The Synchronous Digital Hierarchy (SDH) Part I

The Synchronous Digital Hierarchy (SDH) - I part by JM Caballero © Trend Communications PDH limitations • the multiplexing is bit oriented (second, third and fourth hierarchy) it is not possible to execute direct add&drop of low speed tributaries poor monitoring capacity because computers are byte oriented lack of management standards and short space to implement them (S bits) lack of standardization between Japan, USA and rest of the world lack of optic standards just proprietary solutions no mechanisms to manage the quality, just for 2Mbit/s with CRC4 • • • • • • © Trend Communications 2/ 63 Causes to define SDH • The Antitrust law at US followed by Bell break into small companies. Was necessary to interconnect new PTT´s: SONET definition B-ISDN specification to integrate any traffic: SDH and ATM standardization Advanced management needs: computers and telecom must work together Requirement for having new infrastructures to fit any traffic: data, voice, multimedia • • • • © Trend Communications 3/ 63 bytes vs. bits frame 1 125 µ s 0 1 byte n 0 frame 2 125 µ s rate = 8 bits 125·10-6seg. = 64Kbit/s Standardize since 1988 when appeared the G707, G708, G709 CCITT recommendations • • • SDH is byte oriented, it means that a byte is the unit for mapping and multiplexing STM-N is the name for the transport frames. They have always a period of 125µs An important consequence is that in SDH 1 byte represents a 64 Kbit/s channel © Trend Communications 4/ 63 SDH objectives (i) • • • • direct internetworking between equipments scalability in transmission speeds until 0 Gbit/s direct add&drop for low speed tributaries capabilities for new control channels supervision, maintenance & service support to fit any application: audio, video, voice remote and centralized management easy migration from PDH networks fault tolerance • • • • © Trend Communications 5/ 63 SDH is a flexible architecture • • • • • • SDH has a reference model It is an standard universally accepted SDH is highly compatible with SONET very efficient to manage circuits fast circuit definition from a centralized point advanced facilities for quality monitoring © Trend Communications 6/ 63 Circuit provisioning services Internet Frame Relay RTB ATM GSM multiplexing, transport, routing, management, reliability transport network SDH transmission media cable/fiber/radio SDH provides an efficient, reliable and flexible transport for circuits © Trend Communications 7/ 63 SDH architecture client server Section The network is a function of the connectivity Function of inputs outputs connectivity The model considers the network as a connectivity function • • it has a set of input/output interfaces there are function to match requirement with capacities The complexity of the functions moves to use simplified models which allow to define interfaces and overheads © Trend Communications SDH architecture 9/ 63 Topologic partitioning The topology describes the potential connections and are expressed as relations between points on the network • • • the network is an encapsulation that is able to be splitted repeatedly in subnetworks interconnected through links the subnetworks are decomposed until the desired level or when nodes and transmission media are visible (the last layer) nodes are the network elements: switches, multiplexers, and regenerators © Trend Communications SDH architecture 10/ 63 Functional partitioning network connection Client layer digitalization codification Server layer Layer Adaptation: unifies the information format using techniques like mapping, justification, multiplexion, overheads Layer Termination: adds/drops overheads in order to allow a service monitoring and supervision add/drop overheads path The model allow to define independent structures but connected. Each layer can be seen as a network which can be divided in sublayers In PDH the relationships are directs, in SDH are complex and the transport service has been divided in two layers: • • one to connect terminal points (paths) one to connect routes (sections) The model permits also a control of the network elements and a full connection compatibility because all the vendor refer to the same abstract model. © Trend Communications SDH architecture 11/ 63 Reference points Network connection Layer Adaptation Layer Adaptation AP Layer Termination Subnetwork TCP CP • CP link Network connection Layer Termination AP TCP CP CP AP - Access Point: it is the