a duct is an active channel of a single standard protocol between two correlated endpoints. Ducts are stacked to be combined to form a tunnel.

Stacked - a tunnel is composed of two or more stacked ducts.

An Active Channel - Usually, we refer to a duct as a single active channel, or a single active channel that we expect to achieve.

Standard Protocols - a duct usually relates to a single protocol between two endpoints, those two endpoints are usually on different machines. They are standard stable protocols with tunable configuration.

Implied - although a duct achieves a connection with two endpoints, the two sides of a duct-specification is disconnected in practice. Both nodes must have coordinated configuration files to accomplish the creation of the duct. One side of a duct is called the duct-configuration, the implied combined configuration is the duct-specification.

Distributed and Transparent - The low-level, protocol, and implicit configuration of a duct is important. This means that each node in a dull system can operate independently and distributed. Importantly, this accomplishes transparency for customers. Any dull node that is installed within their network is literal and can be audited.