Comunications A.
THEORY



  1. History of the Internet
    1962 - 1969
    The Internet is first conceived in the early '60s. Under the leadership of the Department of Defense's Advanced Research Project Agency (ARPA), it grows from a paper architecture into a small network (ARPANET) intended to promote the sharing of super-computers amongst researchers in the United States.
    1. The RAND Corporation begins research into robust, distributed communication networks for military command and control.
    2. 'Dr Strangelove' portrays nuclear holocaust which new network must survive
    3. The DOD's Advanced Research Project Association begins work on 'ARPANET'
    4. ARPA sponsors research into a "cooperative network of time-sharing computers."
    5. First ARPANET papers presented at Association for Computing Machinery Symposium
    6. Delegates at a symposium for the Association for Computing Machinery in Gatlingberg, discuss the first plans for the ARPANET.
    7. ARPANET connects first 4 universities in the United States. Researchers at four US campuses create the first hosts of the ARPANET, connecting Stanford Research Institute, UCLA, UC Santa Barbara, and the University of Utah.
    1970 - 1973
    The ARPANET is a success from the very beginning. Although originally designed to allow scientists to share data and access remote computers, email quickly becomes the most popular application. The ARPANET becomes a high-speed digital post office as people use it to collaborate on research projects and discuss topics of various interests.
    1. ALOHANET developed at the University of Hawaii
    2. The ARPANET grows to 23 hosts connecting universities and government research centers around the country.
    3. The InterNetworking Working Group becomes the first of several standards-setting entities to govern the growing network. Vinton Cerf is elected the first chairman of the INWG, and later becomes known as a "Father of the Internet."
    4. The ARPANET goes international with connections to University College in London, England and the Royal Radar Establishment in Norway.
    1974 - 1981
    The general public gets its first vague hint of how networked computers can be used in daily life as the commercial version of the ARPANET goes online. The ARPANET starts to move away from its military/research roots.
    1. Bolt, Beranek & Newman opens Telenet, the first commercial version of the ARPANET.
    2. Internet operations transferred to the Defense Communications Agency
    3. Queen Elizabeth goes online with the first royal email message.
    4. UUCP provides email on THEORYNET
    5. TCP checksum design finalized
    6. Tom Truscott and Jim Ellis, two grad students at Duke University, and Steve Bellovin at the University of North Carolina establish the first USENET newsgroups. Users from all over the world join these discussion groups to talk about the net, politics, religion and thousands of other subjects.
    7. ARPANET has 213 hosts. A new host is added approximately once every 20 days.
      1982 - 1987
      Bob Kahn and Vint Cerf are key members of a team which creates TCP/IP, the common language of all Internet computers. For the first time the loose collection of networks which made up the ARPANET is seen as an "internet", and the Internet as we know it today is born.

      The mid-80s marks a boom in the personal computer and super-minicomputer industries. The combination of inexpensive desktop machines and powerful, network-ready servers allows many companies to join the Internet for the first time. Corporations begin to use the Internet to communicate with each other and with their customers.

      1. The term 'Internet' is used for the first time.
      2. TCP/IP becomes the universal language of the Internet
      3. William Gibson coins the term "cyberspace" in his novel "Neuromancer." The number of Internet hosts exceeds 1,000.
      4. Internet e-mail and newsgroups now part of life at many universities
      5. Case Western Reserve University in Cleveland, Ohio creates the first "Freenet" for the Society for Public Access Computing.
      6. The number of Internet hosts exceeds 10,000.
      1988 - 1990
      By 1988 the Internet is an essential tool for communications, however it also begins to create concerns about privacy and security in the digital world. New words, such as "hacker," "cracker" and" electronic break-in", are created.

      These new worries are dramatically demonstrated on Nov. 1, 1988 when a malicious program called the "Internet Worm" temporarily disables approximately 6,000 of the 60,000 Internet hosts.

