Address plus Port Wikipedia
The Address plus Port (A+P) approach to the IPv4 address shortage is a technique for sharing single IPv4 addresses among several users without using stateful network address translation (NAT) in the carrier network. The technique is described in experimental RFC 6346.
Normal routing only uses the IPv4 address to identify which host an IP packet is destined for. A+P uses the destination TCP or UDP port in addition to the IP address to extend the range of available host addresses. Each host is assigned a unique range of ports which they set as the source port in outbound packets and which they use to receive inbound traffic.
A+P is a stateless alternative to conventional stateful NAT, as the A+P gateway does not need to keep track of every TCP or UDP flow. However, it does require A+P aware software at the end-point, capable of limiting the range of port numbers used for originating connections to its allocated range, either in the end host, or, in the more common likely scenario, in the customer premises equipment own local NAT44 implementation.