Transcription

Fundamentals ofSONET/SDHP. Michael [email protected] Michael Henderson, [email protected] Copyright 20021

AgendaWhy SONET/SDH?Historical backgroundBasic structure of the SONET/SDH frameTransport overheadPayload pointer processingPayload overheadMapping of SONET payloads Virtual tributaries Handling ATM, POS, and GFP Automatic protection switching Summary This presentation is based on a white paper available at http://www.michaelhenderson.us/Papers.htm titled “Fundamentals of SONET/SDH.”2014-04-09PMHP. Michael Henderson, [email protected] Copyright 20022

What is SONET/SDH SONET – Synchronous Optical NETwork (ANSI). ANSI started work on SONET in1985. SDH – Synchronous Digital Hierarchy (ITU). The ITU began work in 1986 to achieve the same goal. SONET and SDH define a set of physical layer standards forcommunications over optical fiber.I will attempt to cover both SONET and SDH in this presentation.However, SONET and SDH use different terminology, which makesit difficult to talk about both at the same time.I will talk mainly about SONET because you need to understandSONET to understand why some things were done in SDH.2014-04-09PMHP. Michael Henderson, [email protected] Copyright 20023

Why SONET/SDH? Originally, all communications in the telephone network wasanalog. Analog lines or analog microwave was used to connect toswitching offices.Many individual analog linesSwitching office2014-04-09PMHSwitching officeP. Michael Henderson, [email protected] Copyright 20024

Why SONET/SDH? In about 1962, the network providers began using digitalcommunications between switching centers. In the US, this was the D1 channel banks and T-carriersystems.Analog linesAnalog linesChannelbankSwitching office2014-04-09PMHTwo pairs of copperwires (Tx and Rx)ChannelbankSwitching officeP. Michael Henderson, [email protected] Copyright 20025

Why SONET/SDH? As communications needs grew, many T- or E-carrier lineswere needed between switching centers. In the late 1970’s optical communications began to be usedto interconnect switching offices.T1 linesT1 linesTerminatingmultiplexerSwitching office2014-04-09PMHTwo optical fibers(Tx and Rx)TerminatingmultiplexerSwitching officeP. Michael Henderson, [email protected] Copyright 20026

Standardization of SONET/SDH Prior to standardization, every manufacturer of opticalcommunications used their own framing. Did not allow multi-vendor networks. The ANSI T1X1.5 committee began work in 1985 to definestandards for optical communications which would allow “amid-span meet”. The ITU began work in 1986 to achieve the same goal. Both bodies finalized their first set of standards in 1988.2014-04-09PMHP. Michael Henderson, [email protected] Copyright 20027

Why do we need SONET/SDH All data requires framing. Since optical networks are complex, provisions are made formanagement information. Many other things are provided. Multiplexing. Error checking. Handling variations in clocks. Mapping of plesiochronous voice and data traffic. Signaling for automatic switching in case of a fiber or nodefailure.2014-04-09PMHP. Michael Henderson, [email protected] Copyright 20028

SONET/SDH nTerminationADMPathTerminationPTE Path Terminating EquipmentLTE Line terminating EquipmentSTE Section Terminating EquipmentADM Add/Drop Multiplexer2014-04-09PMHP. Michael Henderson, [email protected] Copyright 20029

STS-1 SONET FrameA1/A2 0xf62812Order oftransmission9 H4D7D8D9Z3D10 D11 D12Z4S1 M0/1 E2N13 Columns oftransport OH2014-04-09PMHOne column ofpayload OH90 ColumnsSynchronous PayloadEnvelope (SPE) – 87 columnsSection overheadPayload overheadLine overheadDataP. Michael Henderson, [email protected] Copyright 200210

STS-1 Frame Format 9 rows by 90 columns – 810 octets in the frame. Frame is transmitted from left to right, by row. Frames are transmitted 8,000 times per second, every 125 seconds. STS-1 bit rate is therefore 51.84 Mbps (810 octets x 8,000times per second x 8 bits per octet). This lowest level SONET signal is called a SynchronousTransport Signal, level 1 (STS-1). Once the scrambler isapplied, it is known as an Optical Channel, level 1 (OC-1). The lowest level SDH signal is know as a SynchronousTransport Module, level 1 (STM-1).2014-04-09PMHP. Michael Henderson, [email protected] Copyright 200211

