1 / 87

Chapter 8

Chapter 8. Digital Transmission Systems Part 2. 10 SDH and SONET. SDH is an acronym for Synchronous Digital Hierarchy . It is an European development .

dior
Télécharger la présentation

Chapter 8

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Chapter 8 Digital Transmission Systems Part 2 Bahman R. Alyaei

  2. 10 SDH and SONET • SDH is an acronym for Synchronous Digital Hierarchy. It is an European development. • SDH: is a hierarchical set of digital transport structures (Overhead), standardized for the transport of suitably adapted Payloads over physical transmission networks. • SONET is an acronym for Synchronous Optical Network . It is a North American development. • The two (SDH and SONET) are very similar. Bahman R. Alyaei

  3. Continue… Bahman R. Alyaei

  4. Continue… • Either one can accommodate the standard E1 family (i.e., 2.048 Mbps, etc.) and DS1family (i.e., 1.544 Mbps, etc.) of line rates. • SDH/SONET is replacing PDH systems in the Transport Network. • By Transport Network we mean the flexible high-capacity transmission network that is used to carry all types of information. • By Flexible we mean that telecommunications operators are able to easily modify the structure of the transport network from the centralized management system. Bahman R. Alyaei

  5. 10.1 Advantages of SDH/SONET • SDH/SONET is based on the principal of direct synchronous multiplexing, where separate, slower signals can be multiplexed directly onto higher speed SDH/SONET signals without intermediate stages of multiplexing. • SDH/SONET is more flexible and reliable than PDH and provides advanced network management and maintenance features. Bahman R. Alyaei

  6. Continue… • Can be used in Long-Haul Networks, Local Networks and Loop Carriers, and it can also be used to carry CATVvideo traffic, ATM, and ISDN. • In SDH/SONET format, only those channels that are required at a particular point are demultiplexed, thereby eliminating the need for back-to-back multiplexing. In other words, SDH/SONET makes individual channels “visible” and they can easily be added and dropped. Bahman R. Alyaei

  7. Continue… • The data rates for optical transmission are standardized (i.e., vendor independent). • Different systems are included in standards, for example, Terminal, Add/Drop, and Cross-Connection Systems. • These systems make SDH/SONET networks more flexible than PDH systems, which include only terminal multiplexer functionality. Bahman R. Alyaei

  8. 10.2 Why SDH/SONET • Originally, all communications in the telephone network was analog. • Analog lines or analog microwave links were used to connect to switching offices. Bahman R. Alyaei

  9. Continue… • In about 1962, the network providers began using digital communications between switching centers. • This was PDH system (DS-Carrierin US and E-Carrierin Europe). Bahman R. Alyaei

  10. E1 or DS1 E1 or DS1 Continue… • As communications needs grew, many DS-Carrier or E-Carrier lines were needed between switching centers. • In the late 1970’s optical communications began to be used to interconnect switching offices. Bahman R. Alyaei

  11. Continue… • Prior to standardization, every manufacturer of optical communications used their own framing. • The ANSI and the ITU began work in 1986 to define standards for optical communications. • Both bodies finalized their first set of standards in 1988. Bahman R. Alyaei

  12. Continue… • They defined the following: • Optical and Cupper interfaces (wavelength, frequency, power, etc.). • Rates, frame formats, and network elements (Layers). • Operations, Administration, and Maintenance (OAM) functions including monitoring for valid signal, defect reporting, and alarms due to abundant overhead bits. Bahman R. Alyaei

  13. 10.3 Basic SDH/SONET Transmission Rates (Hierarchy) • SONET and SDH converge at SDH’s 155 Mbps base level, defined as STM-1 (Synchronous Transport Module-1). • The base level for SONET is STS-1 (Synchronous Transport Signal-1) or OC-1 (Optical Carrier-1) and is equivalent to 51.84 Mbps. • Thus, SDH’s STM-1 is equivalent to SONET’sSTS-3 (3 x 51.84 Mbps = 155.52 Mbps). • Higher SDH rates of STM-4 (622 Mbps), STM-16 (2.4 Gbps), and STM-64 (10 Gbps) have also been defined. Bahman R. Alyaei

