INTERNATIONAL  TELECOMMUNICATION  UNION

		     ITU-T RECOMMENDATION SUMMARY


Rec. No. : G.958

Title :	Digital line systems based on the synchronous digital 
	ierarchy for use on optical fibre cables

Study Group : XV - Transmission Systems and Equipment

Version : New

Date of adoption : 1990

Notes :	


Prior to the advent of SDH the scope of the design of optical line 
systems included a large number of parameters such as transmit power 
range, receiver overload and sensitivity, line code, operating 
wavelength, operation and maintenance features, etc. This led to a 
great variety of designs, each having a specific combined 
optimization of the parameters, the only common parameters being the 
attenuation and dispersion of the optical path between points S and R. 
Those systems specified in Recommendations G.955 and G.956 provided 
only longitudinal compatibility, i.e. the possibility of parallel 
installation on the same cable route. Interconnection between two 
operators could be achieved either through joint engineering of the 
optical link, or interconnection at a hierarchical level.

Synchronous line systems described in Recommendation G.958 are 
intended to provide transverse compatibility, i.e. the possibility 
of mixing various manufacturers' equipments within a single optical 
section. This is based on compliance with bit rates, frame structure 
and detailed mappings as defined in Recommendations G.707, G.708 and 
G.709, with general characteristics and functionalities as given in 
Recommendations G.782 and G.783, and with operation and maintenance 
as specified in Recommendation G.784.

For the optical parameters of the interfaces used in synchronous 
line systems, transverse compatibility is based on compliance with 
Recommendation G.957.



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