ion speeds for the transfer of data as diverse links are utilised. Yet another advantage is the possibility of using diverse routes to transfer a message: two packets containing parts of a message may go through different paths as routers on the way to determine the next relay point. As discussed above, this redundancy was a major requirement of the US military in funding the ARPA project in the 1960s that led to the development of the internet: a com- munications system that could withstand the destruction of major switching hubs in the event of a nuclear war. 3 Post van: OSX (own work) https://commons.wikimedia.org/wiki/File%3A2000-2004_Ford_Transit_(VH)_low_ roof_SWB_van_(Australia_Post)_01.jpg. Packetised Data Communications Case Study 8.1: DHL and FedEx Packet-switched Networks An early application for packet-switched networks was document transmission using facsimile (fax) machines. The invention of modern fax machines is credited to Xerox Company and its Long Distance Xerography (LDX) in 1964 and improved Magnafax in 1966. These were analogue image transmission systems and on average took 6 min to transmit a document page. In the mid-1960s Hochman and Weber, two scientists from Lockheed who had worked on digital image compres- sion techniques for space probe telecommunications, founded Dacom to commer- cialise digital fax machines. Their digital fax machines connected to telephone lines and used in-band frequency tones to send digital signals. Digital fax improved on Xerox technology and could transmit a document page in less than 1 min. By the late 1970 many companies were making fax machines, prominently three Japanese companies: Canon, Ricoh and Konica. These early fax machines however were quite heavy and expensive and beyond what most companies needed or could afford [5, 6, 7, 8]. Courier and overnight document delivery companies felt threatened by this new mode of document delivery and started their own fax services. Two courier com- panies, DHL and FedEx, used the nascent packet-switched networks to