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A Packet Switched Network, or PSN, refers to the packet switched networks that existed before Internet. History can be divided into three eras: Early networks before the introduction of X.25 and OSI X.25 era when many PTTs introduced networks with X.25 interfaces Internet era when restrictions on connection to the Internet were removed. Early Networks ARPANET and SITA HLN became operational in 1969. Before the introduction of X.25 in 1969, about twenty different network technologies were developed. There was a debate about the merits of two drastically different views as to proper division of labour between the hosts and the network. In the datagram system the host must detect loss or duplication of packets. Transmission Control Protocol /Internet Protocol (TCP/IP) is the best known example of a host to datagram protocol. In the virtual call system, the network guarantees sequenced delivery of data to the host. This results in a simpler host interface with less functionality than in the datagram model. X.25 is the best known virtual call protocol. Inexpensive minicomputers were an important component in the early networks. In some cases custom I/O devices were added to allow inexpensive or exotic attachments to communication lines. Arpanet This is the principal survivor from the early era. TCP/IP which was an important component of ARPANET2 was chosen for use in NSFNET which eventually became the Internet. BNRNET BNRNET was a network which Bell Northern Research developed for internal use. It initially had only one host but was designed to support many hosts. BNR later made major contributions to the CCITT X.25 project. CTNE Compañía Telefónica Nacional de España was the national telephone company in Spain. They developed a network called RETD. See below for details. CYCLADES CYCLADES was an experimental French network. Louis Pouzin was the principal designer. Some ideas from this network were later incorporated into ARPANET. DDX-1 This was an experimental network from Nippon PTT. It mixed circuit switching and packet switching. It was succeeded by DDX-2. EIN nee COST II European Informatics Network was a project to link several national networks. It became operational in 1976. EPSS EPSS (Experimental Packet Switching System) was an experiment of the UK Post Office. Ferranti supplied the hardware and software. The handling of link control messages (acknowledgements and flow control) was differed from that of most another networks and is not fully explained in the published literature. GE IS General Electric was the major international provider of information services. They designed a network to connect their worldwide customers to a large data center near Cleveland, Ohio. Very little has been published about the internal details of their network. The design was hierarchal with redundant communication links. Two papers provides some details. IPSANET IPSANET was a semi-private network constructed by I. P. Sharp Associates to serve their time-sharing customers. It became operational in May 1976. NPL Donald Davies of the National Physical Laboratory, UK made many important contributions to the theory of packet switching. NPL built a single node network to connect sundry hosts at NPL. OCTOPUS Octopus was a local network at Lawrence Livermore National Laboratory. It connected sundry hosts at the lab to interactive terminals and various computer peripherals including a bulk storage system. Philips Research Philips Research Laboratories in Redhill, Surrey developed a packet switching network for internal use. It was a datagram network with a single switching node. RCP RCP was an experimental network created by the French PTT. It was used to gain experience with packet switching technology before the specification of TRANSPAC was frozen. RCP was a virtual-call network in contrast to CYCLADES which was based on datagrams. RCP emphasised terminal to host and terminal to terminal connection; CYCLADES was concerned with host-to-host communication. TRANSPAC was introduced as an X.25 network. RCP may have influenced the specification of X.25. RETD Red Especial de Transmisión de Datos was a network developed in Spain. It became operational in 1972 and thus was the first public network. SCANNET "The first experimental packet-switched Nordic telecommunication network SCANNET was implemented in Nordic technical libraries in 70's, and it included first Nordic electronic journal Extemplo. Libraries were also among first ones in universities to accommodate microcomputers for public use in early 80's." The preceding paragraph taken from: * SITA HLN SITA is a consortium of airlines. Their High Level Network became operational in 1969 at about the same time as ARPANET. It carried interactive traffic and message-switching traffic. As with many non-academic networks very little has been published about it. SNA Systems Network Architecture (SNA) is IBM's proprietary networking architecture created in 1974. An IBM customer could acquire hardware and software from IBM and lease private lines from a common carrier. This allowed construction of a private network. Telenet Telenet was the first FCC-licensed public data network in the United States. It initially used ARPANET technology. Tymnet Tymnet was an international data communications network headquartered in San Jose, CA that utilized virtual call packet switched technology and used X.25, SNA/SDLC, BSC and ASCII interfaces to connect host computers (servers)at thousands of large companies, educational institutions, and government agencies. Users typically connected via dial-up connections or dedicated async connections. The business consisted of a large public network that supported dial-up users and a private network business that allowed government agencies and large companies (mostly banks and airlines) to build their own dedicated networks. The private networks were often connected via gateways to the public network to reach locations not on the private network. Tymnet was also connected to dozens of other public networks in the U.S. and internationally via X.25/X.75 gateways. X.25 Era There were two kinds of X.25 networks. Some such as DATAPAC and TRANSPAC were initially implemented with an X.25 external interface. Some older networks such as TELENET and TYMNET were modified to provide a X.25 host interface in addition to older host connection schemes. DATAPAC was developed by Bell Northern Research which was a joint venture of Bell Canada (a common carrier) and Northern Telecom (a telecommunications equipment supplier). Northern Telecom sold several DATAPAC clones to foreign PTTs including the Deutsche Bundespost. X.75 and X.121 allowed the interconnection of national X.25 networks. A user or host could call a host on a foreign network by including the DNIC of the remote network as part of the destination address. Austpac AUSTPAC is an Australian public X.25 network operated by Telstra. Started by the then-Telecom in the early 1980s, AUSTPAC was Australia's first public packet-switched data network, supporting applications such as on-line betting, financial applications — the Australian Tax Office has made use of AUSTPAC — and remote terminal access to academic institutions, who maintained their connections to AUSTPAC up until the mid-late 1990s in some cases. Access can be via a dial-up terminal to a PAD, or, by linking a permanent X.25 node to the network. ConnNet ConnNet was a packet switched data network operated by the Southern New England Telephone Company serving the state of Connecticut. Datapac DATAPAC was the first operational X.25 network (1976). It covered major Canadian cities and was eventually extended to smaller centres. Datex-P Deutsche Bundespost operated this national network in Germany. The technology was acquired from Northern Telecom. RCA RCA Transpac Transpac was the national X.25 network in France. It was developed locally at about the same time as DataPac in Canada. The development was done by the French PTT and influenced by the experimental RCP network. It began operation in 1978. Internet Era When Internet connection was made available to anyone who could pay for an ISP subscription, the distinctions between national networks blurred. The user no longer saw network identifiers such as the DNIC. Some older technologies such as circuit switching have resurfaced with new names such as fast packet switching. Researchers have created some experimental networks which to complement the existing Internet. Internet2 Internet2 is not an actual network. It is a research consortium which has created the Abilene Network. National LambdaRail National LambdaRail is a high-speed national computer network in the United States that runs over fiber-optic lines, and is the first transcontinental Ethernet network. TransPAC2 See also | |||||||
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