updated 1/2002 1

SONET / SDH

Nirmala Shenoy

Information Technology Department

Rochester Institute Technology

updated 1/2002 2

SONET / SDH

• Scope– What is SONET/SDH – features– Signal hierarchy– Topologies– SONET components– Layers– Frames– Virtual tributaries

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SONET / SDH

• What is SONET / SDH?– Synchronous Optical Network – ANSI (US)– Synchronous Digital Hierarchy –ITU-T Europe– Similar and compatible– A standard to be used for fibre optics– Recommendation for FOTS equipment

• Fibre Optic Transmission Systems

– Can carry incompatible DS-0, DS1 (Asyn)

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SONET / SDH

• What is SONET / SDH?– Single reference clock

• synchronize transmissions

– Predictability– Powerful frame – Transmission envelope

• Multiplex channels

– Multiplexed transport mechanism • Optical based Carrier System

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SONET / SDH

• What is SONET / SDH?– Self healing ring topology– Consolidate and segregate traffic from different

end-points– Extensive integrated OAM&P– Backward compatibility

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SONET / SDH

• Signal Hierarchy– STS – Synchronous Transport Signals

• support a certain base data rate- 51.84Mbps

• STS 1 – STS 192 – different hierarchies

– Corresponding carrier System • Optical Carrier – OC-1, OC-3, OC-12, OC-48

– SDH – STM – Synchronous Transport Module• STM 1 = STS 3

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SONET / SDH• Sonet/SDH ratesSTS 1 OC-1 51.840STS-3 OC-3 155.520 STM-1STS-9 OC-9 466.560 STM-3STS-12 OC-12 622.080 STM-4STS-18 OC-18 933.120 STM-6STS-24 OC-24 1244.160 STM-8STS-36 OC-36 1866.230 STM-12STS-48 OC-48 2488.320 STM-16STS-96 OC-96 4976.640 STM-32STS-192 OC-192 9953.280 STM-64

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SONET / SDH

• Configuration

STS MUX STS MUX

regenerator regenerator

Add/drop mux

section section

line

path

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SONET / SDH

• SONET topology

ADM

ADM

DCS

ADM

ADM

ADM

SMD

SMD

SMD SMD

SMD SA

SA

DS1

802.5

ADM – add drop multiplexer SMD- sts mu/demux DCS – digital cross connect switch SA – service adapter

Oc-n

Oc-n

Oc-n

Oc-n

Oc-n

Oc-n

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SONET / SDH

• Multiplexing

MUX/DMUX

Service Adapters

Service Adapters

Service Adapters

DS1, CEPT1 etc

Maps into virtual tributaries

DS3 STS-1

STS-n

MAN, ATM, SMDS, others

STS-n

E/O

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SONET / SDH

• SONET Devices

• STS Multiplexer– Multiplexes and de-multiplexes signals from

multiple sources– Path terminating equipment– Maps user payload into standard frame– Header goes end-to-end as part of Synchronous

Payload Envelope - SPE

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SONET / SDH

• SONET Devices

• Add /Drop Multiplexer– Adds signals from different sources/removes– Uses header address information to identify

stream and remove– Line terminating Equipment– Performs multiplexing, synchronization, APS

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SONET / SDH

• SONET Devices

• Regenerator– Repeater – improves signal quality– Operations – include layer 2

• Frame alignment, scrambling, error monitoring

– Section terminating equipment

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SONET / SDH

• Section– Connects two neighboring devices

• Line– Connects two multiplexers (STS , Add/Drop)