      1. Internet worm unleashed
      2. The Computer Emergency Response Team (CERT) is formed to address security concerns raised by the Worm.
      3. System administrator turned author, Clifford Stoll, catches a group of Cyberspies, and writes the best-seller "The Cuckoo's Egg." The number of Internet hosts exceeds 100,000.
      4. A happy victim of its own unplanned, unexpected success, the ARPANET is decommissioned, leaving only the vast network-of-networks called the Internet. The number of hosts exceeds 300,000.
      1991 - 1993
      Corporations wishing to use the Internet face a serious problem: commercial network traffic is banned from the National Science Foundation's NSFNET, the backbone of the Internet. In 1991 the NSF lifts the restriction on commercial use, clearing the way for the age of electronic commerce.

      At the University of Minnesota, a team led by computer programmer Mark MaCahill releases "gopher," the first point-and-click way of navigating the files of the Internet in 1991. Originally designed to ease campus communications, gopher is freely distributed on the Internet. MaCahill calls it "the first Internet application my mom can use." 1991 is also the year in which Tim Berners-Lee, working at CERN in Switzerland, posts the first computer code of the World Wide Web in a relatively innocuous newsgroup, "alt.hypertext." The ability to combine words, pictures, and sounds on Web pages excites many computer programmers who see the potential for publishing information on the Internet in a way that can be as easy as using a word processor.

      Marc Andreesen and a group of student programmers at NCSA (the National Center for Supercomputing Applications located on the campus of University of Illinois at Urbana Champaign) will eventually develop a graphical browser for the World Wide Web called Mosaic.

      1. The World Wide Web is born!
      2. Traffic on the NSF backbone network exceeds 1 trillion bytes per month.
      3. One million hosts have multi-media access to the Internet over the MBONE

      4. The first audio and video broadcasts take place over a portion of the Internet known as the "MBONE." More than 1,000,000 hosts are part of the Internet.
      5. Mosaic, the first graphics-based Web browser, becomes available. Traffic on the Internet expands at a 341,634% annual growth rate.
      1994
      The Rolling Stones broadcast the Voodoo Lounge tour over the M-Bone. Marc Andreesen and Jim Clark form Netscape Communications Corp. Pizza Hut accepts orders for a mushroom, pepperoni with extra cheese over the net, and Japan's Prime Minister goes online at www.kantei.go.jp. Backbone traffic exceeds 10 trillion bytes per month.
      1995
      NSFNET reverts back to a research project, leaving the Internet in commercial hands. The Web now comprises the bulk of Internet traffic. The Vatican launches www.vatican.va. James Gosling and a team of programmers at Sun Microsystems release an Internet programming language called Java, which radically alters the way applications and information can be retrieved, displayed, and used over the Internet.
      1996
      Nearly 10 million hosts online. The Internet covers the globe

      As the Internet celebrates its 25th anniversary, the military strategies that influenced its birth become historical footnotes. Approximately 40 million people are connected to the Internet. More than $1 billion per year changes hands at Internet shopping malls, and Internet related companies like Netscape are the darlings of high-tech investors.

      Users in almost 150 countries around the world are now connected to the Internet. The number of computer hosts approaches 10 million.

      Within 30 years, the Internet has grown from a Cold War concept for controlling the tattered remains of a post-nuclear society to the Information Superhighway. Just as the railroads of the 19th century enabled the Machine Age, and revolutionized the society of the time, the Internet takes us into the Information Age, and profoundly affects the world in which we live.

      The Age of the Internet has arrived.

      1997
      Today some people telecommute over the Internet, allowing them to choose where to live based on quality of life, not proximity to work. Many cities view the Internet as a solution to their clogged highways and fouled air. Schools use the Internet as a vast electronic library, with untold possibilities. Doctors use the Internet to consult with colleagues half a world away. And even as the Internet offers a single Global Village, it threatens to create a 2nd class citizenship among those without access. As a new generation grows up as accustomed to communicating through a keyboard as in person, life on the Internet will become an increasingly important part of life on Earth.


