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S-108.199 OPTICAL COMMUNICATIONS AND INSTRUMENTS SDH and WDM, 10.3.2004 Antti Pietiläinen 1 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi How the future of layering looked 4 years ago Transport/Application Layer IP Trend towards simplification of protocol stacks From this Towards this FR ATM PDH SDH Transport IP ATM IP Digital Signal (FR, FOTS, PDH) WDM/Optical Networking Layer Time Current Systems 2 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi Current R&D Future Deployment (3-6 yrs) How the future looks now From this Transport/Application Layer IP Trend towards simplification of protocol stacks Towards this FR ATM PDH IP GFP SDH Transport Ethernet IP GFP OTN Current Systems 3 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi OTN Current R&D and future deplyment Acronyms of previous page • IP = Internet protocol • FR = frame relay • PDH = plesiochronous digital hierarchy • ATM = asynchronous transfer mode • SDH = synchronous digital hierarchy • GFP = generic framing procedure • WDM = wavelength division multiplexing • OTN = optical transport network 4 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi Digital signal • Analog telephone connection carries the frequencies between 300 Hz and 3400 Hz. • The signal can be converted into a digital signal by sampling 8-bit samples at 8000 samples/s. • Channels are multiplexed together using time domain multiplexing. Each channel gets one-byte timeslot in every frame. Frame rate is 8000 frames per second. 30 or 31 channels fit into 32 time slots where one or two time slots are used for frame alignment and signaling. The total bit rate of E1 frame is 2.048 Mbit/s. • The ANSI frame T1 includes 24 64-kbit/s channels. A single frame has 24 x 8 =192 payload bits and one framing bit. • The 64-kbit/s channels collected into one E1 or T1 are digitized using the same clock. Thus, the channels are synchronized with each other. Ramaswami has assumed the framing bit as a stuffing bit, which could accommodate bit rate differences, so p. 365 has an error. • However, individual E1 and T1 signals are not necessarily synchronized with each other. 5 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi Short history multiplexing hierarchy, PDH • PDH – plesiochronous digital hierarchy. Multiplexing signals, which are running at almost the same speed. • First standards in the second half of 1960s. • Tributaries and higher order bit streams are allowed to deviate from a pre-defined bit rate by a specified amount, for example at 2 Mbit/s the value is 50 ppm. • Justification (bit stuffing) process is therefore required, which brings all the tributaries up to the same bit rate before multiplexing takes place. 6 © NOKIA Level North America Europe Japan 0 DS or T 0.064 Mbit/s E 0.064 Mbit/s 0.064 Mbit/s 1 1544 Mbit/s 2048 Mbit/s 1544 Mbit/s 2 3 4 6312 Mbit/s 44736 Mbit/s 139264 Mbit/s 8448 Mbit/s 34368 Mbit/s 139264 Mbit/s 6312 Mbit/s 32064 Mbit/s 97728 Mbit/s S_108_199_10_3_2004.ppt / 10.3.2004 / APi PDH multiplexer mountain • When a signal is demultiplexed, the stuffed bits are removed. Each level knows how to demultiplex the next level. • To extract a 2-Mbit/s signal from a high- bit rate stream, a “multiplexer mountain” is required. 34 Mbit/s 140 Mbit/s 34 140 MUX 832 MUX 8 Mbit/s 28 MUX 2 Mbit/s Drop/Add 7 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi 2 Mbit/s 28 MUX 34 - 140 Mbit/s 140 MUX 832 MUX Foundation of SDH/SONET • Developed during late 1980s • SDH - Synchronous digital hierarchy (Europe, Japan, Intercontinental cables, ITU recommendation) • SONET – Synchronous optical network (North America, ANSI standard) • All clocks in a network are synchronized to a single master clock. • All bit rates are integer multiples of the basic bit rates and no bit stuffing is required. • A lower bit rate stream can be extracted from a multiplexed SONET/SDH stream in a single step. 8 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi Other advantages of SONET/SDH • Management • Incorporates extensive management information for managing the network • Performance monitoring • Identification of connectivity and traffic type • Identification and reporting of failures • Data