SONET/SDH data rates2014-04-09PMHSONET nameSDH nameLine rate (Mbps)SPE rate (Mbps)OC-1STM-051.8450.112Overhead -25639,813.1238,486.0161,327.104P. Michael Henderson, [email protected] Copyright 200212

Interleaving of SONET/SDH signalsOrder oftransmission132014-04-09PMHA1 A2 J02A1 A2 J0 J1B1 E1 F1A1 A2 J0 J1B1 E1 F1 B3D1 D2 D3B1 E1 F1 B3D1 D2 D3 C2H1 H2 H3D1 D2 D3 C2H1 H2 H3 G1B2 K1 K2H1 H2 H3 G1B2 K1 K2 F2D4 D5 D6B2 K1 K2 F2D4 D5 D6 H4D7 D8 D9D4 D5 D6 H4D7 D8 D9 Z3D10 D11 D12D7 D8 D9 Z3D10 D11 D12 Z4Z1 Z2 E2D10 D11 D12 Z4Z1 Z2 E2 Z5S1 M0/1 E2 N1J1B3C2G1F2H4Z3Z4Z5P. Michael Henderson, [email protected] Copyright 200213

Interleaving of SONET/SDH signals270 XD9XXD10XXD11XXD12XXS1Z1Z1 M0/1 Z2M2E2XXFirst STS-12014-04-09PMHSecond STS-1Third STS-1P. Michael Henderson, [email protected] Copyright 200214

Payloads in Interleaved SignalsA1 A2 J0A1 B1A2 E1J0 F1A1 B1A2 E1J0 F1D2 D3B1 D1E1D1F1D2 H2D3 H3H1D1 H1D2 H2D3 H3B2 K1 K2H1 B2H2 K1H3 K2D4 D5 D6B2 D4K1 D5K2 D6D8 D9D4 D7D5D7D6D8 D11D9 D12D10D7D10D8D11D9D12Z1 Z2E2D10 Z1D11 Z2D12E2S1 M0/1 E22014-04-09PMH87 3Z4Z5Z4Z5N1P. Michael Henderson, [email protected] 200215

Concatenated Payloads261 ColumnsJ1B3C2G1F2H4Z3Z4N1(N/3) – 1 Columns of fixed stuff2014-04-09PMHP. Michael Henderson, [email protected] Copyright 200216

Concatenated PayloadsA1 A2 J0A1 B1A2 E1J0 F1A1 B1A2 E1J0 F1D2 D3B1 D1E1D1F1D2 H2D3 H3H1D1 H1D2 H2D3 H3B2 K1 K2H1 B2H2 K1H3 K2D4 D5 D6B2 D4K1 D5K2 D6D8 D9D4 D7D5D7D6D8 D11D9 D12D10D7D10D8D11D9D12Z1 Z2E2D10 Z1D11 Z2D12E2S1 M0/1 E2261 ColumnsJ1B3C2G1F2H4Z3Z4N12014-04-09PMHP. Michael Henderson, [email protected] Copyright 200217

Framing and Section D5D6D7D8D9D10D11D12S1M0/1E2 Two octets used for framing: A1, A2. Bit pattern is A1 1111 0110, A2 0010 1000 Higher levels of STS-N have N A1 octets and NA2 octets. Section Trace (J0) is used to verify continuedconnection between section entities.P. Michael Henderson, [email protected] Copyright 200218

Monitoring for Bit 4D5D6D7D8D9D10D11D12S1M0/1E2 Does a bit interleaved parity (BIP-8) over theoctets in the (previous) frame. Even parity. Parity check applies to previous frame Separate check for section and line. Only one B1 octet, no matter what the STS-N. One B2 octet for each STS-N.P. Michael Henderson, [email protected] Copyright 200219

Communication 2D4D5D6D7D8D9D10D11D12S1M0/1E2 E1, E2 (orderwire) was intended to be used bycraftspersons while installing a line.Craftspeople use cellular phones so this octetis not used very much. F1 is available for the network provider to useas they wish.P. Michael Henderson, [email protected] Copyright 200220

Communication 2D4D5D6D7D8D9D10D11D12S1M0/1E2 These channels are used for networkmanagement. Technically, D1, D2, D3 is intended for sectionmessages but this is not always adhered to.P. Michael Henderson, [email protected] Copyright 200221