  2. OSI Reference Model
    In an effort to standardize telecommunication the OSI (Open Systems Interconnect) model was developed. The seven layer model has the physical connection the lower layer and applications protocols at the upper layers. This model is widely accepted as a basis for the understanding of how a network protocol stack should operate. It also serves as a reference for comparing network stack implemenations.

    Application

    Network applications such as terminal emulation and file transfer.

    Presentation

    Formatting of data and encryption

    Session

    Establishment and maintenance of sessions

    Transport

    Provision of reliable and unreliable end-to-end delivery

    Network

    Packet delivery, including routing

    Data Link

    Framing of units of information and error checking

    Physical

    Transmission of bits on the physical hardware



  3. TCP/IP protocol Stack.
    The TCP/IP protocol suite is named for two of its most important protocols: Transmission Control Protocol (TCP and Internet Protocol (IP). Another name is the Internet Protocol Suite.


    Applications

    SMTP, Telenet, FTP, Gopher, HTTP ...


    Transport

    		TCP / UDP
    InternetworkIP ICMP
    ARP/RARP


    Network Interface
    and
    Hardware

    Ethernet, TokenRing, FDI, X.25, Wirless, Async, ATM, SNA...


    1. Application Layer
      An application is a user process cooperating with another proccess on the same level on the same or different hosts. The interface bewteen the application and the transport layers is defined by port numbers and sockets. Examples of applications are: telnet, FTP, SMTP, HTTP and gopher.

    2. Transport Layer
      The transport layer provides end-to-end data transfer. Multiple applications can be supported simultaneously. The transport layer is responsible for reliable exchange of information. The main protocols in this layer are TCP, Transmission Control Protocol and UDP, User datagram Protocol.TCP is a connection-oriented service, while UDP is a connectionless service.

    3. Internetwork Layer
      Also called the internet layer or the network Layer provides the "virtual network" image of an internet (This layer shields the higher levels from the physical network architecture below it).
      Internet Protocol IP is the most important protocol in this layer. It is a connectionless protocol that doesn't asume reliabilityi from the lower layers. IP does not provide reliability, flow control or error recovery. These functions must be provided at a higher level.

      Part of communicationg messages bewteen computers is a routing function that ensures that messages will be correctly delivered to their destination. IP provides this rotuing function. A message unit in an IP network is called an IP datagram. Other internetwork protocols are: icmp - internet control message protocol, arp - address resolution protocol, and rarp - reverse address resolution protocol.

    4. Network Interface Layer
      Also called the Link layer or the data-link layer is the interfcae to the actual network hardware. This interface may or may ot provide reliable delivery and may be packet or stream oriented. TCP/IP does not specify any protocol, but can use almost any interface. Examples of interfaces ae: IEEE 802.2, X.25, ATM, FDI, and SNA


