Internet Standards/CD2.mdf/ccitt/1992/g/g956.asc

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32.    Recommendation G.956



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2.    Type of transmission medium





































FIGURE













4.1





















    The digital line systems described in this Recommendation are required
to provide error performance in accordance with "section quality classifi-
cation 1", defined in Recommendation G.921. Recognizing that systems
are required to meet a "degraded minute" threshold of at least 1_10-6,
and that future systems should be capable of meeting a "degraded
minute" threshold of 1_10-7, the transmitter and receiver shall be
designed so that a BER not worse than 1_10-10 is obtained when operat-
ing over an optical path between points S and R corresponding to the rel-
evant values given in Table 1/G.956 for multimode fibre systems and
Table 2/G.956 for single-mode fibre systems.













































Note - For single-mode systems operating in the 1300 nm range, the
lower wavelength limit is determined from consideration of dispersion
and cut-off wavelength effects, while the upper wavelength limit is due to
consideration of dispersion and attenuation. In particular it should be
noted that the range quoted in this Recommendation is restricted com-
pared to the dispersion range of 1270 - 1340 nm quoted in Recommenda-
tion G.652 because of the possibility of OH peak related excess losses.
To ensure satisfactory system operation, the cut-off wavelength of the
shortest length of cabled fibre in a single-mode elementary cable section
must not exceed the operating wavelength. The second order (LP11)
mode should be sufficiently attenuated along the fibre such that at the
detector modal noise and bimodal dispersion effects are negligible.

4.6











    The calculation of attenuation between points S and R should consider
the variation of the optical fibre loss over the actual wavelength range of
the optical source.













































































Note 1 - The description of the baseband response with a single value
(the -3 dB optical bandwidth) may not be sufficient to determine the suit-
ability of the fibre for the specified system. A quasi Gaussian impulse
response may be assumed for design purposes but a more detailed
description of the fibre response may be necessary in some cases.



Note 2 - In the case of LED systems for the values given in the table the
optical fibre is assumed to have a nominal numerical aperture of 0.20-
0.21. Additionally, the overall -3 dB optical bandwidth (modal + chro-
matic) is assumed to be measured with an optical source having a maxi-
mum linewidth (FWHM) of 60 nm and 100 nm centred at 850 nm and
1300 nm respectively.

4.7









    The calculation of attenuation between points S and R should consider
the variation of the optical fibre loss over the actual wavelength range of
the optical source.























































































Note 3 - This value indicates the maximum permissible dispersion
for           139 264 kbit/s systems at the limit of the operating wavelength
range specified (1270 - 1330 nm). To optimize the system design it may
be necessary to limit maximum dispersion at the system operating wave-
length to less than 300 ps/nm. This can be achieved by confining the sys-
tem operating wavelength to a reduced wavelength range close to the
fibre dispersion zero.



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8.2

























































































ANNEX B











































































33.    Supplement No. 11 - Data on cable ships and submersible equipments
of various countries. (Referred to in section 6.3 of Fascicle III.2,
amended at Melbourne, 1988.)



    The text of Supplement No. 11 has not been included in the final report,
but will be printed in the Blue Book at the appropriate place.