communication channel • Interoperability • PDH standard did not specify standard format on the transmission link. Therefore different vendors used different line coding, optical interfaces etc. In SDH standardization is more complete. However, there are still some problems in connecting equipment from different vendors • Network availability • Incorporate specific network topologies and specific protection techniques and associated protocols to provide high availability. Restoration time after failure can be less than 60 ms. 9 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi Multiplexing • The basic SONET bit rate is 51840 Mbit/s and the basic SDH bit rate is 155.420 Mbit/s. The highest bit rate standardized so far is 39813.120 Mbit/s. Optical Level Electrical Level Line Rate (Mbps) SDH Equivalent OC-1 (ANSI) STS-1 Payload Overhead Rate (Mbps) Rate (Mbps) 51.840 50.112 1.728 - OC-3 STS-3 155.520 150.336 5.184 STM-1 OC-12 STS-12 622.080 601.344 20.736 STM-4 OC-48 STS-48 2488.320 2405.376 82.944 STM-16 OC-192 STS-192 9953.280 9621.504 331.776 STM-64 OC-768 STS-768 39813.120 38486.016 1327.104 STM-256 (ANSI) 10 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi SDH Multiplexing structure (ITU-T G.707) x1 x1 AUG-4-256c STM-256 AUG-256 STM-64 STM-16 STM-4 STM-1 STM-0 x1 x1 x1 x4 x1 AUG-64 x4 AUG-16 x4 AUG-4 x1 AUG-1 AU-4 SONET Pointer processing Multiplexing Aligning Mapping AU-3 C-4-64c 2396.16M C-4-16c 599.04M VC-4-4c C-4-4c 150.336M VC-4 149.8M x3 x 1 ETSI ETSI ETSI TUG-3 SONET x 3 x1 9584.64M VC-4-16c AUG-4-4c x1 C-4-256c VC-4-64c AUG-4-16c x4 x1 VC-4-256c AUG-4-64c x1 38338.56M VC-3 SONET TU-3 ETSI x 7 x1 x7 TUG-2 SONET x4 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi DS4 139M E4 139M C-3 DS3 45M E3 34M C-2 DS2 6M SONET TU-2 x3 VC-2 TU-12 VC-12 C-12 E1 2M TU-11 VC-11 C-11 DS1 1.5M ETSI SONET 11 ETSI VC-3 C-4 Procedures in SDH framing • SDH mapping: A procedure by which tributaries are adapted into Virtual Containers at the boundary of an SDH network. • SDH multiplexing: A procedure by which multiple lower order path layer signals are adapted into a higher order path or the multiple higher order path layer signals are adapted into a multiplex section. • SDH aligning: A procedure by which the frame offset information is incorporated into the Tributary Unit or the Administrative Unit when adapting to the frame reference of the supporting layer. 12 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi Cross-connecting VCs • VCs arrive inside STMs into a cross connect. The VCs are recovered and cross-connected to another port and aligned into another STMs. Connection points In 1 STM-1 1 In 2 STM-4 1 flexible matrix Connection points 1 2 2 3 4 3 4 1 STM-4 Out 1 STM-1 Out 2 VC-4 pipes : continuous stream of virtual containers 13 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi Aligning virtual containers into TU (transport unit) or AU (administrative unit) • Virtual container is a frame (frame rate 8000 frames/s). • The virtual containers are synchronous because the clock is derived from the master clock of the network. • However, virtual containers may travel a long way and go through many links. • Each link transmits frames between two nodes at a frame rate of 8000 frames/s. The bit rate of all consecutive links may be the same but the frame boundaries occur at different moments. Thus, VCs float inside the TUs or AUs and a pointer indicates where the starting point of a VC is within a TU or AU 14 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi Pointer TU-12 frame VC-12 frame Pointer TU-12 frame Justification bytes and pointer slip • Sometimes the whole network is not synchronized and VCs may be running at a slightly faster or slower rate than the TU or AU. • Therefore the pointer must slip one byte every now and then. For allowing slightly faster rate there has to be an extra byte in the TU or AU that may take the last byte of a frame when there is a negative slip where the VC shifts to a location one byte earlier than before and would otherwise overwrite a byte. Correspondingly, in the case of positive split, one byte in the TU or AU is jumped over and left empty. 