Subscribers applications, which can be desktop, web portal or black box based, will communicate with the market center servers using different types of messages. These messages are made available through the WebSocket API layer. The API messages are backward and forward compatible. New messages and new fields can be added to the API but existing messages and fields will never change so users of previous API versions will not be affected when new versions are released. If a subscribers wants to access to new messages or fields, they can simply them to their message structure. Most of messages and related fields are self-explanatory.