-N frame, (ii) AU-3 consisting of VC- 3 plus A.U. pointer indicating phase alignment of VC-3 with respect to STM-N frame. A.U. location is fixed with respect to STM-N frame.
- 23. BASIC DEFINATIONS • TributaryUnit(TU): Adaptation between lower order path and higher order path • Pointer • An indicator whose value defines frame offset of a VC with respect to the frame reference of transport entity, on which it is supported. • Administrative Unit • It is the information structure which provides adaptation between the higher order path layer and the multiplex section layer. It consists of information pay load and a A.U. pointer which indicates the offset of the pay load frame start relating to the multiplex section frame start. Two AUs are defined (i) AU-4 consisting VC-4 plus an A.U. pointer indicating phase alignment of VC-4 with respect to STM-N frame, (ii) AU-3 consisting of VC- 3 plus A.U. pointer indicating phase alignment of VC-3 with respect to STM-N frame. A.U. location is fixed with respect to STM-N frame.
- 24. Tributary Unit Group •One or more tributaries are contained in tributary unit group. A TUG-2 consist of homogenous assembly of identical TU-1s or TU-2. • TUG-3 consists of a homogenous assembly of TUG-2s or TU-3. • TUG-2 consists of 3 TU-12s (For 2.048 Mbit/sec). TUG-3 consists of either 7 TUG-2 or one TU-3.
- 25. BASIC DEFINATIONS • AdministrativeGroup • AUG consists of a homogenous assembly of AU-3s or an AU-4. • Concatenation • The procedure with which the multiple virtual container are associated with one another, with the result their combined capacity could be used as a single container across which bit sequence • Network Node Interface (NNI) • The interface at a network node which is used to interconnect with another network node. • integrity is maintained. •
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- 27. Embedded Overhead Bytes VC-11/12/2 POH STM-1 SOH J1 B3 C2 G1 F2 H4 F3 K3 N1 V5 J2 N2 K4 AU - PTR VC-3/4 POH A1 A1 A1 A2 A2 A2 J0 X X D1 D2 D3 B2 B2 B2 K1 K2 D4 D5 D6 D7 D8 D9 D10 D11 D12 S1 M 1 E2 X X B1 E1 F1 X X H1 Y Y H2 1 1 H3 H3 H3 Media dependent bytes X Reserved for national use SOH: Section overhead POH: Path overhead The overheads (SOH, POH) are used for maintenance and supervision of the SDH transmission network. RSOH MSOH Payload POH Pointer
- 28. Functions of RegeneratorSection Overhead Parity check (B1 calculated by regenerator and multiplexers) Data communication channels (D1...D3, F1 between regenerators) Voice communication channels (E1 between regenerators) Frame Alignment (A1, A2) Section Trace (J0 Identficationof regenerator source) A1 A1 A1 A2 A2 A2 J0 B1 E1 F1 D1 D2 D3 B2 B2 B2 K1 K2 D4 D5 D6 D7 D8 D9 D10 D11 D12 S1 M1 E2 AU - Pointer
- 29. Functions of MultiplexerSection Overhead Parity check (B2) Alarm information (K2) Remote error indication (M1,K2) Automatic protection switching (K1, K2 Bytes) Data communication channels (D4 to D12 between multiplexers) Clock source information (S1) Voice communications channels (E2 between multiplexers) A1 A1 A1 A2 A2 A2 J0 B1 E1 F1 D1 D2 D3 B2 B2 B2 K1 K2 D4 D5 D6 D7 D8 D9 D10 D11 D12 S1 M1 E2 AU - Pointer
- 30. Functions of PathOverhead V5 J2 N2 K4 J1 B3 C2 G1 F2 H4 F3 K4 N1 VC-3/4 POH VC-11/12/2 POH Parity check B3, V5/ BIP-2 calculated by path terminating point Alarm and performance information (V5, G1) Structure of the VC Signal label C2 Multiframe indication for TUs (H4) User communications channel between path elements (F2, F3) Identification of the Path Source (Path Trace J1, J2)
- 31. SOH BYTES • A-1,A-2 are framing bytes. Their values are : • A1 : 11110110 • A2 : 00101000 • These two types of bytes form 16 bit Frame Alignment Word (FAW). • FAW formed by the last A-1 byte and the adjacent A-2 byte, in the transmitter sequence defines the frame reference for each of signal rates. • There are 3 A-1 bytes in STM-1 and 3 A-2 bytes in STM-1. In higher order STM their number increases with STM order. In STM-4, there will be 12 A-1 bytes and 12 A-2 bytes.
