The MPEG-2 Transport Stream (TS) has been widely accepted not only for providing digital TV services@ but also as a subnetwork technology for building IP networks. This document describes a Unidirectional Lightweight Encapsulation (ULE) mechanism for the transport of IPv4 and IPv6 Datagrams and other network protocol packets directly over the ISO MPEG-2 Transport Stream as TS Private Data. ULE specifies a base encapsulation format and supports an extension format that allows it to carry additional header information to assist in network/Receiver processing.