15 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi Building an STM-1 from E2s STM-1 Multiplex x1 + MSOH, 2.88 Mbit/s, and RSOH, 1.728 Mbit/s AUG-1 Multiplex x1 AU-4 Alignment of VC-4 into AU-4 and add AU pointer + 3 justification bytes VC-4 Multiplex x3 + add VC-4 POH, 576 kbit/s (higher order VC POH) TUG-3 TUG-2 TU-12 Multiplex x7 Multiplex x3 Alignment of VC-12 into TU-12 and add 2-byte TU pointer+justification byte + one empty byte for every 4 frames, 64 kbit/s VC-12 POH, 64 kbit/s VC-12 Add (lower order VC POH) C-12 Add stuffing bits, 128 kbit/s 2.048 Mbit/s tributary signal in 16 © NOKIA STM = Synchronous transfer module MSOH = Multiplexer section overhead RSOH = Regenerator section overhead AUG = Administrative unit group AU = Administrative unit TUG = Tributary unit group TU = Tributary unit POH = Path overhead VC = Virtual container C = Container S_108_199_10_3_2004.ppt / 10.3.2004 / APi Mapping Moving pointer in a cross connect Pointer Pointer TU-12 frame TU-12 frame VC-12 frame TU-12 frame Multiplex section n 17 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi Pointer TU-12 frame VC-12 frame Multiplex section n + 1 Recovering an E2 from an STM-1 STM = Synchronous transfer module MSOH = Multiplexer section overhead RSOH = Regenerator section overhead AUG = Administrative unit group AU = Administrative unit TUG = Tributary unit group TU = Tributary unit POH = Path overhead VC = Virtual container C = Container STM-1 Demultiplex ÷ 1, read MSOH and RSOH AUG-1 Demultiplex ÷ 1 Recovery of VC-4 from AU-4 AU-4 (read AU pointer + strip justification bytes) VC-4 TUG-3 TUG-2 Demultiplex ÷3 read VC-4 POH Demultiplex ÷7 Demultiplex ÷ 3 of VC-12 from TU-12 TU-12 Recovery (read TU pointer + strip justification byte VC-12 Read VC-12 POH C-12 Remove stuffing bits 2.048 Mbit/s tributary signal out 18 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi SDH sublayers (VC) path Path Multiplexer section Line Regenerator section Terminal multiplexer SONET: Section Regenerator Tributaries Add/drop multiplexer Terminal multiplexer Tributaries •Path, Multiplexer section and Regenerator section each carry management information, which is terminated at the endpoints of the path or section. 19 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi STM-1 frame • The resulting STM-1 frame 1 2 3 1 2 3 4 4 5 6 7 AU pointers 125 µs Multiplex section overhead 8 9 20 © NOKIA 270 bytes Regenerator section overhead 5 6 7 8 9 10 S_108_199_10_3_2004.ppt / 10.3.2004 / APi SDH physical interface example • V-16.2 STM-16, 2.5 G 1550 nm • Fiber type G.652 standard single-mode fiber • Loss 22-33 dB • Allowed dispersion 2400 ps/nm • Fiber has attenuation of <0.275 dB/km and dispersion 17 ps/nm/km 21 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi Optical communications cumulative market size Cumulative Market size • The hype reached its peak in 2000 • Current estimates indicate solid but lower growth Access wave Estimate 2000 Metro wave Core wave Estimate 2004 1990 22 © NOKIA 1995 S_108_199_10_3_2004.ppt / 10.3.2004 / APi 2000 2005 2010 Laboratory experiments conquering dispersion limits • Chromatic dispersion limit using standard single-mode fiber: 2.5 Gbit/s 1000 km, 10 Gbit/s - 60 km. Most fiber laid in the ground is standard single mode fiber. • 1 Terabit/s (100 × 10 Gbit/s) transmission over 7300 km non-zero dispersion shifted fiber, Electronics Lett. 35 (1999) p.2212. • 1.28 Tbit/s (32 x 40 Gbit/s) over 1000 km non-dispersion-shifted fiber using dispersion compensation fiber, Electronics Lett. 37 (2001) p.43. • DWDM 40 x 40G transmission over trans-Pacific distance (10,000 km) using CSRZ-DPSK, enhanced FEC and all-Raman amplified 100 km UltraWave™ fiber spans,” Technical Digest of OFC 2003, post-deadline paper, PD18, (2003). 