optical transport network (otn)

7/27/2019 Optical Transport Network (OTN)

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Optical Transport Network (OTN)

ITU-T standard G.709

”G.709 – The Optical TransportNetwork (OTN)”



Why OTN?

• Standard for optical networks required – Optical interconnection between equipment from different

vendors – Optical interconnection between different operators

• Once called “digital wrapper” because it wraps any client signal in

overhead information for operations,administration, andmanagement• Framing of client signal of different protocols for transport over the

physical optical layer – E.g. IP/Ethernet or IP/ATM or SDH

• Takes SDH/SONET further, enabling optical functionality – From a single to multiple wavelengths – Forward Error Correction (FEC) – What is FEC?



Properties of OTN

• Protocol transparency – Handles “any” protocol-stack and gives a physical layer to higher layer

protocols like e.g. IP

•Backward compatibility for existing protocols – Handles both SDH and Ethernet

• FEC – Reduces cost, improves performance

• Reduction of 3R regeneration – Allows management of all-optical network elements



Interfaces

• Inter-domain interfaces (IrDI) – Location between networks of two operators

– Location between sub-networks of two vendors in the same operator

domain

– The location within the sub-network of one vendor

– 3R regeneration – Why?

• Intra-Domain interfaces (IaDI) –

The location between the equipment of an individual manufacturer’ssub-network

– Transparent network



Inter and intra -domain• Intra- IaDI within e.g. an operator

•Inter- IrDI between operators or connection toe.g. a customer (client)



OTN ayer structure• OCh = Optical channel

•

OMS = Optical Multiplex section• OTS = Optical Transmission Section



OTN hierarchy

Client

OH Client

OH OPUk

OH ODUk FEC

OCh payload

Client

OPU

ODU

OTU

OMS payload

OTS payload

OCCp OCCp OCCp OCCp OCCp OCC

N o n

A s s o c i a t e

d

o v e r h e a d



In-band and out of band OH

• Non-associated OH (out of band) may be

added to OCh enabling management of

multiple colours in OTN.

• Optical Multiplex Section (OMS) – Multiplex of OCh’s

• Optical Transmission Section (OTS) – The transmission medium, I.e. the fibre



OTN (G.709) frame

ClientODU-OH

O P U - O H

OTU-OHFAS

FEC

1 7 8 14 15 1617 3824 3825 4080

RES

PT

PSI

RES TCM/ACT FTFLTCM6 TCM5 TCM4TCM3 TCM2 TCM1 PM EXP

RESAPS/PCCGCC2GCC1



• ACT: Activation/deactivation control channel

• APS: Automatic Protection Switching

• PCC Protection Communication Channel

• EXP: Experimental, 2 bytes

• FAS: Frame Alignment Signal, 6 bytes, are used to delineate the frame

• FTFL: Fault Type & Fault Location, 256 byte, faults in the forward and

reverse directions

• GCC: General Communication Channel, 2 bytes

• MFAS: MultiFrame Alignment Signal

• PCC: Protection Communication Control channel

• PM: Path Monitoring, 3bytes monitor the end-to-end path



• PSI: Payload Structure Identifier , 256bytes

• RES: Reserved for future international

• SM: Section Monitoring, trail trace identifier,BIP-8 byte, and alarm signals

• TTI: identification of the two end points of the optical connection

• BIP-8: (bit interleaved parity8) used to monitor the bit error rate

• alarm signals : backward error indicator

• TCM: Tandem Connection Monitoring , to monitor the error performance of

a signal for different applications



Optical Payload Unit (OPU)

• Framing of client signal – May be of any protocol, e.g. SONET/SDH, GFP, IP, GbE

• Payload Structure Identifier (PSI) – 256 Byte message

– Justification bits for asynchronous mapping of client signal

– PSI0 contains Payload Type (PT) (single byte) identifying type of

payload

– RES – Bytes Reserved for future use



Optical channel Data Unit (ODU)

functionality

• Tandem Monitoring (TCM)

– Hierarchical error checking using parity bytes

– Allows up to six tandem connections, nesting and overlapping

• Path Monitoring (PM)

– Monitoring of particular sections

– Fault location

• General Communication Channels (GCC)

– Typically Management communication

• Automatic Protection Switching (APS)

– Protection switching at one or more levels

– What is protection switching?



ODU-k: Defined for several bitrates

• -k is a number defining the bitrate

• Originally defined bitrates – ODU1: 2.5 Gb/s

– ODU2: 10 Gb/s

– ODU3: 40 Gb/s

• Recently defined/to be defined – ODU0: 1 Gb/s (Matches Gigabit Ethernet)

– ODU4: 100 Gb/s (Matches 100 Gigabit Ethernet)

T d C ti it i



Tandem Connection monitoring• Six levels, nested or cascaded connections

• Nested: A1-A2/B1-B2/C1-C2 and A1-A2/B3-B4Cascaded: B1-B2/B3-B4

• Carriers may maintain their own service levelagreement (SLA) –

What is a SLA?

Figure from

G.709

standard



Optical channel transport unit (OTU)

• Support transport of OTU via one or more

optical channel connections

• Frame alignment Signal (FAS) – Multi Frame Alignment Signal (MFAS)

– ODU frames may span multiple OTU frames

– TTI and TCM-ACT (activation) signals requires multiple ODU-frames for

being processed

• Forward Error Correction (FEC)



Forward error control(FEC)16 FEC blocks of 16 bytes for the row. 64 bytes/frame

Reed-Solomon RS(255,239) code

Uses 16 byte interleaved codecs.

Can correct up to eight symbol errors(correctionmood) and detect up to 16 symbol errors in the code

(detection mood).

Enables communications to maintain acceptable

performance quality in noisy environment.Provide additional coded data for error checking and

error correction



Physical impairments to be

compensated

• Linear

– Attenuation

– Noise

– Dispersion: Chromatic, mode and polarisation

• Non-linear

– Four wave mixing

–

Self phase modulation – Cross phase modulation



Multiplexing

• Wavelength Division Multiplex (WDM)

• Time Division Multiplex (TDM)

•

TDM Tributary Slots• TDM Overhead

• TDM Mapping



Summary OTN

• Management to the high bandwidth WDM network

– SDH/SONET single wavelength, OTN – multiplewavelengths

– Builds on management functionality from SDH/SONET

–

Monitoring functionality – GCC channels for management communication

• Transparency to other protocols, e.g. IP

– Wrap whatever you like

• FEC compensates physical impairments, increases cost-

efficiency• OTN switching is being deployed

• OTN transmission and switching market is increasing rapidly

optical transport network (otn)

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