Ethernet-over-PDH (EoPDH) is a collection of technologies and standards that allow the transport of native Ethernet frames over the well-established Plesiochronous Digital Hierarchy (PDH) telecommunications infrastructure. This enables carriers to make use of the extensive network of legacy PDH and SDH equipment to provide new Ethernet-centric services. In addition, EoPDH paves the pathway for interoperability and the gradual migration of carriers to Ethernet networks. This application note covers the technologies used in EoPDH, including frame encapsulation in GFP as defined in G.7041, mapping Ethernet-over-PDH framing, link aggregation through G.7043, link-capacity adjustment through G.7042, management messaging as defined in Y.1731 and Y.1730, VLAN tagging, QoS prioritization, and higher layer applications such as DHCP servers and HTML user interfaces.