The present document outlines requirements for timing devices called Synchronization Supply Units for local node
applications (SSU-Ls). This SSU is used in synchronizing network equipment in the Synchronous Digital Hierarchy
(SDH) transport network, in the Public Switched Telephone Network (PSTN) and in the Public Land Mobile Networks
(PLMN) for local node applications.
The last SSU in a Synchronization chain, irrespective of the traffic network, provides the applications for this type of
clock.
NOTE: The requirements in the present document apply under environmental conditions according to one of the
environmental classes defined in ETS 300 019 [1], unless stated otherwise. The manufacturer will need to
specify to which specific environmental class the equipment belongs.
A description of the Synchronization Supply Unit (SSU) logical function is given in figure 1 in EN 300 462-2-1 [3]. In
general, the SSU will have multiple timing reference inputs and in the event that all timing references fail, the SSU
should be capable of maintaining operation (holdover) within prescribed performance limits as detailed in the present
document. The requirements laid down in the present document describe the minimum performance of an SSU applied
as a local node clock (SSU-L). Requirements for transit node clock applications for SSUs are described in
EN 300 462-4-1 [5].
The SSU-L function can be implemented in a separate piece of equipment called a Stand-Alone Synchronization
Equipment (SASE) or it can form a logical function of another equipment such as a telephony exchange or an SDH
cross-connect.
The requirements specified in the present document refer to the design of new synchronization networks and
consequently they do not necessarily represent the performance of existing synchronization network and equipment.
A timing device within SDH equipment can also conform to EN 300 462-5-1 [6].
The characteristics r (...abbreviated)