  14. Bahman R. Alyaei

  15. Continue… Data Rates of SONET and Corresponding SDH Data Streams Bahman R. Alyaei

  16. Continue… • Multiplexing is accomplished by combining or interleaving multiple lower-order signals (1.5 MbpsDS1 carrier, 2 Mbps E1 carrier, etc.) into higher-speed circuits (51 Mbps STS-1, 155 Mbps STM-1, etc.). • By changing the SONET standard from Bit- Interleaving to Byte-Interleaving, it became possible for SDH to accommodate both transmission hierarchies. • This modification allows an STM-1signal to carry multiple 1.5 Mbps or 2 Mbps signals and multiple STM signals to be aggregated to carry higher orders of SONET or SDH tributaries. Bahman R. Alyaei

  17. 11 SDH STM Signal • SDH multiplexing combines low-speed digital signals such as 2, 34, and 140 Mbps signals with required Overhead to form a frame called STM-1. • SDH is a Byte-Interleaving multiplexing system. • An STM is the information structure used to support Section Layer Connections in the SDH. Bahman R. Alyaei

  18. Continue… • It consists of information Payload and Overhead (OH) information fields organized in a block frame structure which repeats every 125 μS. • The information is suitably conditioned for serial transmission on the selected media at a rate which is synchronized to the network. • STM-1 is the base level of SDH. Bahman R. Alyaei

  19. Continue… • The STM-1 frame, is created by 9 segments of 270 bytes each (1-byte = 8-bits) • The first 9 bytes of each segment carry Overhead (OH) information. • The remaining 261 bytes carry Payload. • When visualized as a block, the STM-1 frame appears as 9 rows by 270 columns of bytes. • The STM-1 frame is transmitted row-by-row. • Row #1 first, with the most significant bit (MSB) of each byte transmitted first, then the Row #2 and so on, up to Row #9. Bahman R. Alyaei

  20. Continue… • The STM-1 frame lasts for 125 μS, in other words, the 9 row segments will be transmitted in a total time equal to 125 μS. • This will permit SDH to easily integrate existing digital services into its hierarchy. • Therefore, there are 8000 frames per second. Bahman R. Alyaei

  21. Segment no. 7 270 Bytes in (125/9) μS The STM-1 frame Bahman R. Alyaei

  22. STM-1 frame visualized as a block, and the direction of transmission Bahman R. Alyaei

  23. Continue… Bahman R. Alyaei

  24. STM-1 frame visualized as a block Bahman R. Alyaei

  25. Continue… • Hence, the STM-1 frame rateRf is Rf = 8000 frames per second • The bit rate Rb of STM-1 frame is calculated as follow: Rb = Rf x Cf , where Rfis the frame rate (frames/second). Cf is the frame capacity (bits/frame). • The frame capacity of a signal is the number of bits contained within a single frame. Bahman R. Alyaei

  26. Continue… • We know that the frame rate is Rf = 8000 frames/second. • Cfis calculated as follow Cf = 270 bytes/row x 9 rows/frame x 8 bits/byte = 19,440 bits/frame • Then, the bit rate Rb of the STM-1 signal is calculated as follows: Rb = 8000 frames/second x 19,440 bits/frame = 155.52 Mbps Bahman R. Alyaei

  27. Continue… • The multiplexing of multiple data stream, plays an important role in SDH. • Byte Interleaving scheme is used to multiplex multiple data stream. • The higher transmission levels (Multiplex) such as STM-4 and STM-16 of the SDH Hierarchy are generated from integer multiples of STM-1 signal. • In general, STM-N signal is generated by Byte InterleavingN STM-1signal. Bahman R. Alyaei

  28. Continue… Multiplexing of STM-1 to generate STM-N Bahman R. Alyaei

  29. Continue… STM-N signal frame structure Bahman R. Alyaei

  30. Continue… • Example: • An STM-4 signal will be created by Byte Interleavingfour STM-1 signals. • The basic frame rate remains 8,000 frames per second, but the capacity is quadrupled, resulting in a bit rate of 4 x 155.52 Mbps or 622.08 Mbps. Bahman R. Alyaei

  31. Continue… Multiplexing of STM-1 to generate STM-4 Bahman R. Alyaei

  32. 11.1 SDH STM-1 Frame Structure • As we know that, the SDH frameSTM-1 consists of two parts: • The FirstNine Columns comprise the Overhead (OH), occurs at a rate 9 x 9 x 8 x 8000 = 5.184 Mbps. • While the remainder is called the Payload, which is also called Virtual Container (VC), occurs at a rate 9 x 261 x 8 x 8000 = 150.336 Mbps. Bahman R. Alyaei