• Path– Connects two STS Mux/demux

• Layers – likewise – path, line, section

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SONET / SDH

• SONET layers

PATH layer

LINE layer

SECTION layer

photonic layer

Data link

Physical

updated 1/2002 16

SONET / SDH

• Photonic layers – phy – Specs for optical fiber channel– NRZ encoding used

• Power level

• Wavelength

• Pulse shape

updated 1/2002 17

SONET / SDH

• Section layer– Frames – identifies beginning of frame– Scrambling – introducing 1’s to derive clock– error monitoring – section level– Adds 9 bytes to header – frame size 810 bytes– Provided at all devices

updated 1/2002 18

SONET / SDH

• Line layer– Locates partial payload – virtual tributaries– Provides frequency justification, bit stuffing

• To adjust to clocking from different systems

– Does APS – Adds 18 bytes to header– Provided at the STS Mux and Add/Drop Mux

updated 1/2002 19

SONET / SDH

• Path layer– Converts to optical signals and back to

electromagnetic– Adds 9 bytes to header - is part of SPE– Defines the payload being carried– End-to-end path control– Support virtual tributaries– Provided at the STS Mux

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SONET / SDH

• SONET STS-1Frame

Frame1

Frame2

Frame8000

Frame = 810 octets * 8 = 6480bits 8000 frames/sec = 6480*8000 bits/sec = 51.84Mbps

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SONET / SDH

• SONET Frame– Matrix of nine rows – 90 octets each– First 3 columns (octets) – three rows

• section overhead – 9 bytes

– Next 6 rows – line overheads – 18 bytes– Rest of the frame – Synchronous Payload

Envelope – SPE – 9 bytes of path overheads

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SONET / SDH

– first column in SPE – path overhead

STS SPE

Path overhead

Section overhead

line overhead

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SONET / SDH

• Section overhead– Alignment bytes (A1 & A2)– framing and

synchronization – pattern F628hex– Identification byte (C1)–unique id for the STS-

1 frame– Parity byte (B1)– Order-wire byte (E1)– bytes in consecutive

frames – form a communication channel between regenerators

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SONET / SDH

• Section overhead– User’s byte (F1)– bytes in consecutive frames

form a channel for user needs at the section level

– Management bytes (D1, D2 and D3)- 3 bytes per frame in consecutive frames = 192 kbps for OAM

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SONET / SDH

• Line Overhead– Pointer bytes (H1, H2, H3)– 3 bytes – identify

location of the payload – Line Parity byte (B2)– Automatic Protection Switching bytes 2 bytes

(K1, K2) – consecutive frames- 128 kbps channel to detect problems in multiplexers

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SONET / SDH

• Line Overhead– Data communication channel bytes (D4-D12) –

consecutive frames – 576 kbps OAM at the line– Growth bytes (Z1, Z2) – future use– Orderwire byte (E2) – line level

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SONET / SDH

• Path Overhead– Path trace byte (J1) – bytes in consecutive

frames – path tracking – verify connection– Path parity byte (B3) – Path signal label byte (C2) – path id – gives the

construction details of the SPE– Path Status byte (G1) –receiver communicates

its status

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SONET / SDH

• Path Overhead– Path user channel byte (F2) user needs at path

level– Virtual tributary indicator (H4) –multi-frame

indicator – payload not fitting into a frame– Growth byte (Z3, Z4, Z5) – reserved–

updated 1/2002 29

SONET / SDH

• Virtual Tributaries– Partial payload share a frame– The SPE has a number of tributaries– VT1.5 = 8000 frames * 3 columns * 9 rows * 8

bits = 1.728 Mbps DS-1 service– VT2 = 8000 frames*4 columns*9 rows * 8 bits

= 2.304 Mbps CEPT-1

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SONET / SDH

• Virtual Tributaries– VT3 = 8000 frames * 6 columns * 9 rows * 8

bits = 3.456 Mbps DS-1C– VT6 = 8000 frames*12 columns*9 rows * 8

bits = 6.912 Mbps DS-2

updated 1/2002 31

SONET / SDH

• Summary– A carrier system – optical carriers– Synchronous transmission - faster– Time Division multiplexing– High speed backbone– Support for high bit rate applications?– Add/Drop multiplexers– Self healing rings