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The Optical Transport Network
(OTN) – G.709
● Introduction
● Why OTN?
● Advantages
● Interfaces
● Properties
○ Architecture and Overhead
○ TCM
○ FEC
● Testing
● The future of OTN
Introduction
● OTN = The Optical Transport Network
○ specified in ITU-T G.709 standard
● ITU-T definition:
“a set of Optical Network Elements connected by optical
fiber links, able to provide functionality of transport,
multiplexing, switching, management, supervision and
survivability of optical channels carrying client signals.”
● aim is to enable the multiservice transport of packet based
data and legacy traffic (Next generation SONET/SDH)
Why OTN?
● Operators’ need to use existing fiber to satisfy Growing
demand for services and bandwidth
● DWDM increased fiber bandwidth, but lacked protection
and management capabilities.
● OTN Combines the benefits of SONET/SDH with
DWDM
Advantages
● Protocol transparency
○ Integrity of the client signal is maintained.
○ End user views exactly what was transmitted.
● Backward compatibility for existing protocols.
● Better switching scalability
○ OTN is able to switch at a higher bit rates than SDH.
Advantages
● Better Forward Error Correction (FEC)
○ G.709 FEC algorithm result in up to 6.2 dB improvement
in Signal to Noise Ratio (SNR).
○ Increased span length
○ Can increase number of channels
○ an enabler for transparent optical networks
● Tandem Connection Monitoring (TCM)
○ Unlike SDH, OTN has six TCM fields.
○ Allowing each network to be monitored.
OTN Interfaces
● Inter-Domain Interfaces (IrDI)
● Intra-Domain Interfaces (IaDI)
OTN Architecture
OTN Layers (End-to-End View)
Optical Channel Structure
● Optical channel OH contains OPU + ODU + OTU + FAS.
● Client signal could be of any existing protocol such as IP,
ATM.
Optical Channel Payload Unit (OPU)
● provide information on the type of signal transported.
● PSI = Payload Structure Identifier
● PT = Payload Type
Optical Channel Data Unit (ODU)
● allows the user to support Tandem Connection Monitoring,
Path Monitoring, Automatic Protection Switching, Fault
type and Fault location.
Tandem Connection Monitoring (TCM)
Optical Transport Unit
● Specifies frame alignment and FEC (Forward Error
Correction)
Forward Error Correction (FEC)
● Enables correction and detection of errors
● Uses Reed-Solomon coding, RS(255, 239)
○ byte interleaved
FEC
● detects 16 bit errors, corrects 8 bit errors.
Benefits of FEC
● Gain in power level.
● Network operator can accept a lower quality signal
● Reduction in the use of 3R regenerators
● Early warning capabilities
Optical multiplex section(OMS)
● consists of multiplexed OChs
Optical transmission section (OTS)
● transports the optically multiplexed sections
● perform monitoring and maintenance between
optical network elements
Testing
● To guarantee bandwidth availability and quality
● introducing alarms and errors in the system and
measuring their effects on the transmission
● E.g. stimulus testing, mapping/demapping testing,
FEC error testing.
Testing
● Mapping/Demapping testing
● FEC testing
The future of OTN
● management functionality to DWDM networks
● Full backward compatibility
● Full transparency
● enables operators to operate efficiently
and economically.
References
“G.709 - The Optical Transport network (OTN)”, Schubert, Andreas; JDSU,
Pages: 1-14
http://www.item.ntnu.no/fag/ttm1/misc/g709otn_wp_opt_tm_ae.pdf
Optical Transport Network (OTN) Tutorial, ITU-T
http://www.itu.int/ITU-T/studygroups/com15/otn/OTNtutorial.pdf
OTN Overview , Radhakrishna Valiveti, System Architecture Group, Infinera Corp.
https://www.infinera.com/technology/files/infinera-IEEE-OTN-Overview.pdf
Thank You !