The key technology of XG-PON: Physical Medium Dependent (PMD) layer

Line rate knowledge

  XG-PON defines two line rate levels, which are:

  • XG-PON1—–downstream 10Gbps, uplink 2.5Gbps;
  • XG-PON2—–downstream 10Gbps, uplink 10Gbps.

  The current standard only defines the physical layer performance indicators for XG-PON1, and the detailed characteristics of XG-PON2 have not been collected.
  The downlink signal nominal line rate of XG-PON1 is 9.953 28Gbps, and the nominal line rate of the uplink signal is 2.488 32Gbps. The defined parameters are classified according to the uplink signal and the downlink signal. The nominal line rate is shown in the following table.

 Transmission directionNominal line rate
XG-PON1Downstream9.95328
Upstream2.48832

  When the OLT and the end office work in the running state, the rate of the downlink signal should track a level 1 clock (the precision is 1*10^(-11), defined); when the OLT works in the free-running mode, the accuracy of the downlink signal should be At least one level 4 clock (accuracy is 3.2*10^(-5), defined); if the OLT carries timing-sensitive services, such as mobile backhaul, the accuracy of the downlink signal should be a 3-level clock (accuracy is 4.6) *10^(-6), defined). When the ONU is running and authorized, it should send the same signal as the downstream signal clock it received.

XG-PON Working wavelength

  The downstream wavelength range of the XG-PON1 on the single fiber system is 1575 to 1580 nm (for the outdoor type range is 1575 to 1581 nm), and the upstream wavelength range is 1260 to 1580 nm. As shown in the following figure, the wavelength assignment parameters in the figure are shown in the following table. .

XG-PON system wavelength distribution map (FOT Blog)

ItemSymbolUnitValueApplication
XG-PON uplinkFor XG-PON uplink
Upper Boundnm1260
Lower boundnm1280
Enhanced band (option 1)For GPON uplink (wavelength band: 1290~1330nm)
Upper Boundλ1nm1290
Lower boundnm1330
Enhanced band (option 2)Reserved. Note: The attenuation of optical splitters (in accordance with ITU-T G.671) and optical fibers (in accordance with ITU-T G.652 A/B) is not guaranteed in this band.
Upper Boundnm1360
Lower boundnm1480
Enhanced band (option 3)For GPON downlink (1480 ~ 1500nm) and / or video signal distribution (1550 ~ 1560nm) *1
Upper Boundnm1480
Lower boundnm1560
XG-PON downlink (Basic band)For XG-PON Downlink *2
Upper Boundnm1575
Lower boundnm1580
Enhanced band (option 4)Reserved. Note: The selection of the upper bound value should take into account the following factors: increased bending loss of the fiber at long wavelengths; loss of the filter used to separate/in combination with the monitoring signal and the user signal
Upper Boundλ5nmTBD
Lower boundλ6nmTBD to 1625
*1 Note: Appropriate guard bands should be considered when using multiple wavelengths in the same enhancement band; *2 Note: The OLT for outdoor use is allowed to use the 1575 to 1581 nm range.

Optical power budget

  When deploying B+-type ODN (which can coexist with the same ODN as the GPON of the B+ optical power budget), considering the additional loss introduced by WDM1r, XG-PON defines two optical power budget levels:

  • N1—–the nominal maximum attenuation between the two IFXG-PON reference points is 29dB;
  • N2—–The nominal maximum attenuation between the two IFXG-PON reference points is 31dB.

  When deployed in a C+ class ODN, the XG-PON defines an extended optical power budget level.

Physical Medium Dependent (PMD) layer parameters

  The main optical interface parameters in the 9.95328Gbps downstream direction are as follows:

  • Nominal line rate: 9.95328Gbps;
  • Working wavelength: 1575 ~ 1580nm;
  • Line code: NRZ;
  • Minimum extinction ratio: 8.2dB;
  • Transmitter reflected light power tolerance: >-15dB;
  • Maximum reflection of the device measured at the receiver wavelength: <-20dB

  More detailed parameters, please consult our engineers.

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