Link Attributes
Link attributes: A concatenated link usually includes a number of spliced factory lengths of optical fibre cable. The characteristics of factory lengths are given in § 6. The transmission parameters for concatenated links must take into account not only the performance of the individual cable lengths but also the statistics of concatenation.
The transmission characteristics of the factory length optical fibre cables will have a certain probability distribution which often needs to be taken into account if the most economic designs for the link are to be obtained.
Link attributes are affected by factors other than optical fibre cables, by such things as splices, connectors, and installation.
Attenuation:
Attenuation of a link:
The attenuation A of a link is given by:
A = α L α S x α C y
where: α : typical attenuation coefficient of the fibre cables in a link
α S : mean splice loss
x : number of splices in a link
α C : mean loss of line connectors
y : number of line connectors in a link (if provided)
L : link length.
A suitable margin should be allocated for future modifications of cable configurations (additional splices, extra cable lengths, ageing effects, temperature variations, etc.). The above equation does not include the signal loss of equipment connectors. The attenuation budget used in designing an actual system should account also for the statistical variations in these parameters.
The attenuation coefficient of an installed optical fibre cable is wavelength-dependent.
Figure 1 – Assumed attenuation coefficient values for G.652.A&B cable
Figure 2 – Assumed attenuation coefficient values for ITU-T G.652.C&D cable
These attenuation coefficient values are based on the spectral results of a limited number of fibres, together with an assumption of 0.275 dB/km at 1 550 nm for the maximum attenuation coefficients and 0.210 dB/km at 1 550 nm for the minimum attenuation coefficients. Actual installed cable attenuation is statistical in nature, and these values should not be taken as specification limits on individual fibres, cable sections, or splices.