SdH Basics

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  • SDH BasicsGirish Jere

  • SDH BASICSWhat is SDH?Characteristics of SDHBit RatesPath and SectionSDH TRANSMISSION SYSTEM

  • What is SDH?

    A New Digital Hierarchy155.52 Mb/s, 622.08 Mb/s, 2488.32 Mb/s, 9953.28 Mb/s, 39813.120Mb/sExisting PDH and future ATM signals are carried over the SDH system.Very basic functions are same as PDH.Multiplex low bit rate digital signals to higher bit rate and transmit large information efficiently.

  • What are the differences ?Synchronous NetworkBasically, all network elements work on a single clock source.Abundant Overhead BitsTo carry large information for Network Management.Unified Interface and Multiplexing SpecificationsCommon to all countries.Standardized optical interfaces.

  • What are the benefits? (1) - Synchronous Network -Simple multiplexing processEasy access to tributary signals in a multiplexed high bit rate signal.ADD/DROPdistributionRINGsurvivabilityCROSS CONNECTcapacity managementband width managementprotection route diversity

  • What are the benefits? (2) - Overhead Bits Realization of highly advanced Network Management System for:Fault managementConfiguration managementPerformance managementSecurity managementAccounting management

  • What are benefits SDH? (3) - Unified Interface Multi-vendor EnvironmentInternational Connection

  • What are SDH? - in conclusion SDH is the infrastructure for the telecommunication network of the 21st century, providing board band and intelligent services.

  • SDH Bit Rates

  • Path and Section

  • MULTIPLEXING STRUCTURE, FRAME STRUCTURE AND POINTER Multiplexing Structure Frame Structure Pointer SDH TRANSMISSION SYSTEM

  • SDH Multiplexing Structure (1)

  • SDH Multiplexing Structure (2)

  • Multiplexing Process of SDHExample: 2 Mb/s to STM-4

  • STM-1 Frame Structure

  • Byte Interleaved Multiplex and Frame Structure STM-N STM-1 (AU-4) STM-N

  • OVERHEAD AND MAPPINGOverheadMappingSDH TRANSMISSION SYSTEM

  • STM-1 Frame Structure and SOH

  • Function of SOH (1)Framing(A1, A2)Regenerator section trace(J0)regenerator section connection check Data communication channel(D1-3)regenerator section DCC, 192 kb/s(D4-12)multiplex section DCC, 576 kb/sOrder wire(E1)accessible at regenerators(E2)accessible at multiplexersUser channel(F1)64 kb/s clear channelError monitoring(B1)regenerator sectionBIP-8(B2)multiplexer sectionBIP-24NAPS signaling(K1,2)automatic protection switching(K2)also used as MS-AIS and MS-RDISynchronization status(S1)indication of quality levelSection status reporting(M1)REI (count of BIP-24N)RDI;Remote Defect Indication(formerly FERF, Far End Receive Failure)REI;Remote Error Indication(formerly FEBE, Far End Block Error)MS;Multiplex SectionDCC;Data Communication Channel

  • Function of SOH (2)Framing(A1, A2)Regenerator section trace(J0) regenerator section connection check Data communication channel(D1-3)regenerator section DCC, 192 kb/s(D4-12)multiplex section DCC, 576 kb/sOrder wire(E1)accessible at regenerators(E2)accessible at multiplexersUser channel(F1)64 kb/s clear channelError monitoring(B1)regenerator sectionBIP-8(B2)multiplexer sectionBIP-24NAPS signaling(K1,2)automatic protection switching(K2)also used as MS-RDISynchronization status(S1)indication of quality levelSection status reporting(M1)REI (count of BIP-24N)RDI;Remote Defect Indication(formerly FERF, Far End Receive Failure)REI;Remote Error Indication(formerly FEBE, Far End Block Error)MS;Multiplex SectionDCC;Data Communication Channel

  • End-to-End Maintenance Signal

    Objectives: Given a knowledge of PDH, be able to :Describe the difference between SDH and PDHDescribe characteristics of SDHDescribe the bit rates of SDHDefine path and sectionThree different PDH (Plesiochronous Digital Hierarchy) standard for European/other countries, North American countries and Japan.ITU-T recommended a new standard common to the all countries in 1998 referred to as SDH (Synchronous Digital Hierarchy)Bit rates of transmission lines: 155.52 Mb/s 622.08 Mb/s 2488.32 Mb/s 39813.120Mb/s New technologies adopted by the SDH:4.1 Synchronous network4.2 Layered network administration structure (Section, Path, etc.)4.3 Virtual container4.4 PointerSynchronization1.1 Slave synchronization is used for synchronization distribution within a country (or a network operator).1.2 Quasi-synchronization is used between different countries (or operators), because of independent PRC (primary reference clock).Overhead data2.1 Many overhead identities are defined in detail for easy network management.Flexible multiplexing3.1 Various PDH and new services signals, both existing and future, can be carried over the SDH network.In SDH, almost direct access to a tributary signal in a line signal is possible. Step by step multiplexing/demultiplexing and stuffing/destuffing for justification , like PDH, are not required for insertion and drop of tributary signals, resulting in reduction of equipment size, power consumption, equipment and maintenance costs.This feature realized add/drop, ring system and cross connection more easily and economically than PDH.Primarily replying on optical fiber transmission networks, SDH features transmission frame with abundant spare Bytes to provide support for the speedy transfer to computer-based OAMP (Operation, Administration, Maintenance & Provisioning) information for network operators as well as highly flexible network topologies and high reliability of the network.Compatibility among manufacturers is enabled by establishing clear interface specifications.