Automatic Protection K2D4D5D6D7D8D9D10D11D12S1M0/1E2 These octets (K1, K2) are used to sendmessages between two nodes when a failureis detected between them. Messages are sent both ways around the ring(if possible). Last four bits of K1 specifies the address ofthe addressed node. First four bits of K2 specifies the address ofthe sending node. Means that there can only be 16 nodes on aring.P. Michael Henderson, [email protected] Copyright 200222

Sync and Error 1K2D4D5D6D7D8D9D10D11D12S1M0/1E2 S1 is used for synchronization status. M0/M1 is used to send back to the sender, theerror status of the received signal (determinedby the Bx octets).P. Michael Henderson, [email protected] Copyright 200223

Payload 2D4D5D6D7D8D9D10D11D12S1M0/1E2 The H1, H2 octets are joined to form a pointerwhich points to the first octet of the SPE. The first 4 bits of the 16 bits indicates if thepointer is changing. The next two bits are not used. The last 10 bits are the pointer and can have avalue from zero to 782. H3 is used to carry a payload octet when anegative pointer adjustment is done. These octets are covered in additional detail inthe next slides.P. Michael Henderson, [email protected] Copyright 200224

Why do we need Payload Pointers?Network box which takes trafficfrom one side and passes italong to the other side1,000,000 bits/secFIFO1,000,001 bits/secEvery eight seconds, the FIFO will run dry. If an extra, “meaningless”octet can be sent at that time, it will give the FIFO time to fill up again.Problem: How to tell the receiver that this one octet is meaningless?2014-04-09PMHP. Michael Henderson, [email protected] Copyright 200225

Format of the H1, H2, H3 OctetsH2H2H1H11 2H3H33 4 5 678 9 10 11 12 13 14 15 16N N N N – –ID0 1 1 00 0I D IDID10 BIT POINTERNNNN New data flag (NDF)I Increment bitsD Decrement bits2014-04-09PMHD INEGATIVE STUFFOPPORTUNITYP. Michael Henderson, [email protected] Copyright 2002POSITIVESTUFFOPPORTUNITY26

A Negative Pointer AdjustmentNormal FrameNormal FrameH1 H2 H3H1 H2 H3“D” bits inverted.H1 H2 H3Pointer updated.H1 H2 H32014-04-09PMHThis line has no meaning –it’s just there to help showthe movement of the start ofthe frame (here).Note that H3 is being used tocarry a payload octetThe pointer is invalidhere because of the“D” bit inversion. Thevalue without inversionis the same as the previousframe.P. Michael Henderson, [email protected] Copyright 200227

Details of H1, H2, H3 octets during justificationNegative Justification using Inverted “D” BitsFrame statusNew Data FlagUnusedIDIDIDIDIDNormal frame0110XX0001111110Invert “D” Bits0110XX0100101011New ptr value0110XX0001111101New ptr value0110XX0001111101Normal frame0110XX00011111012014-04-09PMHP. Michael Henderson, [email protected] Copyright 200228

A Positive Pointer AdjustmentNormal FrameNormal FrameH1 H2 H3H1 H2 H3“I” bits inverted.H1 H2 H3Pointer updated.H1 H2 H32014-04-09PMHThis line has no meaning –it’s just there to help showthe movement of the start ofthe frame (here).Positive stuffoctetThe pointer is invalidhere because of the“I” bit inversion. Thevalue without inversionis the same as the previousframe.P. Michael Henderson, [email protected] Copyright 200229

Details of H1, H2, H3 octets during justificationPositive Justification using Inverted “I” BitsFrame statusNew Data FlagUnusedIDIDIDIDIDNormal frame0110XX0001111110Invert “I” Bits0110XX1011010100New ptr value0110XX0001111111New ptr value0110XX0001111111Normal frame0110XX00011111112014-04-09PMHP. Michael Henderson, [email protected] Copyright 200230

Details of H1, H2, H3 octets when using NDFOne Octet Negative Adjustment using the NDFFrame statusNew Data FlagUnusedIDIDIDIDIDNormal frame0110XX0001111110NDF indicator1001XX0001111101New ptr value0110XX0001111101New ptr value0110XX0001111101Normal frame0110XX00011111012014-04-09PMHP. Michael Henderson, [email protected] Copyright 200231

