Objectives Of The Synchronous Digital Hierarchy - Siemens SRA 4 User Manual

1.4.1.2
SRA 4 - 6/7/8/10/11/13 GHz (WB ODU) - UMN
911-381/02C0000 - Issue 3, July 2004

Objectives of the synchronous digital hierarchy

Recommendations G.707, G.708, and G.709 describe the synchronous hierarchy, the
frame structure at the 155.520 Mbit/s STM-1 base level (synchronous transport module
1st order) and the multiplex method (mapping) for information signals that correspond
to hierarchical levels which have already been defined for plesiochronous hierarchies.
The main objectives which have been pursued during the definition of recommendation
regarding SDH are:
– definition of useable knots as a transmission vehicle to a "multivendor"
environment and
telecommunication management network);
– harmonization of two plesiochronous hierarchies, European and American,
creating a worldwide standard;
– standardization of service information contained in the overhead (OH)
Apart from these general objectives, the introduction of the SDH hierarchy offers the
opportunity to develop a new generation of transmission equipment with the following
advantages:
– compatibility between equipment of different origins, obtained through:
• standardization of line interfaces, both at the electro/optical and the frame
format level;
• use of auxiliary channels and standardized control bits, inserted into the same
multiplex frame of the main signal;
– easy access to tributary signals and simplified multiplex/demultiplex operations;
– simplification of insertion/extraction functions for tributaries into/from an aggregate
stream (drop/insert) and permutation of digital streams (cross-connect);
– cost reduction by using the possibilities offered by the synchronous frame
structure, such as:
• automatic centralized management of the transmission network;
• possibility to develop new typologies for more efficient networks in terms of
reconfiguration capability (especially in the access portion) and simplification
of the reconfiguration protocol for network protection;
• equipment integration through combining line terminal and multiplex;
• simplified structures for multiplex, ADM (add/drop multiplexer), and DCX
(digital cross-connect);
– development of systems with flexible structure which allow the installation of a new
network, including dedicated networks, MAN, B-ISDN.
Also in the ETSI environment there is an extensive activity for standardization of SDH,
with the scope to adapt this equipment to European applications through a restriction of
the options foreseen in the ITU-T environment.
the corresponding
1 - PRELIMINARY INFORMATION
management system (TMN -
1-11