    SDH having common world-wide formats provides realization of higher rate B-ISDN signals, such as HDTV.The basic bit rate of the transmission line is 155.52 Mb/s, with higher capacity systems based on line rates in increments of 4 times of this basic rate.STM-0 is used as a standard interface in SONET (North American SDH) and in Japan.Direct interface to SDH network of PDH 8Mb/s, 32Mb/s and 100Mb/s is not supported. But, if necessary, it is possible to carry them over SDH network by using concatenation technique. Layered network administration structure is adopted in SDH, and they are :1.1 Path1.2 Tandem Connection (TC) (optional layer)1.3 Multiplex Section (MS)1.4 Regenerator Section (RS)For administration of each layer, dedicated overhead bites are assigned.2.1 Path overhead (POH), MUX section overhead (MSOH) and 2.1 REG section overhead (RSOH). TC uses a part of POH.Regenerator section3.1 Section between adjacent repeaters or between a multiplexer and an adjacent regenerator.3.2 Or section between points where RSOH is generated and terminated.Multiplex section3.3 Section between adjacent multiplexers, may contain multiple RSs.3.4 Or section between points where MSOH is generated and terminated.When no regenerator, one physical section becomes MS and RS at the same time, but they are independent layers.Path6.1 Connection between service transmission input/output points to/from SDH network.6.2 Or connection between points where a VC is assembled and disassembled.6.3 Or connection between points where a POH is generated and terminated.Path has nothing to do with a connection route in the SDH network. Tandem Connection is a part of a path. The TC is optional and its length is determined by a network operator. Its administration is carried out using a part of POH.RS and MS are physical connection and Path and TC are logical connection.

    Objectives: Given a knowledge of SDH Basics, be able to :Describe signal names and definitions of the multiplexing steps in SDHDescribe the SDH frame structureDescribe the pointer functionDescribe the justification principle using the pointerTerms of multiplexing structure:Container (C-n) 1.1 A bandwidth packet to store PDH signals or B-ISDN signals or other services unknown yet.Virtual container (VC-n)2.1 A bandwidth packet to store signals with path overhead (POH), that carries information for Path layer administration, and is added to the container.2.2 VC-4 is named as High Order VC (HOVC) and other VCs are called Low Order VC (LOVC), because always LOVC is carried by HOVC.2.3 For SONET, VC-3 is HOVC. Concatenated virtual container (VC-4-nc)3.1 To carry high bandwidth information larger than VC-4 size, multiple VC-4s are combined into a unit.Tributary unit (TU-n)4.1 TU pointer is added to a LOVC to indicate its phase relation to HOVC, to which it is mapped.Tributary unit group (TUG-n)5.1 Multiple tributary units of the same type and speed/size are byte interleaved multiplexed into TUG-n. TUG-2 may contain TU-11 or TU-12 or TU-2.TUG-3 may contain multiple TUG-2s or a single TU-3.Administrative unit (AU-n)1.1 Phase information between a HOVC and STM-N frame (AU pointer) is added to a HOVC.AU-4 is VC-4 plus AU pointer.(for SDH)AU-3 is VC-3 plus AU pointer.(for SONET)Administrative unit group (AUG-n)2.1 Group of multiple AU-3s or AU-4s or an AU-4-nc.Synchronous transfer module (STM-N)3.1 Line or NNI(Network Node Interface) signal3.2 The AUG-ns are housed in the payload to which Regenerator and Multiplex section overhead data are added.Mapping 4.1 Process to put a service into a VC as a first step. Putting LOVCs into a HOVC via TUG is not a mapping but a multiplexing.Aligning 5.1 Pointer processing.Multiplexing 6.1 Process to combine multiple signal into a higher capacity unit using simple byte interleaved multiplexing.ETSI and SONET standard7.1 Multiplexing route via AU-4 is ETSI standard and used by most countries.7.2 Route via AU-3 is SONET standard used in North America. Japan also adopts this route.

