1. The Optical Transport Network (OTN) – G.709

2. Content ● Introduction ● Why OTN? ● Advantages ● Interfaces
● Properties
○ Architecture and Overhead
○ TCM
○ FEC
● Testing
● The future of OTN

3. 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)

4. 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

5. 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.

6. 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.

7. OTN Interfaces
● Inter-Domain Interfaces (IrDI) ● Intra-Domain Interfaces (IaDI)

8. OTN Architecture

9. OTN Layers (End-to-End View)

10. Optical Channel Structure
● Optical channel OH contains OPU + ODU + OTU + FAS. ● Client signal could be of any existing protocol such as IP, ATM.

11. Optical Channel Payload Unit (OPU)
● provide information on the type of signal transported. ● PSI = Payload Structure Identifier ● PT = Payload Type

12. Optical Channel Data Unit (ODU)
● allows the user to support Tandem Connection Monitoring, Path Monitoring, Automatic Protection Switching, Fault type and Fault location.

13. Tandem Connection Monitoring (TCM)

14. Optical Transport Unit
● Specifies frame alignment and FEC (Forward Error Correction)

15. Forward Error Correction (FEC)
● Enables correction and detection of errors ● Uses Reed-Solomon coding, RS(255, 239) ○ byte interleaved

16. FEC
● detects 16 bit errors, corrects 8 bit errors.

17. 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

18. 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

19. 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.

20. Testing
● Mapping/Demapping testing ● FEC testing

21. The future of OTN
● management functionality to DWDM networks ● Full backward compatibility ● Full transparency ● enables operators to operate efficiently and economically.

22. References
“G The Optical Transport network (OTN)”, Schubert, Andreas; JDSU, Pages: Optical Transport Network (OTN) Tutorial, ITU-T OTN Overview , Radhakrishna Valiveti, System Architecture Group, Infinera Corp.

23. Thank You !