Of all the changes in fixed or mobile network architectures over the past few decades, one of the notable physical layer changes is the application of optical fiber more densely in distribution and access networks.
But also noteworthy is the disappearance of switching or computing locations as demarcation points.
In the past, we could always demarcate the access network from the distribution network at a central office or rermote terminal location. That makes less sense these days, as processing is increasingly distributed.
Both fixed and mobile networks use similar architectures in the core network, diverging mostly in the access network. Core network transport these days always uses optical fiber media. Transport networks (sometimes known as distribution networks) that move traffic from the access network to the core network also are commonly based on optical fiber platforms.
Access networks that move traffic from customer sites to transport aggregation points rely on different media (cable versus wireless radios).
The other common change is that both fixed and mobile networks can be described without reference to places where processing operations occur. In virtualized and distributed networks, that can happen at many different places.
In past days transitions between portions of the network would happen at processing locations such as central offices, which traditionally terminated the access network. These days, processing no longer is a consistent demarcation point between network segments (core, transport/distribution and access).