- 32. SOH BYTES -A1,A2 • A-1, A-2 are framing bytes. Their values are : • A1 : 11110110 • A2 : 00101000 • These two types of bytes form 16 bit Frame Alignment Word (FAW). FAW formed by the last A-1 byte and the adjacent A-2 byte, in the transmitter sequence defines the frame reference for each of signal rates. There are 3 A-1 bytes in STM-1 and 3 A-2 bytes in STM-1. In higher order STM their number increases with STM order. In STM-4, there will be 12 A-1 bytes and 12 A-2 bytes.
- 33. SOH BYTES-J1/C1 • STMIdentifier with J1/ C-1 Byte : In STM-1 there is a single C-1 byte which is used to identify each of inter-leaved STM’s and in an STM-N signal. It takes binary equivalent to position in inter-leave.
- 34. SOH BYTES- D,E,F •D-1 or D-12 : These bytes are for data communication channel. In this D-1, D-2 and D-3 are for regenerator section. It can support 192 kilo bit per section. D-4 to D-12 are for multiplex section. They can support 576 kilo bit per second. • E-1 is for regenerator section order wire. • E-2 is for multiplex section order wire. • F-1 is used for fault control purposes
- 35. SOH BYTES- B1B2 • B-1 byte are called bit inter-leave parity-8. This is used for error monitoring in the regenerator section. There is only 1 byte in STM-1 or STM-4 or STM-16. On line monitoring done in this case. • B-2 bytes. These are used for error monitoring in the multiplex section. There are 3 bytes for STM-1, STM-4 and 16 will have more number of B-2 bytes as per their order.
- 36. SOH BYTES- K1K2 • K-1, K-2 bytes. • There are 2 bytes for STM-1, 4 or 16. These are used for coordinating the protection switching across a set of multiplex section organised as protection group, they are used for automatic protection switching.
- 37. Section and HighOrder Path Overhead Bytes The purpose of individual bytes is detailed below. A1,A2 Frame Alignment. B1,B2 Parity bytes for errors monitoring. D1…D3 Data communication channel (DCC) network management. D4…D12 Data communication channel (DCC) network management. E1,E2 Orderwire channel. F1 Maintenance J0 Trace identifier K1,K2 Automatic protection switching (APS) channel. M1 Transmission error acknowledgement. S1 Clock quality indicator. * Media dependent bytes.
- 41. SDH–based Transport NetworkLayered Model
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- 44. In–Service Maintenance Signals Majoralarm conditions such as Loss of Signal (LOS), Loss of Frame (LOF), Loss of Pointer (LOP) Alarm Indication Signal (AIS) to be transmitted downstream. Different AIS signals are generated depending upon which level of the maintenance hierarchy is affected
- 45. In–Service Maintenance Signals FarEnd Receive Failure (FERF) is sent upstream in the Multiplexer Section Overhead after Multiplexer Section AIS, or LOS, or LOF has been detected by equipment terminating in a Multiplexer Section span Remote Alarm Indication (RAI) for a high order path is sent upstream after Path AIS or LOP has been detected by equipment terminating a Path, and similarly, Remote Alarm Indication (RAI) for a Low Order Path is sent upstream after Low Order Path AIS or LOP has been detected by equipment terminating a Low Order Path.
