A distribution port is an inlet or outlet of a product through which a particular substance can flow. 

Distribution ports are used for passage of solid, liquid, or gas substances, as well as electricity for power or communications. Flow segments (pipes, ducts, cables) can be used to connect ports across products. Distribution ports are defined by system type and flow direction such that for two ports to be connected, they must share the same system type and have opposite flow directions (one side being a SOURCE and the other being a SINK). Ports are similar to openings in that they do not have any visible geometry; such geometry is captured at the shape representation of the enclosing element or element type. Ports can have placement that indicates the position and orientation of the connection. 

Ports are assigned the distribution systems in order to indicate its role in a particular system, e.g. cold water inlet. 

The placement of a port indicates the position and orientation of how it can connect to a compatible port on another product. The placement is relative to the nesting IfcDistributionElement, IfcDistributionElementType, or enclosing IfcDistributionPort. The Location is the midpoint of the physical connection, unless otherwise indicated by cardinal point on a material profile. The Axis points in the direction of the physical connection away from the product if FlowDirection equals SOURCE (or SOURCEANDSINK or NOTDEFINED), or points opposite direction (to the product) if the FlowDirection equals SINK. 

Distribution ports are indicated on products and product types using the IfcRelNests relationship where RelatingObject refers to the enclosing IfcDistributionElement or IfcDistributionElementType respectively. The order of ports indicates logical ordering such within outlets, junction boxes, or communications equipment. Ports can be further nested into sub-ports, for indicating specific connections on components or pins. 

IfcDistributionPort can be connected to other objects as follows using the indicated relationship:

• IfcDistributionPort (IfcRelConnectsPorts) : Indicates a connection to another port having the same type and opposite flow direction. For port connections between elements, the RelatingPort is set to a port having FlowDirection=SOURCE and the RelatedPort is set to a port having FlowDirection=SINK. For aggregation scenarios, ports on a device can be mapped to aggregated devices within, in which case ports on the outer device indicate a single FlowDirection but have an additional connection internally to a port on an aggregated inner device. Refer to IfcUnitaryEquipment for an example.
• IfcDistributionElement (through IfcRelConnectsPortToElement): For dynamic ports, indicates the containing element.

The next image illustrates distribution port connectivity. 

The IfcDistributionPort can be assigned to the following entities using relationships as indicated:

• IfcDistributionSystem (through IfcRelAssignsToGroup): Indicates a system containing interconnected devices.
• IfcPerformanceHistory (through IfcRelAssignsToControl): Indicates real time or historical information captured for the device.

changes 

• IFC4 changes: IFC4 CHANGE: Ports are now related to products and product types using the IfcRelNests relationship;

use of IfcRelConnectsPortToElement is now reserved for dynamically attached ports (such as drilling a hole in a tank).