By leveraging the Transport API Value Added Reactor, the Enterprise Message API allows users to create and use special tunnel streams. A tunnel stream is a private stream that has additional behaviors associated with it, such as end-to-end line of sight for authentication and reliable delivery. Because tunnel streams are founded on the private streams concept, these are established between consumer and provider endpoints and then pass through intermediate components, such as LSEG Real-Time Distribution System or the LSEG Real-Time Edge Device.
The user creating the tunnel stream sets any additional behaviors to enforce, which Enterprise Message API sends to the provider application end point. The provider endpoint acknowledges the creation of the stream as well as the behaviors it will enforce on the stream. Once this is accomplished, negotiated behaviors are enforced on the content exchanged via the tunnel stream.
The tunnel stream allows for multiple substreams to exist, where substreams flow and coexist within the confines of a specific tunnel stream. In the following diagram, imagine the tunnel stream as the orange cylinder that connects the consumer application and the Provider application. Notice that this passes directly through any intermediate components. The tunnel stream has end-to-end line of sight so the Provider and Consumer are effectively talking to each other directly, although they are traversing multiple devices in the system. Each of the black lines flowing through the cylinder represent a different substream, where each substream is its own independent stream of information. Each of these could be for different market content, for example one could be a Time Series request while another could be a request for Market Price content.