    Multiplexing process is described from a different point of view.Except for special case, usually a PDH signal is not synchronous to a SDH signal. Frequency adjustment, i.e. justification between PDH and SDH, is necessary and carried out by stuffing bits (S) in a C-12.Stuffing bits or bytes other than for the justification are also inserted in order to get neat size harmonization with other level packets during mapping and multiplexing. This kind of stuffing bytes are used in every step. The drawing shows multiplex concept. Actual process is not packet level multiplex but byte interleaved multiplex, i.e. neighbor byte belongs to other packet.In this process, AUG-1 is the same as the AU-4.A STM-1 frame cycle is 125 s and contains 2,430 bytes.1.1 In the SDH, vertical and horizontal matrixes represent a frame structure. Vertical matrixes are always nine rows. 1.2 The number of horizontal matrixes depends on the bit rate (from STM-1 to STM-N). 1.3 Transmission order is row by row and left to right. For STM-1, the matrixes are nine rows by 270 columns. (Segments represent the conventional frame structure.)In this matrix representation, overheads are arranged on the left end.3.1 The number of overheads is nine rows by nine columns.3.2 The first to third rows are the Regenerator section overhead data.3.3 The fourth row is the AU pointer.3.4 The fifth to ninth rows are the Multiplex section overhead.The remaining portion supports the traffic, referred to as a payload.Byte Interleaved Multiplex1.1 SOHs of all STM-1s are terminated (as a result they turn into AU-4).1.2 Phase of AU-4s are aligned and all AU pointers are renewed (detail will be explained later).1.3 1st byte of 1st AU-4 (A) is put to 1st byte of AUG-n, 1st byte of 2nd AU-4 (B) to 2nd byte of AUG-n, ......., 1st byte of (n)th AU-4 (N) to (n)th byte of AUG-4.1.4 2nd byte of 1st AU-4 (A) is put to (n+1)th of AUG-n, 2nd byte of 2nd AU-4 (B) to (n+2)th byte of AUG-n, ......., 2nd byte of (n)th AU-4 (N) to (2n)th byte of AUG-41.5 ...............1.6 Pointers of AU-4s are also byte interleaved multiplexed into 4th row and 1st to 9th column, indicated as AU PTRs.1.7 Insert a new STM-N SOH.STM-n Frame2.1 Number of row remains 9. Nine rows rule is common to all packet.2.2 Column number for SOH and AU pointers is 9 x n and columns for payload are 261 x n.2.3 Frame period is 125 micro seconds.Objectives: Given a knowledge of SDH Basic, be able to :Layout and describe the purposes of RSOH, MSOH, and POHDescribe mapping of tributary signals to NNISection 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.A1, A2 : Frame Alignment Signal (FAS)1.1 A1: 11110110 A2: 001010001.2 A receiver finds the STM-N frame by detecting fixed A1....A2 .... pattern which appears periodically at 125s interval. (Remember VC-n does not have any FAS, its frame is found by using pointer.)J0 : Regenerator Section Trace2.1 For verification of Regenerator Section connection2.2 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 Monitoring3.1 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.E1, E2 : Engineering OrderwireOne byte in STM-n frame makes a 64 kb/s data channel. Digitized (PCM) voice of an engineering orderwire is carried by E1 and/or E2.1.1 E1 can be accessed from both multiplexer and regenerators.1.2 E2 can be accessed only from the multiplexer.F1 : User Channel A network operator can use the F1 user channel (64 kb/s clear channel) for its own purpose. D1-3, D4-12 : Data Communication Channels (DCC) Both D1-3 (192 kb/s) of the RSOH and D4-12 (576 kb/s) of the MSOH are used for data communication channels. 3.1 They are often called DCCr and DCCm, r and m means RS and MS. DCCr is recommended for OAMP information transmission (NMS connection). 3.2 DCCm is a kind of an user accessible channel and its purpose is not limited to NMS connection.K1, K2 : Automatic Protection Switching (APS) Signaling4.1 Used to exchange control information among nodes in an MS-SP Ring (BLSR) and a line-protection linear systems.4.2 Some bits in K2 are used as a Multiplex Section Remote Defect Indication (MS-RDI) that indicates detection of defect in the receiving section or reception of MS-AIS. S1 : Synchronization Status5.1 S1 shows the quality level of the clock source that generated the STM-n frame. 5.2 It is used to control network synchronization, i.e. for selection of a reference clock source.M1 : Multiplex Section Remote Error Indication (MS-REI)6.1 M1 is used to report a result of error detection by B2, by number of BIP violation = error count, back to the transmission source.6.2 For STM-64 and 256 two bytes (M0 and M1) are assigned.Z1, Z2 : (Spare Bytes) STM-N (N>4) has additional spare bytes (Z0).A remote station alarm is a report of signal receiving status back to the transmission source.Maintenance signals of SDH system consist of AIS, RDI and REI.AIS (Alarm Indication Signal)3.1 Reports signal failure in the upper stream of the signal flow to the down stream, indicating you are receiving defective signal but its not your fault. It is generated when LOF (Loss of framing), LOS (Loss of signal), LOP (Loss of pointer), AIS, EBER (Excessive bit error, optional), etc. are detected.RDI (Remote Defect Indication)4.1 Reports detection of received signal failure to the transmitting side, under the same condition as AIS.REI (Remote Error Indication)5.1 Reports error count detected by BIP-X to the transmitting side (for LOVC, only error presence).RFI (Remote Failure Indication)6.1 reports declaration of failure (persistence of failure beyond threshold) to the transmission side. This is defined only for VC-11.