The Federation Substrate consists of all of the AAA entities. In some cases, the AAA proxies may not exist, as the AAA client can talk directly to the AAA server. Specifications such as the Trust Router Protocol (https://www.ietf.org/proceedings/86/slides/ slides-86-rtgarea-0.pdf) and RADIUS dynamic discovery [RFC7585] can be used to shorten the path between the AAA client and the AAA server (and thus stop these AAA proxies from being observers); however, even in these circumstances, there may be AAA proxies in the path.