Details of H1, H2, H3 octets when using NDFOne Octet Positive Adjustment using the NDFFrame statusNew Data FlagUnusedIDIDIDIDIDNormal frame0110XX0001111110NDF indicator1001XX0001111111New ptr value0110XX0001111111New ptr value0110XX0001111111Normal frame0110XX00011111112014-04-09PMHP. Michael Henderson, [email protected] Copyright 200232

Payload OverheadJ1B3C2G1 Path trace (J1) used to check continuedconnection between the path devices (end-toend). 64 octet for SONET and 16 octet for SDHmessage.F2H4Z3Z4N12014-04-09PMHP. Michael Henderson, [email protected] Copyright 200233

Error CheckingJ1B3C2 BIP-8 parity check over the payload, only. Even parity. Parity is for previous payload, not this one.G1F2H4Z3Z4N12014-04-09PMHP. Michael Henderson, [email protected]el-henderson.us Copyright 200234

Path Signal LabelJ1B3C2G1F2 Indicates the type of payload carried in the SPE. For our discussion, we’ll be interested in avalue of 0x02 for floating virtual tributary (VT)mode, 0x04 for asynchronous mapping of DS-3,0x13 for mapping of ATM, 0x16 for packet overSONET (POS), and 0x1b for generic framingprocedure (GFP).H4Z3Z4N12014-04-09PMHP. Michael Henderson, [email protected] Copyright 200235

Path Status and Path User ChannelJ1B3C2G1F2 The G1 octet (Path Status) sends informationback to the sender indicating the number ofparity errors, or if a complete failure isdetected. The F2 octet is a user channel for Pathapplications (end-to-end). It is not subject tostandardization (anything can be put into it).H4Z3Z4N12014-04-09PMHP. Michael Henderson, [email protected] Copyright 200236

Multi-Frame IndicatorJ1B3C2G1F2 The last two bits of this octet counts from 00to 11 continuously to provide a multi-frameindicator for VT payloads (to be explainedlater). Some of the other bits are being defined foruse with virtual concatenation but will not bedescribed here.H4Z3Z4N12014-04-09PMHP. Michael Henderson, [email protected] Copyright 200237

TCM and Reserved octetsJ1B3C2G1 The Z3, Z4 octets are reserved for futurestandardization and have no meaning today. The N1 octet is for tandem connectionmonitoring and is fairly complex. No attemptwill be made here to explain it.F2H4Z3Z4N12014-04-09PMHP. Michael Henderson, [email protected] Copyright 200238

Virtual Tributaries2014-04-09PMHP. Michael Henderson, [email protected] Copyright 200239

Plesiochronous Data Rates of Interest2014-04-09PMHType of DigitalCircuitBit Rate(Mbps)DS-1 (T1)1.544E12.048DS-1C3.152DS-26.312DS-3 (T3)44.736P. Michael Henderson, [email protected] Copyright 200240

STS-1 Payload MappingPayloadoverhead(POH)87 Columns28 Cols28 Cols28 ColsJ1B3C2G1F2H4Z3Z4N113059All mappings of payload into an STS-1 payload have these two columnstaken as stuff columns.2014-04-09PMHP. Michael Henderson, [email protected] Copyright 200241

Virtual Tributary GroupsVxVxVxVxVxVxVxThe “x” in Vx goesfrom 1 to 4Order oftransmission123When interleaving,the first columnof VTG#1 goesnext to the POH.Columns 30 & 59of the SPE areskipped.2345671The 84 usable payload columns are divided into seven groups of twelvecolumns. Each set of twelve is called a “Virtual Tributary Group” (VTG)2014-04-09PMHP. Michael Henderson, [email protected] Copyright 200242

Virtual Tributaries A Virtual Tributary Group is further subdivided into VirtualTributaries (VT). Three columns makes a VT-1.5 (1.728 Mbps gross, good for aDS-1 at 1.544 Mbps). Four columns makes a VT-2 (2.304 Mbps gross, good for an E1at 2.048 Mbps). Six columns makes a VT-3 (3.456 Mbps gross, good for a DS1C at 3.152 Mbps). Twelve columns makes a VT-6 (6.912 Mbps gross, good for aDS-2 at 6.312 Mbps). A VTG contains four VT-1.5s, or three VT-2s, or two VT-3s, orone VT-6. A VTG can only contain one kind of VT. Different VTGs in anSPE can contain different VT types, but within a VTG, therecan only be one kind of VT.2014-04-09PMHP. Michael Henderson, [email protected] Copyright 200243

