Trading Options Offered by ATSs
The range of operational models, services and order types provided by ATSs is broad and continues to evolve. While they were historically characterized as either call or auction markets, ATSs also include matching or market making systems, crossing networks, dark pools or some combination of these, with overlapping services and various enhancements and distinguishing features. 
Some of the main operational characteristics of ATSs can be described as follows4: