# Calculation of Dispersion Limited Transmission Distance

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The principle of dispersion is complicated. However, it is easy to calculate the dispersion-limited transmission distance, and the transmission distance with limited dispersion is calculated.
Formula:

Ld=ε/ Dm (This formula does not need to be explained.)

In the preceding information: Ld: Transmission distance

ε – Dispersion Tolerance of the Light Source

Dm- Dispersion value per kilometer

The unit of the dispersion value is ps/(nm*km), which indicates the delay of each wavelength in the unit wavelength spacing. The dispersion tolerance unit is ps/nm, which is determined by the light source.

For example, ε=1600 ps/nm, Dm=20 ps/(nm*km), then Ld equals 1600.ps/nm /2020
ps/(nm*km)=80 km: If the fiber dispersion effect is considered, a maximum of 80 km signals can be transmitted. If the distance exceeds 80 km, dispersion compensation is required. Dispersion compensation is equivalent to ε compensation. Generally, the specifications of the dispersion compensation module are represented by kilometers.

The maximum transmission distance of a device must meet the preceding two restrictions. The transmission distance must comply with the bucket theory. The maximum transmission distance depends on the minimum distance between two factors. If the transmission distance does not meet the requirement, compensation is required.

The OTN ransmission distance calculation is much more complex than that of the SDH and packet network. The OTN is not involved in the related work. In the case of the OTN, the parameters of each segment are adjusted and a certain margin is reserved, in most cases, O****ransmission distance calculation is not involved. For details, see related documents.

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