  33. Continue… • The OH is further divided into: • Section Overhead (SOH). • Administrative Unit Pointer (AU-PTR). • The Payload or Virtual Container (VC) is further divided into: • Path Overhead (POH): One column. • Container (C): 260 columns and data rate given by 9 x 260 x 8 x 8000 =149.76 Mbps. Bahman R. Alyaei

  34. 125 μS 1 9 10 11 270 1 3 SOH Container 4 9 rows AU-PTR SOH POH 9 9 columns Overhead (OH) 271 columns Virtual Container (VC) SDH frame STM-1 structure Bahman R. Alyaei

  35. Continue… • The SOH dedicates • Three Rows for the Regenerator Section Overhead (RSOH) and • Six Rows for the Multiplexer Section Overhead (MSOH). • Rate of RSOH and MSOH is given by RSOH = 3 x 9 x 8 x 8000 = 1.728 Mbps. MSOH = 6 x 9 x 8 x 8000 = 3.456 Mbps. Bahman R. Alyaei

  36. 125 μS 1 9 10 11 270 1 3 RSOH Container 4 9 rows AU-PTR MSOH POH 9 9 columns Overhead (OH) 261 columns Virtual Container (VC) SDH frame STM-1 structure Bahman R. Alyaei

  37. 11.2 The Truck Analogy • SDH frame functions as a transport truck which has a tractor and a container type trailer. • It packs the signals of different hierarchies into packages of different sizes like packing cargoes and then loads them into the truck. Bahman R. Alyaei

  38. Continue… • The contents carrier in the container are real goods. • These are analogous to customer traffic, being carried in the Payload area of SDH frame. SDH frame Bahman R. Alyaei

  39. 11.3 The Function of OHs • The OH within the SDH signal supports network management at both the Path and Section levels. • To realize layered monitoring, the OH is classified into SOH and POH. • SOH and which includes RSOH and MSOH, is responsible for the section layer OAM. Bahman R. Alyaei

  40. Continue… • SOH functions are: • Frame alignment pattern. • Parity check. • STM-1 identification. • Alarm information. • Automatic protection switching. • Data communication channel. • Voice communication channel. • User channel. Bahman R. Alyaei

  41. Continue… • The POH is responsible for the Path layer OAM functions. Bahman R. Alyaei

  42. 11.4 Function of The Pointer • SDH network is intended to be synchronous network. • However, there will always be slight timing differences because different clocks are being used or the same clock is being distributed over long distances. • SDHPointers allow this limited asynchronous operation within the synchronous network. • It points the location of the VC in the STM frame. Bahman R. Alyaei

  43. 12 SDH Signal Hierarchy Typical SDH Communication Network Bahman R. Alyaei

  44. Continue… • There are three Sections in the SDH signal hierarchy: • Path. • Multiplex Section. • Regenerator Section. • The Overheads (OHs) are always generated at the beginning of a section and only evaluated at the end of a section. Bahman R. Alyaei

  45. Continue… The SDH Layer Model Bahman R. Alyaei

  46. 12.1 SDH Network Elements • The SDHsignal is layered to divide responsibility for transporting the Payload through the network. • Each SDHNetwork Element (NE) is responsible for • Interpreting and generating its overhead layer, • Communicating control and status information to the same layer in other equipment, • Terminating its overhead layer. Bahman R. Alyaei

  47. Continue… • As the Payload travels through the SDH network, each layer is terminated by one of a general class of NEs named • Regenerator Section Terminating Equipment (RSTE), • Multiplexer Section Terminating Equipment (MSTE), • Path Terminating Equipment (PTE). Bahman R. Alyaei

  48. 12.1.1 Path Terminating Equipment (PTE) • PTE is an entry-level path-terminating terminal multiplexer, acts as a concentrator of E1s as well as other tributary signals. Terminal multiplexer example Bahman R. Alyaei

  49. Continue… • PTE is a terminating multiplexer. • It is responsible for adding first order POH, RSOH,and MSOH to the data Container (C). • Its simplest deployment would involve two terminal multiplexers linked by fiber with or without a regenerator in the link. • This implementation represents the simplest SDH link (Regenerator Section, Multiplex Section, and Path, all in one link). Bahman R. Alyaei

  50. 11.1.2 Regenerator • A regenerator is needed when, due to the long distance between multiplexers, the signal level in the fiber becomes too low. Regenerator. Bahman R. Alyaei

More Related