Proprietary Networks and Internetworking: 1972-1980

Proprietary Networks and Internetworking: 1972-1980

The early ARPAnet was a single, closed network. ln order to communicate with an ARPAnet host, one had to be really connected to another ARPAnet IMP. ln the early to mid-1970s additional stand-alone packet-switching networks besides ARPAnet came into being:

●  ALOHANet, a microwave network linking universities on the Hawaiian islands [Abramson 1970], as well as DARPAs packet-satellite [RFC 829] and packet-radio networks [Kahn 1978]

●  Telenet, a BBN commercial packet-switching network based on ARPAnet technology

●  Cyclades, a French packet-switching network pioneered by Louis Pouzin [Think 2009]

●  Time-sharing networks such as Tymnet and the GE Information Services network, among others, in the late 1960s and early 1970s [Schwartz I977]

●  IBM's SNA (1969-1974), which paralleled the ARPAnet work [Schwartz 1977]

The number of networks was increasing. With perfect hindsight we can see that the time was ripe for developing an encompassing architecture for connecting networks together. Pioneering work on interconnecting networks (under the sponsorship of the Defense Advanced Research Projects Agency (DARPA), in essence creating a network of networks, was done by Vinton Cerf and Robert Kahn [Cerf 1974]; the term internetting was coined to explain this work.

These architectural principles were represented in TCP. The early versions of TCP, though, were quite different from today's TCP, The early versions of TCP combined a dependable in-sequence delivery of data via end-system retransmission (still part of today's TCP) with forwarding functions (which today are performed by IP). Early experimentation with TCP, combined with the recognition of the importance of an unreliable, non-flow-controlled, end-to-end transport service for applications such as packetized voice, led to the separation of IP out of TCP and the development of the UDP protocol. The three key Internet protocols that we see today - TCP, UDP, and IP - were conceptually in place by the end of the 1970s.

In addition to the DARPA Internet-related research, many other important networking activities were in progress. In Hawaii, Norman Abramson was developing ALOHAnet, a packet-based radio network that allowed numerous remote sites on the Hawaiian Islands to communicate with each other. The ALOHA protocol [Abramson 1970] was the first multiple-access protocol, allowing geographically distributed users to share a single broadcast communication medium (a radio frequency). Metcalfe and Boggs built on Abramson's multiple-access protocol work when they developed the Ethernet protocol [Metcalfe 1976] for wire-based shared broadcast networks; see the following figure. Interestingly, Metcalfe and Boggs Ethernet protocol was motivated by the need to connect multiple PCs, printers, and shared disks [Perkins 1994]. Twenty-five years ago, well before the PC revolution and the explosion of networks, Metcalfe and Boggs were laying the foundation for today's PC LANs. Ethernet technology represented an important step for internetworking as well. Each Ethernet local area network was itself a network, and as the number of LANs increased rapidly, the need to internetwork these LANs together became progressively more important. We'll discuss Ethernet, ALOHA, and other LAN technologies in detail in "The Link Layer and Local Area Networks".

Metcalfes original conception of the Ethernet



Tags

packet switching, network, protocol

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