23 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi WDM layer below SDH layer • WDM has introduced functionality, such as optical add/drop multiplexers and optical regeneration below SDH in layered model. • Optical transport network (OTN) layer serves SDH client layer. Path LAYER TDM Electrical Layers Multiplex Section LAYER Regenerator Section LAYER Optical Channel LAYER WDM Optical Layers Optical Multiplex Section LAYER Optical Transmission Section LAYER Fibre LAYER 24 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi Optical sections within a single SDH regeneration section OPTICAL MULTIPLEX SECTION OPTICAL MULTIPLEX SECTION OPTICAL OPTICAL OPTICAL TRANSMISSION TRANSMISSION TRANSMISSION SECTION SECTION SECTION TRIBUTARY SIGNALS TRIBUTARY SIGNALS WDM MULTIPLEXER OPTICAL AMPLIFIER OPTICAL AMPLIFIER OPTICAL CROSS-CONNECT Optical Channel SDH REGENERATOR SECTION 25 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi WDM DEMULTIPLEXER Optical channel frame • STM-16 + FEC = OTU1, STM-64 + FEC = OTU2, STM-256 + FEC = OTU3 • Other payload mappings available, for example Generic framing procedure. OTU type OTU nominal bit rate OTU1 255/238 × 2 488 320 kbit/s OTU2 255/237 × 9 953 280 kbit/s OTU3 255/236 × 39 813 120 kbit/s OTU bit rate tolerance ±20 ppm NOTE – The nominal OTUk rates are approximately: 2 666 057.143 kbit/s (OTU1), 10 709 225.316 kbit/s (OTU2) and 43 018 413.559 kbit/s (OTU3). OTU = Optical channel transport unit, FEC = Forward error correction Source ITU-T G.709 (03/2003) 26 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi Optical transport network functionality • Service provisioning • Protection • Performance monitoring • Wavelength conversion • Multiplexing and grooming • Bit rate transparency (with provisions) • High bit rate more sensitive to dispersion and attenuation • Very high bit rate consumes more optical bandwidth 27 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi WDM network elements • Optical add/drop multiplexers (OADM) Ring network 28 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi Linear network WDM network elements • Optical crossconnects (OXC) OXC OADM Mesh OADM OXC 29 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi OADM Protection at different optical layers OXC • Optical channel protection • A backup route is planned for a path • Optical multiplex section protection • A link between two OXCs has a backup route. OADM OADM OXC OADM Trail Protection 1+1 1:1 m:n Optical Transmission Section Layer 30 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi 1+1 1:1 (end-to-end trail, ffs) Optical Channel Layer Optical Multiplex Section Layer Subnetwork Protection (meshed networks) (ring protection) (ring protection) (meshed networks) m:n (section) (ring protection) (ring protection) OADM architectures • Parallel where all the wavelengths are separated and multiplexed back λw λ1, λ2, …, λw λ2 λ1 Drop 31 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi λ1, λ2, …, λw λ2 λ1 Add OADM architectures • Modular version of parallel architecture Band 4 λ1, λ2, …, λw λ1, λ2, …, λw Band 3 Band 2 Band 1 λ1 λ2 Drop 32 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi Add OADM architectures • Serial λ1, λ2, …, λw Drop λ1, λ2, …, λw λ1 Add λ2 λ3 • Band drop λ1, λ2, …, λw λ1, λ2, …, λw Drop Add λ1, λ2, λ3 33 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi OADM architectures • Reconfigurable parallel architecture Optical switch λ1, λ2, …, λN λ1, λ2, …, λN λN 34 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi λ2 λ1 Optical crossconnect (OXC) OLT (optical line terminal) OXC 35 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi Different scenarios for OXC deployment OLT (optical line terminal) • Electrical switch core O E O O E O O E O E E O E O O E O O E O O E O O E O O E O E E O E O O E O O E O Electrical core • Optical switch core surrounded by O/E/O converters 36 © NOKIA O E O O E O O E O O E O O E O O E O O E O O E O O E O O E O O E O O E O O E O O E O O E O O E O S_108_199_10_3_2004.ppt / 10.3.2004 / APi Optical core Different scenarios for OXC deployment • Optical switch core connected directly to transponders in OLT O E O O E O O E O O E O Optical core O E O O E O OLT O E O O E O • Optical switch core directly connected to multiplexer in OLT OLT Optical core 37 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi Optical core wavelength plane OXC λ1, λ2, λ3 λ1 λ1, λ2, λ3 λ2 λ1, λ2, λ3 λ1, λ2, λ3 Local add Local drop λ1 38 © NOKIA λ2 S_108_199_10_3_2004.ppt / 10.3.2004 / APi λ3 λ3 λ2 λ1 Reading instructions • SDH, pp. 364-381. SDH multiplexing hierarchy instead of SONET multiplexing hierarchy. • WDM, pp. 403-430 and optical network layering and the principle of optical protection. 39 © NOKIA S_108_199_10_3_2004.ppt / 10.3.2004 / APi