scope:

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 SSU's 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 related to holdover and noise generation performance make this type of clock also suitable for application in the GSMradio sub-system (see TS 100 912 [7]). In particular as a clock used by a Base Station Controller (BSC) or by a Mobile Switching Centre (MSC), further synchronizing (typically via a traffic link) the Base Station (BS). The characteristics of this clock are not optimized for a clock to be implemented in the BS.

In order to fulfil the frequency accuracy requirements required in the GSM radio interface, this clock should be connected to a synchronization network that is properly designed and correctly operating.