Re: The difference is not traffic priority....
The trouble is, that quote from RFC 791 has been obsolete since RFC 2474 in 1998. That RFC is called "Definition of the Differentiated Services Field (DS Field) in the IPv4 and IPv6 Headers" and its whole point is indeed what Huawei says: give different types of traffic a service level that suits that traffic. And it isn't about precedence (or priority) - it's about delivering an audio stream with low jitter while competing with a background download, for example. And yes, horror of horrors, some services might cost more than others.