- 46. S.D.H. MERITS •Simplified multiplexing/demultiplexingtechniques. •Direct access to lower speed tributaries, without need to multiplex/demultiplex the entire high speed signal. •Enhanced operations, Administration, Maintenance and provisioning capabilities. •Easy growth to higher bit rates in step with evolution of transmission technology. •Capable of transporting existing PDH signals. •Capable of transporting future broadband (ATM) channel bit rates. •Capable of operating in a multi-vendor and multi-operator environment.
- 47. ADVANTAGES OF SDH •Multi-vendor environment (mid span meet) : • Synchronous networking : • Enhanced OAM&P :. • Positioning the network for transport on new services • HUB :
Editor's Notes
- #29 A number of functions are defined in the overhead channels to ensure proper transport of the payload. The Section Overhead (SOH) The overall capacity of the SOH is 4.608 Mbit/s (9x8x64kbit/s), of which 30 bytes (1.920 Mbit/s) have fixed definitions. The remaining 64kbit/s channels are not specified. Six are reserved for national use. Although six bytes are reserved for medium dependent functions (e.g. radio link systems). The columns 1,4 and 7 corresponds also to the STS-1 frame. Functions of the SOH: Contains maintenance, monitoring and operational functions Each byte refers to a 64kbit/s channel Splitted into RSOH and MSOH Protect the connection from point of STM-1 assembly to point of disassembly. The Path Overhead (POH) The POH of VC-4/VC-3 consists of 9 bytes and the POH of the VC-11/VC-12 and VC-2 consists of 4 bytes.
- #30 The RSOH is reformed (terminated) by each regenerator. Each regenerator section passes the MSOH transparently. Section overheads (SOHs) of STM-1 are depicted by the shaded parts in the above drawing. 1.1 Regenerator SOH (RSOH), 3 rows by 9 columns, can be accessed at terminating points of a regenerator section (RS), at both regenerators and multiplexers. 1.2 Multiplex SOH (MSOH),5 rows by 9 columns, , can be accessed at multiplex section (MS) terminating points, i.e.at multiplexers only. It passes through regenerators transparently. 1.3 Information carried by RSOH and MSOH is mainly used for administration of RS and MS layer,respectively . Marked bytes are already defined. Unmarked bytes are reserved for future use. △ bytes are defined as Media-dependent. If necessary. (For SDH radio it is defined in ITU-R F.750) Bytes marked are assigned for national use. Each country can define their function differently but the definition is valid within the country, not international. Column number of STM-N is 9 x n and same byte assignment is applied but byte number of A1, A2, B2, △ and are increased accordingly. For STM-16, 64 and 256, using some of unmarked bytes FEC (Forward Error Correction) is implemented.
- #31 The MSOH is reformed (terminated) by each multiplexer and cross connect . A1, A2 : Frame Alignment Signal (FAS) 1.1 A1: 11110110 A2: 00101000 1.2 A receiver finds the STM-N frame by detecting fixed A1....A2 .... pattern which appears periodically at 125μs interval. (Remember VC-n does not have any FAS, its frame is found by using pointer.) J0 : Regenerator Section Trace 2.1 For verification of Regenerator Section connection 2.2 A transmitter can set an identifier (name) to STM-N signal, maximum 15 characters using J0, and a receiver compares the received ID (J0 value) to the expected J0 value, which is preset in the receiver, to verify the connection. 2.3 To carry 15 characters 16 multiframe is formed, the first J0 for FAS and error detection and 15 J0s for ID. 2.4 (Early recommendation defined this byte as C1 (STM identifier) that shows the unique order number of STM-1s in STM-N to assist demultiplexing process.) B1, B2 : Error Monitoring 3.1 BIP-X (Bit Interleaved Parity-X) detects error occurrence. 3.2 B1: For Regenerator Section error detection by BIP-8. B2: For Multiplex Section error detection by BIP-24N (N; STM level). Detail of BIP-X will be explained latter.
- #32 The Path Overhead is evaluated at the end point of the transmission system where the ‘unpacking’ takes place.