The '''Transaction Protocol Data Unit''' ('''TPDU''') is a [[Packet switching|packet-based]] [[Protocol (science)|protocol]] originally designed for financial [[Financialfinancial transaction|transaction]] processing over an [[X.25]] [[telecommunications network|network]].<ref>{{citation |title=TPDU - The Transaction Protocol Data Unit |url=https://www.eftlab.com/index.php/site-map/our-articles/295-tpdu-the-transaction-protocol-data-unit/ |access-date=20192021-0503-0626}}</ref><ref>{{citation |title=TPDU Protocol |url=http://www.vanguardnetworks.com/Collateral/Documents/English-US/102_12.pdf |access-date=2019-05-06}}</ref>