place where are executed the adaptation functions like framing, justification, multiplexing, and alignment. There are two by connection. They are the edge points which can interchange client information CP - Connection Point: it is the place where are implemented the atomic connections. The CP association is known a Subnetwork. A link is the association of two subnetworks. These points are monitored in order to know the network status TCP - Terminal Connection Point: it is the edge CP where it is checked the data integrity. A Network Connection is the association of two TCP SDH architecture 12/ • • © Trend Communications 63 Connectivity Client Path Client layer Server layer AP Network Connection AP Subnetwork Connection TCP CP Link Connection CP Subnetwork Connection TCP CP CP Server Path • • • • A Network Connection is a concatenation of basic elements. The edge points (in/out) are TCP Basis elements are subnetwork connections between CP and links between Subnetworks. The connections can be half-duplex, full-duplex, point to point, point to multipoint, multipoint to multipoint The connection monitors the client information integrity SDH architecture 13/ 63 © Trend Communications Transport stratification 2 Mbit/s circuit 2 Mbit/s level VC12 level DXC Subnetwork connection DXC Subnetwork connection VC12 level path Layer Adaptation Layer Termination VC4 level VC4 level path STM level Layer Adaptation Layer Termination STM-1 section transmission media There is a client/server relationship with headers and adaptation function similar to the OSI layered model used to explain protocols © Trend Communications SDH architecture 14/ 63 Transference integrity: trails client connection Layer Adaptation Layer Adaptation AP trail overheads management overheads management TCP • • • • CP CP CP CP TCP The source delivers information which is adapted: digitalization, codification,... The trail define the transport capabilities and it is able to monitor the integrity and quality of the information interchanged between AP These functions allow to implement the OAM functions (Operation, Administration, and Maintenance) The trails have associated the overhead between the interchange units © Trend Communications SDH architecture 15/ 63 Network Node Interface (NNI) location NNI Tributaries MUX sinc. NNI NNI NNI Tributaries MUX sinc. CXC Media : DIGITAL CONNETION Media : · fiber · wireless ACCESS · fiber · wireless PDH ATM MUX sinc. MUX sinc. MUX sinc. MUX sinc. PDH ATM Tributaries NNI (Network Node Interface) are the connection between subnetworks: • • • NNI are internal network interfaces used to transmit the STM-N frames NNI interface is defined at the access, the transport network; and the interconnection units NNI, PDH, and ATM are SDH network interfaces. They are standards to guarantee the world network interconnections © Trend Communications SDH architecture 16/ 63 Reference model IP IP Frame RTB ISDN Relay ATM ATM Frame Relay ISDN RTB interchange unit paths low order VC-12 high order VC-4 sección de multiplexión multiplexing section VC-12 VC-4 MSOH RSOH STM-1 low order VC-12 high order VC-4 multiplexing section regeneration section physical interface sections sección de regeneración regeneration section physical interface SDH frame optical/electrical/radio NNI © Trend Communications SDH architecture 17/ 63 Network elements and topologies Section Regenerators (REG) STM-N REG STM-N It maintains the physical the signal by means of strength, shape and delay • • • attenuation: reduction of strength of the signal per distance. Amplification delay distortion: the velocity of propagation varies with frequency causing intersymbol interference. Signal needs equalization noise: different causes like thermal noise, intermodulation, crosstalk, impulse noise is always present. The signal must be digitally filtered © Trend Communications SDH architecture 19/ 63 Line Termination Multiplexors (LTMUX) 2M 8M STM-1 L O -P T E 34M 45M 140M H O -P T E SDH MUX STM-N Mux/Demux of plesiochronous circuits to/from STM-N frames • • • The input and the output of the circuit from the SDH network define the paths Are useful for line topologies providing easy migration form legacy PDH networks Overhead management © Trend Communications SDH architecture 20/ 63 Multiplexers (Mux/Demux) STM-N SDH MUX STM-N STM-M M >N Mux/Demux of STM-N signals in/from STM-M • • Does not modify the contents of transported information Multiplexion of four SDH signals: 4 x STM-1 = STM4 