Building Integrated Timing Supply (BITS), also called Building Integrated Timing System, is a method for distributing a precision clock among telecommunications equipment.
Synchronous networks depend on accurate timing. As the number of bits per second increases, the time in which to look for any particular bit decreases. Getting network elements to agree on timing becomes more difficult at higher speeds. Synchronous networking is largely about distribution of accurate timing relationships.
Synchronous communications do not depend on start and stop flags to mark the beginning and end of meaningful data. Instead, the network constantly transmits data and uses a separate clock signal to determine when to examine the incoming stream to extract a bit. Distributing clock information to network nodes is one of the major challenges for synchronous network designers. Three major types of timing are used on networks: asynchronous, synchronous, and plesiochronous.