Point to point is a network respectively a connection between two participants. It is the simplest topology, but also the one with the most limitations.

In point-to-multipoint topologies, one site communicates with multiple other sites. The other sites do not communicate with each other. All data flow between sites flows through a central site, also known as the root.

In multipoint-to-multipoint topologies, each site is connected to all sites. The data flow does not go through a central instance. One site can communicate with all other sites simultaneously.

Pairwise keys and group keys

There are different approaches to structuring key allocation and key usage: as a pair, where a different key is used between two parties for each direction, and as a group, where the same key is used within a group. 

Point-to-Point

For point-to-point connections it then looks like this:

For point-to-multipoint topologies, you can use either a pairwise key system or a group key system. A bidirectional group key system considers the entire network as a single group. Each site is part of that group and everyone in that group uses the same key. An undirectional group key system restricts group membership to a site's outgoing connections. All of a site's outgoing connections together form a group and use the same group key. Since each site has outgoing connections, there are multiple groups.