PAT (Port Address Translation) is a type of Network Address Translation (NAT) that allows multiple devices to share a single public IP address by using different port numbers. PAT enables devices to access the internet without exposing their private IP addresses. A router is a device that can perform PAT by translating the source IP address and port number of outgoing packets and the destination IP address and port number of incoming packets. A Layer 3 switch is a device that can perform basic routing functions by using IP addresses, but it cannot perform PAT or other advanced routing features that a router can.