Short answer
DIA is a managed enterprise internet service for offices and core sites. IP Transit is a wholesale service for organisations that run their own network and want full control of routing using BGP.
In detail: IP Transit vs Dedicated Internet Access (DIA)
The deciding question is who runs the routing. With DIA, FirstNet does: you receive a fully managed Layer 3 internet service with static public IPs, enterprise routing, dedicated 1:1 contention and symmetric committed bandwidth, delivered over approved fibre. With IP Transit, you do: your Autonomous System gets access to the global routing table through FirstNet's upstream and peering ecosystem, and you set routing policy and traffic engineering yourself.
IP Transit fits if you:
- Hold a public ASN and run a router with BGP v4
- Are an ISP or WISP, a hosting, cloud or data centre operator, a CDN, or an enterprise with in-house network engineering
- Want to multi-home across several upstreams
- Need uncontended, capacity-based transit
Choose DIA if you want FirstNet to manage the service end to end for a head office, data centre or other critical site. The support boundaries differ too: IP Transit support covers FirstNet's transit domain, backbone and ports, while your routing policy remains your responsibility.
Source: FirstNet Carrier-Grade ISP Infrastructure service page →