The UPA Development and API Concept guides mention qualified streams, but do not contain any details of what they are for and how they can be used.
Qualified streams add TR implemented behaviors on top of a private stream's functionality to give us a tunnel stream. The private stream foundation causes the stream to go through TREP and cascaded components to create a stream between the two end points. The qualified stream negotiates desired behavior information and then provides it over the stream after negotiation. Some examples of qualified stream behaviors are authentication (e.g. end to end log-on), end to end reliable delivery, end to end flow control, and guaranteed message delivery with a QProvider. The qualified stream and the behaviors currently associated with it were released in UPA 8.0 and are available in UPA8.X/ETA 3.X for C and Java as well as EMA C++. It will be released in EMA Java shortly.
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Qualified streams are used by Tunnel Streams, a feature for end-to-end communication over a stream. See the Value-Added Components Guide for details and the Reactor's API for the feature.