Because nodes in DTN might be interconnected using more than one type of underlying network technology, a DTN is best described abstractly using a multigraph. Edges in this graph are, in general, time-varying with respect to link capacity, delay. When an edge has zero capacity, it is considered to not be connected.
Because deges may vary between positive and zero capacity, it is possible to describe a period of time(interval) during which the capcity is strictly positive, and the delay and capacity can be considered to be constant. This period of time is called a “contact”.
The product of the capacity and the interval is known as a contact’s “volume”.
Types of Contact [RFC4839 Section 3.8.1]
- Persistent contacts
(DSL,Cable Model connection)
- On-Demand Contact
(Dial-up connection)
- Intermittent-Scheduled Contacts
(low-orbit satellite)
- Intermittent-Opportunistic Contacts
(infrared or bluetooth communication link between a person digital assitant and a kiosk in an airport concourse)
- Intermittent-Predicted Contacts