The paper https://www.blastradius.fail/pdf/radius.pdf) explicitly states DIAMETER "never replaced RADIUS for many common use cases" and "the protocol itself offers no security when used over TCP". So unless the DIAMETER traffic is isolated or tunneled, it's arguably less secure than RADIUS/TLS.
I work in telco, too - by my read, they're not disagreeing:
Although Diameter was intended to replace RADIUS, the
protocol itself offers no security when used over TCP. As a
result, RFC 6733 suggests that Diameter messages should
be secured using TLS or DTLS; 5G has replaced Diameter
with signaling over HTTP/2 [30].
"5G completely replaced DIAMETER with signaling over HTTP/2. DIAMETER is only used in legacy systems that has not yet been updated. Early 5G can be deployed as Non-standalone (NSA) or standalone (SA). NSA means a 4G core with 5G radio while SA means both 5G core and 5G radio. NSA has a lot of severe limitations. Many networks are already SA and the rest are working on rolling out SA."
Not in the Enterprise WiFi space they haven’t, it’s ubiquitous there. Though that tends to be over trusted networks or Radsec if you’re doing it right.
No we haven't. Maybe on the planet you live on all of your vendors have GA'ed enterprise grade Diameter support, but our folks still support dozens of products that haven't.
