The most basic network topology is a point to point link where two sites are connected by one or more modems. The modem connections can take multiple forms depending on the intent and traffic type of the link.

An example diagram of this type link is shown below with one common interface type. In this example a point to point link connects two routers via various synchronous serial interface types. The routers in this case are examples of DTE equipment and could be replaced by audio, video or other communications gear.

One interesting variation is the use of a router on one end with any of the shown interfaces and a "SnIP" IP interface in the modem on the other link end. The SnIP Router link mode is capable of inter-operating with a Cisco router using the Cisco HDLC protocol, including use of standard Cisco keep-alive messages.

Yet another possible point to point IP network configuration is the use of external routers as shown above but interfacing with the modems via a SnIP on each end. The SnIPs in this type connection would be placed normally into Bridge link mode.