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: 1-14http://www.item.ntnu.no/fag/ttm1/misc/g709otn_wp_opt_tm_ae.pdf

Optical Transport Network (OTN) Tutorial, ITU-Thttp://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 !