The Stream Portal block offers a local machine stream IO (similar to the HTTP block) but is much more efficient and includes an adjustable buffer for time critical missions.
In some cases the HTTP blocks offer not enough speed and a too high time delay e.g. if you want to stream the Rx IQ data directly to the Tx to build a signal loop. In this case you can use the Stream Portal blocks instead which is much more efficient since it does not struggle with the HTTP socket.
In addition you can adjust the buffer (via the stream delay time) by up to +/- 1s in fractions of 1 ns