The Optical Transport Network (OTN) – G.709

Content ● 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

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