4 x STM-4 = STM16 4 x STM-16 = STM64 © Trend Communications SDH architecture 21/ 63 Add & Drop Multiplexer (ADM) West STM-M East STM-M STM-N, PDH Put / get PDH circuits in/from STM-N frames • • configures SDH rings topologies can provide the network with fault tolerant capacities © Trend Communications SDH architecture 22/ 63 Digital Cross-Connect (DXC) STM-N STM-N STM-N STM-N Switchs STM signals as well as add&drop funcionalities. • • • implements all the network element capacities absolutly flexible for subnetwork interconnections allows SDH networks interconnection © Trend Communications SDH architecture 23/ 63 Point to point topology MUX 2M 34M 45M 140M LPT HPT STM-1 SDH MUX REG STM-N MUX MUX STM-N SDH STM-1 MUX 2M HPT LPT 34M 45M 140M MUX • • • Simples but scalable to complex topologies Transport STM signal between two points Allows an smooth migration from legacy PDH networks to SDH © Trend Communications SDH architecture 24/ 63 Ring topology back up ring active ring tributary ADM ADM • • • flexible and scalable provide a native way for reservation circuits allow circuits add&drop at any node © Trend Communications ADM ADM tributary SDH architecture 25/ 63 Star and hub configurations E E D A D A B B C Star PDH network C SDH Network physical topology with star configuration and logical topology with ring configuration • Both configurations allow an smooth migration from PDH infrastructures SDH architecture 26/ 63 © Trend Communications Transport design National Backbone STM-16 Primary Network STM-4 Access Network STM-1 or PDH The networks are designed with topologies that try to drive a lot of traffic through the same ring and a few inter rings or inter layer © Trend Communications SDH architecture 27/ 63 Low Order Paths & High Order Paths LTMUX LO HO MUX REG DXC REG ADM REG LTMUX HO LO HIGH ORDER PATH LOW ORDER PATH The Virtual Container (VC) across the SDH defining a path and two edge points. One where the VC is inserted and the other where it is dropped. There are two types of paths: • • • The High Order Path (HOP) links two points with a high rate transport capacity. The content can be a a circuit of 140 Mbit/s or combination of circuit of 1.5, 2, 6, or 8 Mbit/s The Low Order Path (LOP) links two points with a high rate transport capacity. The content can be a a circuit of 1.5, 2, 6, or 8 Mbit/s The circuits of 34 and 45 Mbit/s can be transported both, into High or Low Order Path © Trend Communications SDH architecture 28/ 63 Multiplexing Section (MS) LTMUX LO HO MUX REG DXC REG ADM REG LTMUX HO LO MULTIPLEXING SECTION MULTIPLEXING SECTION MULTIPLEXING SECTION HIGH ORDER PATH LOW ORDER PATH A section is the space limited by two network elements linked by a transmission media. There are two types: the Multiplexing Section (MS) and the Regeneration Section (RS) The MS is the space defined by two contigous multiplexers. Each MS manages an specifc overhead to control the multiplexers by means of : • • • quality monitoring with alarms/errors detection between Multiplexers provide voice and data channels to configure and operate the Multiplexers facilities for synchonization and automatic protection (APS) SDH architecture 29/ © Trend Communications 63 Regeneration Section (RS) LTMUX LO HO MUX REG DXC REG ADM REG LTMUX HO LO REG SECT REG SECT REG SECT REG SECT REG SECT REG SECT MULTIPLEXING SECTION MULTIPLEXING SECTION MULTIPLEXING SECTION HIGH ORDER PATH LOW ORDER PATH The RS is the space betwen two regenerators united by the any media: fiber, wireless, coaxial. (Pay attention that a Multiplexer works as a Regenerator too.) Each RS manages an specifc overhead to control the Regenerators by means of: • • • quality monitoring with alarms/errors detection between Regenerators provide voice and data channels to configure and operate the Regenerators framing and contents information © Trend Communications SDH architecture 30/ 63 Regeneration process Regeneration Section Regeneration Section Original signal Regenerated signal REG REG ADM attenuation noise distortion Regenerator • • • Multiplexer Regenerator The optical signal must be amplified to compense the attenuation, distortion, and noise during the fiber, cable or wireless propagation. the signal is converted to an electronic signal, then it is filtered and amplified and finally it is converted back to its original nature onother technique to amplifly optical signals is to use Optical Fiber Amplifier (OPA). It consists of a fiber segment (about 70 mtr