Compatibility of multivendor Dense Wavelength Division Multiplexing System Master Thesis Jan Waldén, Helsinki Supervisor PhD Timo Korhonen

Table of contents Optical characteristics Optical Signal to Noise Ratio Polarisation Mode Dispersion Chromatic dispersion Optical Transport Network Modulation Methods Forward Error Correction Test setup Test results ITU-T specifications Conclusions

Optical characteristics Transport Multiple wavelengths in one fibre. A DWDM system is today most commonly implemented in the C-band, that is between 1530nm and 1565nm. For example 1552,52nm equals 193,1 THz. Conversion from frequency to wavelength f=c/. The speed of light in the fibre is approximately two thirds of the speed of light in vacuum.

Optical characteristics Channel spacing according to ITU-T G GHz is approximately 0,8nm 50 Ghz is approximately 0,4nm 25 GHz is approximately 0,2nm 12,5 GHz is approximately 0,1nm Common channels spacings in the backbone network are the 100GHz and 50GHz spacing With 50GHz spacing the number of channels in the C-band is between 72 to 88 channels depending on the mux/demux type.

OSNR - When the OSNR is too low the BER starts to increase. - Forward Error Correction (FEC) can be used to improve the BER at low OSNR - When planning the DWDM network OSNR is the limiting factor -Amplifying the signal also amplifies the noise -3R regeneration (reamplification, reshaping, retiming) -Needed OSNR for modulation and line codes

Measuring OSNR

PMD Two orthogonal polarisation modes travel at different speed and causes pulse broadening. The refractive index is not constant at any cross sectional area of the fibre The polarisation modes will have different refractive indexes and propagate at different velocity

Chromatic dipersion Broadening of the pulse High frequencies travels faster than low frequencies Difference in the refractive index ->different velocity Intersymbol interference Mitigation of chromatic dispersion – Dispersion compensation fibre – Chirped fibre Bragg grating – Electronic dispersion compensation

Modulation methods and their weaknesses ModulationODBNRZ-DPSKRZ-DPSKDRZDP-QPSKDQPSK OSNR sensitivity [dB]0341,533,5 PMD tolerance [ps]1,82,533na8 Nonlinear toleranceWeak AverageGoodVery WeakAverage ComplexitySimpleIntermediateComplexSimpleVery ComplexComplex

OTN Client signal OPU payload Client signal OPU payload OPU ODU OTU OCh The OPU OH Added The ODU OH Added The OTU OH Added with the FEC Over head The OCh OH Added In every step the where an overhead is added the the former payload with the overhead becomes the new payload

End to end circuit MUX Transp onder MUXOA SwitchMUX Transp onder MUX Transp onder MUXOA MUX Transp onder OTS OMS OCh 3R OTU/ODU

SuperFEC ITU-T standard G.975

SuperFEC gain

M U X/ D E M U X OA DCM STM64STM64 STM64STM64 ATT2ATT2 ATT2ATT2 ATT1ATT1 ATT1ATT1 OA ATT3ATT3 ATT3ATT3 DCM ATT4ATT4 ATT4ATT4 Vendor D

Vendor C DWDM system

Test setup

Test with vendor C and B

Vendor B and C optical levels mdmd mdmd WSS OAOA OAOA OAOA OAOA OAOA OAOA OAOA OAOA GMD mdmd mdmd Loop OAOA OAOA OAOA OAOA OAOA OAOA OAOA OAOA Site XSite Y Site Z -18,6 dBm Rx -4 dBm -4,4 dBm Rx -10 dBm Tx-13,9 dBm VOA 1,6 dB OPOUT -1,7 dBm 0 dBm Out -9,2 dBm VOA 1,61 dBm VOA 0,04 dB System B System C

Test results Test1Test2Test3Test4Test5Test6Test7Test8Test9Test10Test11Test12 vendor D transponder TPT10G/TC-ERTx Fibre before Vendor C (km) Before vendor C DCM module 80 kmNo YesNoYes Vendor D OA before Vendor CNo Yes +15dB att Vendor C DWDM span (km) Fibre after Vendor C (km)0204,8 24,828,332, After vendor c DCM module 80 kmYes vendor D transponder TPT10G/TC-ERRx Total distance (km) ,8144,8164,8168,3172, Does not work ok Does not workok Does not workok Worse OSNR

G.959 DWDM interoperability with post-and pre-amplifiers

G Metro DWDM without amplifiers

Interoperability of DWDM capacity DWDM End Terminal VendorX DWDM End Terminal Vendor Y DWDM end Terminal Vendor X OCh OTU1 and OTU2 ODU1 and ODU2 According to G metro DWDM applications have a Standard OTU1 and OTU2 G.709 frame with FEC in order to enable Interoperability for Spans without lineamplifier DWDM ring Terminal VendorX OCh OTU1 and OTU2 G.698.1

Conclusion -OSNR tolerance improved with FEC. The FEC is implemented on every channel. Compatibility issue, the same FEC has to be used by the transponders in both ends. -Chromatic Dispersion DCF (compensates all channels easier to use with foreign wavelengths) or eDCO (compensates one channel) and reduces attenuation on the line restricts the use of foreign wavelengths. -Tolerances of Modulation methods, compatibility depends on which method is chosen by the vendors.

ITU-T specifications G.871 Framework for Optical Transport Network Recommendations coordination of the G.872 Architecture of optical networks G Definitions and test methods for statistical and nonlinear related attributes of single mode fibre and cable G.652 Characteristics of a single mode fibre cable G.694.1Spectral grids for WDM applications: DWDM frequency grid G Multichannel DWDM applications with single-channel Optical interfaces G.709: Interfaces for the Optical Transport Network (OTN) G.798: Characteristics of Optical Transport Network hierarchy equipment functional blocks G.957 Optical interfaces for equipment and systems relating to synchronous digital hierarchy G.959 Optical transport network physical layer interfaces G.975 Forward error correction for high bit-rate DWDM submarine systems