'''Digital Data Communications Message Protocol''' ('''DDCMP''') is a [[byte-oriented protocol|byte-oriented]] [[communications protocol]] devised by [[Digital Equipment Corporation]] in 1974<ref name="HuraSinghal2001">{{cite book|author1=Gurdeep S. Hura|author2=Mukesh Singhal|title=Data and Computer Communications: Networking and Internetworking|url=https://booksarchive.google.comorg/books?id=BViV0PoH_voC&pgdetails/datacomputercomm0000hura|url-access=PA483registration|date=28 March 2001|publisher=CRC Press|isbn=978-0-8493-0928-1|page=[https://archive.org/details/datacomputercomm0000hura/page/483 483]|quote=Digital Equipment Corporation (DEC) developed a byte-oriented protocol known as digital data communications message protocol (DDCMP) in 1974.}}</ref> to allow communication over [[Network_topology#Point-to-point|point-to-point]] network links for the company's [[DECnet]] Phase I network protocol suite. The protocol uses full or half [[Duplex (telecommunications)|duplex]] [[Synchronization|synchronous]] and [[Asynchronous communication|asynchronous]] links and allowed errors introduced in transmission to be detected and corrected. It was retained and extended for later versions of the DECnet protocol suite. DDCMP has been described as the "most popular and pervasive of the commercial byte-count data link protocols".<ref name="Barksdale2013">{{cite book|last=Barksdale|first=William J.|title=Practical Computer Data Communications|url=https://books.google.com/books?id=GTrrBwAAQBAJ&pg=PA185|date=13 March 2013|publisher=Springer Science & Business Media|isbn=978-1-4684-5164-1|page=185|quote=DEC Digital Data Communications Message Protocol (DDCMP)... is the most popular and pervasive of the commercial byte-count data link protocols.}}</ref>
