NBMA essentially describes the functionality of a network at Layer 2. An NBMA network is:
- non broadcast - which means that communication can only occur from one host to another. Broadcast and multicast are not inherently supported.
- multiple access - multiple hosts share the same medium
In contrast, Ethernet is multiple access, but inherently supports broadcast communication.
For NBMAs, data is transmitted only directly from one host to another single host over a virtual circuit or across a switched fabric. Although not inherently supported, multicast and broadcast can be simulated by creating multiple unicast communications to create what are known as pseudo-broadcasts.
Once again, the NBMA operation is a Layer 2 phenomenon. You can run IP over NBMA networks and if configured correctly, IP operation will take place and will not know the difference. The only thing you may need to adjust is the split horizon rule for dynamic routing protocols.
Typical examples of NBMAs include ATM, Frame Relay, X.25 as well as home power line networks. As you can see from this list of technologies, apart from DMVPN, NBMA networks do not have an extensively wide application base, and are primarily older technologies that are on their way to being phased out. Nevertheless, there are still enough NBMA networks to warrant a good understanding of the mechanisms involved.
I hope this has been helpful!