The FIX protocol has been used since 1992. By understanding FIX, which is a string-based protocol, you will be able to understand other protocols. Nasdaq uses the direct data feed, ITCH and the direct-trading OUCH protocol. These protocols are much faster than the FIX protocols because of their limit overhead. These protocols use a fixed offset to specify the tag values. For instance, instead of using 39=2, the OUCH protocol will use a value of 2 at an offset of 20.

The New York Stock Exchange (NYSE) uses UTP Direct, which is similar to the NASDAQ protocols. The cryptocurrency world uses HTTP requests while using the RESTful API or Websocket way of communicating. All of these protocols provide us with different ways to represent financial exchange information. They all have the same goal: price update and order handling.