1 - PRELIMINARY INFORMATION
1-25
SRA 4 - 6/7/8/10/11/13 GHz (WB ODU) - UMN
911-381/02C0000 - Issue 3, July 2004
1.4.2
SDH transmission network
1.4.2.1
General description
The benefits introduced by the new synchronous SDH hierarchy allows to predict an
evolution of transmission networks toward flexible structures with dynamic
reconfiguration capability and monitoring and supervision functions, controlled by an
efficient management system (TMN = telecomunications management network).
The fundamental knots of this architecture are replaced by network elements (NE =
network elements) with flexible drop/insert functions and, more generally,
cross-connect.
The SDH transmission equipment can be divided into two groups:
–
Line repeaters with regeneration functions which communicate at the RSOH level,
in other words at the lower level of the section status. The use of regenerators is
limited to long distance connections and a very limited number of cases in urban
and connection networks.
–
Terminal knots which change and elaborate the incoming information stream. They
often also include the multiplex function of digital structures in the STM-N frame,
evidencing typical characteristics of SDH network elements, such as the fact that
there is no distinction between multiplex frames and line signal, this way allowing
an integration of the equipment. For this reason, these terminals also a function as
a terminal at the section level (managing also the SOH).
The following equipment represents terminal knots:
–
MUX both in a terminal and an add-drop (ADM) configuration, which provide
flexibility in the access area (both TU and AU);
–
DXC-TU (Digital Cross-connect Tributary Unit), which provides flexibility for the
transit of already synchronized streams in the network;
–
DXC-AU (digital cross-connect administrative unit), used preferably for network
protection and therefore located in centers with higher hierarchical levels.
Fig. 1.12 shows an example of the SDH network, implemented with the above
mentioned equipment.
