Trigger throttling system for CMS DAQ

This document is a first attempt to define the basic func-tionnalities of the TTS in the CMS DAQ. Its role is to adapt the trigger pace to the DAQ capacity in order to avoid congestions and overflows at any stage of the readout chain. The different possibilities for the TTS to measure the load on parts of the chain are examined. It clearly appears that one part of the chain needs fast reaction time (few tens of microseconds) whereas the rest of the chain can afford longer reaction time, available to nowadays processors.