Virtual Tributaries – The VT-1.5One VTGVxOne VT-1.5 Vx Vx VxIf all the VTGs inan STS-1 arecarrying VT-1.5s,the capacity ofthe STS-1 SPE is28 DS-1s, or thesame as a DS-3.(Seven VTGstimes four VT-1.5sper VTG)The four VT-1.5s are interleaved into the VTG. Note the colors – there arethree of each color, with each color indicating one VT-1.5 (for four inside theVTG. Each VT is 27 octets, with one octet taken for the Vx octet.2014-04-09PMHP. Michael Henderson, [email protected] Copyright 200244

Superframes Remember that the last two bits of H4 in the POH count 00,01, 10, 11, 00, etc. This produces a superframe of fourframes. The frame after the SPE with an H4 value of 00 will have thefirst octet in the VT identified as V1. The one after value 01will be identified as V2, etc. V1 and V2 form a pointer, exactly like the H1, H2 octets. Bits 5 and 6 are used to indicate the type of VT (unused in H1,H2) (VT-6 00, VT-3 01, VT-2 10, VT-1.5 11) V3 is the negative stuff opportunity, exactly like H3. V4 is reserved for future standardization.V12014-04-09PMHV2 V3V4P. Michael Henderson, [email protected] Copyright 200245

The V1, V2 T2VT1.5NEW DATA FLAG – INVERT 4 N BITSNEGATIVE STUFF – INVERT 5 D BITSPOSITIVE STUFF – INVERT 5 I BITS2014-04-09PMHDIDIDIDID10 BIT POINTER10 BIT POINTER10 BIT POINTER10 BIT POINTERI – Increment BitD – Decrement BitN – New Data Flag BItS - VT Size BitP. Michael Henderson, [email protected] Copyright 200246

Pointing to the Start of the VT PayloadPointer value of zeroV1V4V3V2Pointer value of 103V1V2V3A VT-1.5 is made up of three columns of 9 octets or27 octets. Four frames make a supreframe, or 108octets. Once the V1, V2, V3, V4 octets are removedfrom the count, we have 104 octets remaining.Since the pointer counts from zero, the highestvalue of the pointer is 103.2014-04-09PMHP. Michael Henderson, [email protected] Copyright 200247

The VT-1.5 PayloadV5J2Z6Z7Frame 3Frame 426 octetsFrame 12014-04-09PMHFrame 2P. Michael Henderson, [email protected] Copyright 200248

Byte Synchronous and Asynchronous VTs We’re going to look at two ways that DS-1 traffic can becarried in a VT payload – byte synchronous andasynchronous. Byte synchronous preserves the location of the payloadoctets in a T1 frame (each speech sample). Used primarily to transport channelized T1s which are carryingvoice calls. Asynchronous simply transports the 1.544 Mbps streamwithout concern for which byte is which. Used to carry T1s which are carrying data. Bits 5, 6, & 7 of V5 indicate which is being carried (010 asynchronous, 100 byte synchronous).2014-04-09PMHP. Michael Henderson, [email protected] Copyright 200249

Byte Synchronous Mapping – VT-1.526 S3S4FRP1P0S1S2S3S4FR24 DS-0Channels24 DS-0Channels24 DS-0Channels24 DS-0ChannelsFrame 1Frame 2Frame 3Frame 4R Fixed stuff bitF DS-1 framing bitSx Signaling bits, A, B, C, D bits in a DS-1Px Phase bits, indicates which frame set for SF or ESF framing2014-04-09PMHP. Michael Henderson, [email protected] Copyright 200250

Asynchronous Mapping – VT-1.5V5RRRRRRIR26 octetsJ2Z6Z7C1C2O O O O I RC1C2O O O O I RC1C2R R R S1S2R24 Octets(192 bits)24 Octets(192 bits)24 Octets(192 bits)24 Octets192 bits)Frame 1Frame 2Frame 3Frame 4R Stuff bits – no meaningO Future standardization – unusedI Information bit. Makes the 193rd bit ofa DS-1 frame2014-04-09PMHCx Controls use of the S bits.Sx Stuff bits. May or may not carryinformation bits, dep