long) doped with erbiumis and pumped with a light that excites the erbium. And then when a signal passes through the fiber more photons out than photons in: the signal has been amplified SDH architecture 31/ © Trend Communications 63 Transport Services 2 Mbit/s PSTN ADM ADM Internet 2 Mbit/s 34 Mbit/s C irc ui t ADM ADM 34 Mbit/s STM-16 ADM ADM STM-1 LTMUX STM-4 STM-1,4 ADM ADM 140 Mbit/s 155 Mbit/s ISDN ADM ADM LTMUX ATM ATM 2 Mbit/s SDH provides circuit to public switched and routed networks © Trend Communications ADM ADM 2 Mbit/s 34 Mbit/s 140 Mbit/s STM-1 ADM ADM DXC STM-1 ADM ADM GSM SDH architecture 32/ 63 Security A A B B Section Security services When a circuit goes down traffic can not stopped. Reliability is one of the strongest characteristics of SDH networks. In order to assure that has been defined the following strategies: diversification • all the traffic between two sites are divided in several circuits. When one of them goes down the rest of the circuits continue working on restoration • • the routing is a task of the client network (IP, ATM) when a circuit goes down an specialized multiplexer looks for an available circuit and switches the traffic to the alternate path protection • • the routing is a task of the transport network (SDH) alternate circuits have been assigned previously, when a circuit goes down the multiplexer switched the traffic to the back up resource © Trend Communications SDH architecture 34/ 63 Diversification route 1 (50% C1-C2) A C C1 C2 B route 2 (50% C1-C2) D The circuits, between two points, are established using different physical routes. A fault in a transmission route interrupts just a part of the traffic. • • • • It has been used for PDH voice traffic It is an acceptable strategy for no critical circuits In order to provide the same service level it is required to duplicate the number of circuits But most of the times it is no admissible, or possible, to reserve an unused route for each of the network circuits © Trend Communications SDH architecture 35/ 63 Restoration (5,2) A (4,2) (4,5) (7,7) B D B (3,4) (11,3) D C A (6,0) (5,2) (7,0) C (active circuits, protection circuits) (a,p) = There is not a previous assignation of the circuits. • • • • If an active circuit gets down then a protection protocol is executed in order to provide an alternative route The protection circuits share the same network elements and transmission media that are used by the active circuits Pay attention on that: the number of protection circuits is smaller than the active. Using a relation equals to 1/2 for protection circuits could be enough Usually the relation goes from 40% to 80% © Trend Communications SDH architecture 36/ 63 Protection (i) The mechanism is similar to the restoration technic, but there is an previous assignation of circuits before the fault appears SDH path protection • • • • multiplexing section protection for line topologies multiplexing section protection for ring topologies multiplexing section shared protection for line topologies virtual container protection SDH subnetwork protection Is a specialized protection mechanism for all network topologies. It can be used for protecting parts of the network or all the network • • with internal supervision (witch uses information about the own network for switching) with no intrusive supervision (witch uses associated information for switching) © Trend Communications SDH architecture 37/ 63 Linear protection of multiplexing section Same traffic in S and P MUX 1+1 MUX high priority MUX Different traffic in S and P low priority 1:1 MUX service (S) protection (P) MUX 1:N MUX © Trend Communications SDH architecture 38/ 63 Specialized protection: 1 fiber rings Circuit in normal conditions A circuit B circuit protection ring service ring Circuit under protection A circuit in bakup B circuit ADM A circuit B circuit A circuit in bakup B circuit • • • one active ring and one protection ring a new protection ring is established at the multiplexer edge of the fault all the rings are unidirectional © Trend Communications ADM ADM ADM ADM ADM SDH architecture 39/ 63 Ring shared protection with 2 fiber Circuit in normal conditions service circuits service and protection rings Circuit under protection service circuits using protection services two active rings in a single fibre service circuits ADM service circuits using protection services • • • two active rings of one fiber n/2 active circuits and n/2 protection circuits per section to