What is the difference between ISI access and direct DOT access? Can you also explain what the best connection for trading NYSE Listed stocks, would DOT be the best?
Both ISI and DOT go to the NYSE specialist. The difference is the technology used to send the order. NYSE orders must be sent by a NYSE member. Many clearing firms (e.g Penson) are not members so they send the orders through another party. In this case ISI orders go through AMB AMBRO's (large clearing firm and NYSE member) FIX message system. DOT orders also must go through a member. However my understanding is that the DOT system is superior to ISI since it doesn't need to go through the FIX system which can slighly slow down or lock up an order in some case. Also - with the DOT system you can send complex basket orders - you can't through ISI because of the FIX engine.