  Recent improvements in Extended Reality (XR) technology created an increase
in XR products and solutions in the industry, while raising new requirements
for new or improved architectural concepts. This need can be particularly
complex as XR applications often relate both to 3D geometric rendering and
multimedia paradigms. This paper outlines the main concepts relevant to XR,
both from a game engineering and multimedia streaming system perspective. XR
requires new metadata and media/game orchestration to allow complex interaction
between users, objects, and (volumetric) multimedia content, which also results
in new requirements on synchronisation (i.e., for global object state and
positioning). Furthermore, the paper presents the functional blocks needed in
new XR system architectures and how they will glue both (game and media) spaces
together. The discussion of functional components and architecture relates to
the ongoing activities in relevant standardisation bodies like Khronos, MPEG,
and 3GPP. To make XR successful on the long term, the industry needs to agree
on interoperable solutions and how to merge both game and media paradigms to
allow complex multi-user XR applications.
