Artesyn ATCA-F125 Installation and Use Guide (April 2014) - Manual (Page 91)

Functional Description
ATCA-F125 (6873M Artwork) Installation and Use (6806800J94J) 91
4.11.2 BITS/SSU Support
Many facilities where the ATCA-7470 is likely to be deployed, such as central offices, will include
a central Building Integrated Timing Supply (BITS) or Source Synchronization Unit (SSU).
A BITS is typically an output-only device that provides a precision timing reference, known as
the T[3] clock, to shelf-level products that use this for synchronizing the local telecom clocks.
An SSU is similar to a BITS but can in turn synchronize itself to a linecard derived reference
known as a T[4] clock.