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Intro. to Computer Networks

Intro. to Computer Networks. Some Terminology Computer network an interconnected collection of autonomous computers Distributed system a software system built on top of a network Client-server model Use of Computer Network Networks for companies

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Intro. to Computer Networks

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  1. Intro. to Computer Networks Some Terminology • Computer network an interconnected collection of autonomous computers • Distributed system a software system built on top of a network • Client-server model Use of Computer Network • Networks for companies resource sharing, flexibility& reliability, information exchange • Networks for people access to remote info/processing, person-to-person comm., interactive entertainment • Social issues politics, religion, sex, employee vs. employer rights, anonymous msg. C S

  2. Classification of Networks Based on transmission technology • Broadcast networks single comm. Channel shared by all machines on the network address field in the packets/messages required to identify the destination • Point-to-point networks consisting of many connections btw individual pairs of computers S  (R  …  R)  D routing algorithms play an important role in this type of networks Based on scale • LANs  building, campus • MANs  city • WANs  country, continent • the Internet  planet the current special one we are using everyday A General rule • Smaller, geographically localized networks tend to use broadcasting • Larger networks: usually P-to-P

  3. Example Networks ARPANET • Introduced around 1970 by ARPA of DoD IMP: Interface Message Processor • Original ARPANET design • Software split into two parts subnet software (by BBN) host software (by then graduate students) • Subnet 1st electronic store-and-forward packet-switching network (56 Kbps) S_IMP- D_IMP protocol H-H protocol H H-IMP protocol Subnet IMP-IMP protocol

  4. To handle communication over internetworks TCP/IP model and protocol developed and integrated into the Berkeley UNIX system (Unix 4.2 BSD + TCP/IP + Sockets + Network utilities) • Split in 1983 into a military subnet (MILNET) and a research subnet • DNS created in 1980s to organize machines into domain and map host names onto IP addresses • By 1990 ARPANAT has been overtaken by newer networks, so it was shut down and dismantled. MILNET continues to operate

  5. NSFNET • Late 1970s CSNET (a virtual network) was set up to support dial-up lines & connections to ARPANET • 1980s A backbone network built to connect NSF’s six supercomputer centers (S.D., Boulder, Champaign, Pittsburgh, Ithaca, Princeton) Some regional networks funded by NSF to allow users for accessing supercomputers and for communicating one another (the backbone + the regional networks  NSFNET) • 1990s NREN (the research successor to NSFNET running at Gbps speeds

  6. The Internet An internet: a collection of interconnected networks The Internet: a specific worldwide internet • Growth of the Internet by 1990: about 200K hosts by 1992: > 1 M host by 1995: multiple backbones hundreds of regional networks tens of thousands of LANs millions of hosts tens of millions of users the size doubles approximately every year by now: difficult to count • Traditionally, 4 main applications: Email, News, Remote login, File transfer mainly used by academic, government, & industrial reserachers • Killer application: WWW The application that brought tens of millions of new, non-academic users to the net

  7. Who’s Who In the Telecomm. World: • Common Carriers companies that provide comm. Services to the public • ITU (Int’l Telecomm. Union), formally known as CCITT (1956-1993) * an agency of the United Nations * responsible for standardizing int’l telecommunications * 3 main sectors: ITU-R (Radiocomm.), ITU-D (Development) ITU-T (Telecomm. Standardization) In the Int’l Standards World: • ISO (Int’l Standards Organization) a voluntary non-treaty org. formed by national standards org. of 89 member countries • ANSI (American Nat’l Standards Institute) * the U.S. representative in ISO * a private, nongovernmental, non-profit org. * ANSI standards often  ISO standards • NIST (Nat’l Institute of Standards and Technology)

  8. Who’s Who (Cont’d) In the Internet World: • IAB (Internet Architecture Board) IAB  DoD and NSF (RFC) • IAB  IRTF and IETF in 1989 IRTF: Internet Research Task Force concentrates on long-term research IETF: Internet Engineering Task Force deals with short-term engineering issues • Standardization Process RFC  Proposed Standard  Draft Standard  Internet Standard RFC  Proposed Standard: idea completely explained and sufficient interest in the community Proposed Standard  Draft Standard: working implementation + tested by two indep. Sites for 4 months Draft Standard  Internet Standard: IAB convinced that the idea is sound and the software works

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