32.Recommendation G.956

1.














                             FIGURE











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 classification 
1", defined in Recommendation G.921. Recognizing that systems are  required  to
meet a "degraded minute" threshold of at least 110-6, and that future  systems
should be capable of meeting a  "degraded  minute"  threshold  of  110-7,  the
transmitter and receiver shall be designed so that a BER not worse than 110-10 is 
obtained when operating over an optical path between points S and R corresponding to 
the relevant 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 compared to the dispersion range of 1270 - 1340 nm 
quoted in Recommendation 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 suitability 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 + chromatic) is assumed to be  measured
with an optical source having a maximum 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 wavelength to less than 300 ps/nm. This can  be
achieved by confining the system operating wavelength to a reduced wavelength range 
close to the fibre dispersion zero.

4.8

























































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.