implement uses K1, K2 bytes SDH architecture 40/ © Trend Communications ADM ADM 63 Specialized protection in 2 fiber rings Circuit in normal conditions Circuit under protection circuito A en back up service&protection rings A circuit ADM circuito A circuito A en back up • • • 1 active ring of two fibers 1 protection ring of two fibers Note that rings are bidirectional © Trend Communications ADM ADM ADM ADM ADM SDH architecture 41/ 63 SDH transport services Mbit/s STM-1 AUG VC-n C-n 140, 3 4 ,, 4 5 34 45 + AU (pointer) + HO POH + stuffing bits + justificati on bits + overhead bits M b iit //s Mb t s TUG TU-n VC-n C-n 1.5, 2, 6, 8, 34, 45 + TU ( p o ii n t e r ) (po nter) +LO POH + stuffing bits + justificati on bits + overhead bits Section The SDH multiplexing map 10 Gbit/s STM-64 STM-16 STM-4 STM-1 x1 2,5 Gbit/s 622 Mbit/s AUG16 x4 x1 AUG16 x4 x1 AUG4 x4 x1 AUG x1 x1 x1 AU416c AU44c AU-4 VC416c VC44c VC-4 x3 x1 x1 x1 C416c C-44c C-4 ATM:149760 kbit/s E4: 139264kbit/s 155 Mbit/s x3 x1 AU-3 VC-3 TUG-3 x1 ) SI ( AN TU-3 VC-3 ATM:48384kbit/s T3:44736kbit/s E3: 34368 kbit/s ATM:6874kbit/s T2: 6312kbit/s ATM:2144kbit/s E1:2048kbit/s ATM 1600 kbit/s T1: 1544kbit/s 51 Mbit/s STM-0 (ANSI) x7 (AN SI) x7 x1 TUG-2 x3 x4 TU-12 VC-12 TU-2 VC-2 C-3 C-2 C-12 SI) (AN Frame Pointer processing TU-11 VC-11 C-11 Aliingning Multiplexing POH addition Tributary mapping Container Group © Trend Communications SDH transport services 43/ 63 Transport of PDH circuits, ATM cells and IP datagrams M b i t /s 140, 34, 45 S T M -1 A U G V C -n C -n + AU + HO POH (pointer) + stuffing bits + justificatio n bits + overhead bits TUG T U -n V C -n C -n Mbit/s 1.5, 2, 6, 8, 34, 45 + TU (pointer) +L O P O H + stuffing bits + justificatio n bits + overhead bits The mapping in standarized structures to provide circuits • • • PDH, and T-Carrier hierarchies are mapped in specific Containers (C-n) ATM cells are mapped also in Containers C-n IP datagrams are mapped in Containers C-n © Trend Communications SDH transport services 44/ 63 Containers autonomous master clock PDH frames mapping stuffing justification bit oriented synchronized master clock synchronism SDH container 2Mbit/s MUX 8Mbit/s 2Mbit/s mapping stuffing justification byte oriented MUX 155Mbit/s The mapping operation: • • • • Multiplexers adjusts the capacity of containers with the provided info using byte stuffing The containers have justification mechanism byte oriented also The multiplexing function is a synchronous operation because all the network multiplexers must use the same clock. With PDH it is not mandatory to synchronize the network equipments SDH transport services 45/ 63 © Trend Communications The container C-4 C-4 11 1 270 Byte sequence in every row of a C-4 (260 bytes) 1 12 1 12 1 12 1 12 1 12 I 1 C-4 row I X X X I I I I I S S S S S I I I I I S S S S Z I I I I I S S S S I I I I column 11 X X 9 column 270 I X Z S : information byte(s) from a 139264 Kbit/ s i g n a l s = CSSSSSOO = I I I I I IJ S : stuffing byte I: Information bit S: Stuffing bit C: Justification control bit J: Justification opportunity bit O: Overhead bit During the mapping operation the multiplexer receives the tributary which is placed into the container, justification bytes are used to accomodate the clock differencies, and the stuffing to fill the extra space up. • • • The C-4 container provides big capacity services It provides transport for E4 circuits (139264 kbit/s) ATM cell can be mapped directly in C-4 SDH transport services 46/ © Trend Communications 63 The VC-4 Virtual Container C -4 into a V C -4 10 1 11 270 J1 B3 C2 G1 F2 H4 F3 VC-4 Path Overhead (POH) is added 9 K3 N1 • • • C4+POH=VC4 The Path Overhead (POH) is added and will travel together until the termination point Only the termination multiplexer is allowed to modify the POH contents © Trend Communications SDH transport services 47/ 63 AU pointer association 1 9 10 STM-1 10 11 270 RSOH VC-4 270 AUG J1 B3 C2 G1 MSOH F2 H4 F3 K3 N1 POH The ALIGNING process associates a pointer • • The pointer allows to find the VC-4 The pointer occupies always a fixed position inside the STM-1 frame. The VC-4 does not occupies a fixed position in the frame to adapt clock impairments © Trend Communications SDH transport services 48/ 63 VC4 insertion to the STM-1 frame V=150 km/h VC-4 155 km/h STM-1 STM-1 STM-1 VC-4 VC-4 VC-4 Containers exactly allocated perfect synchronization © Trend Communications SDH transport services 49/ 63 VC4 insertion to the STM-1 frame (ii) V