  4. Physical Layer.
    1. Ethernet.
      The most popular type of local area network, which sends its communications through radio frequency signals carried by a coaxial cable.Each computer checks to see if another computer is transmitting and waits its turn to transmit.If two computers accidentally transmit at the same time and their messages collide, they wait and send again in turn.
    2. Token Ring.
      A local area network in which computers are configured in a ring, and a message called a token is passed from station to station.The token is used to avoid conflicts in transmission; a machine can only transmit messages while it holds the token.The most common type of token ring is defined in the IEEE 802.5 standard.
    3. FDDI Fiber Distributed Data Interface.
      Fiber Distributed Data Interface.An ANSI standard for 100 Mbit/s data transmission through fiber optic cable, in a token ring setup.Many local area networks can be linked together with a backbone that uses FDDI.
    4. ATM Asynchronous Tranfer Mode.
      (ATM).A type of fast packet switching that uses a fixed size packet called a cell.This technique makes it possible to transmit data at great speed, and can make voice, multimedia, full-motion video, and video conferencing available to all users.It also makes dynamic allocation of bandwidth possible; telephone and cable TV companies can charge individual customers based on the amount of bandwidth they use.
    5. SLIP Serial Line IP
      Serial Line Internet Protocol.Software which uses the Internet Protocol (TCP/IP) over a serial line.SLIP makes it possible for a computer to communicate with other computers by means of a dial-up connection; for example, a serial port hooked to a modem that makes a connection between two local area networks or is used to access the Internet and World Wide Web.
    6. PPP Point-to-Point.
      Point to Point Protocol.A protocol for communication between computers using TCP/IP, over standard telephone lines, ISDN, and other high-speed connections.PPP was developed by the Internet Engineering Task Force (IETF) and is defined in RFC 1171.It can be used to connect a computer to the Internet, for services such as the World Wide Web and email.PPP is faster than SLIP and has better error correction; it can be used with both synchronous and asynchronous transmission.
    7. ISDN Integrated Services Digital Network.
      Integrated Services Digital Network.Digital telecommunications lines that can transmit both voice and digital network services up to 128K, and are much faster and more reliable than high-speed analog modems.ISDN lines are offered by many telephone companies.
    8. X.25
      An ITU-T standard protocol suite for the DTE-DCE interface in a packet-switched network, approved by ISO. X.25 defines standard physical layer, data link layer and network layers (layers 1 through 3). It was developed to describe how data passes into and out of public data communications networks. X.25 networks are in use throughout the world.
    9. Frame Relay.
      A protocol for sending small packets of data over a network.Frame relay uses packets of variable length, unlike cell relay, and requires less stringent error detection than other forms of packet switching because it is designed to take advantage of the more reliable circuits that have become available in recent years.Frame relay is often used for wide area networks, where it can transmit data at high speed more efficiently than point-to-point services.Frame relay is used with digital lines.


  5. Application Protocols.
    1. DNS - Domain Name System

      The Internet's standard for host names and a hierarchical system of domain name servers to resolve them into IP addresses (such as 199.12.1.1).

      Replaces the hosts.txt file on individual machines that used to perform this function (and becomes difficult to administer when there are more than a few stations on a network).

      Each name server has the IP address of a name server higher in the hierarchy to which it sends queries that it cannot resolve itself.

      A full DNS name (for example) is zucchini.austin.cc.tx.us. zucchini is the name of our host in the subdomain, austin.cc.tx is the name of our network, all in the United States "top-level domain."

      Some top-level domain names are listed in the following table.

      Domain Name User
      arpaARPAnet
      comCommercial organizations
      eduEducational institutions
      govGovernment organizations
      milU.S.-based military
      netInternet access providers
      orgNonprofit organizations

      A recent change is top-level domain names are now often geographically related. ISO 3166 specifies the two-letter country codes to be used.

      DNS is distributed in that name servers keep track of hosts that are below them in the hierarchy. Usually, each site has a name server for its local machines. The most popular implementation of DNS is the Berkeley Internet Name Daemon (bind), it is usually just another process on a UNIX host.

      End-user stations have a name resolver that caches frequent DNS queries. Their name resolver configuration file has IP addresses of a few nearby name servers.

      The process for registering for a (guaranteed worldwide unique and known) domain name (and IP address) involves filling out a form. Usually, your Internet service provider will do this for you, but you can do it yourself as well (though you need to know the address of your name server). Where the form comes from (and to whom you return it) depends on the type of name desired.

      • Names in the (for example) .com and .net top-level domains are administered by the InterNIC.

      • Names in the .ca top-level domain are administered by the CA domain registrar.

      Determining the registered DNS name for an organization can be done by telnetting to the InterNIC (to rs.internic.net and running the whois command or to ds.internic.net and select the White Pages menu item) or, using WWW, use URL http://www.csi.nb.ca/domain (for the .ca domain).

    2. telnet - Terminal Emulation

      Terminal emulation with communications to the host over a network (rather than through an EIA-232 connection).

      The telnet protocol provides a standadized interface, through which a program on one host (The telnet client) can access the resources of another host (the telnet server) as though the client were a local terminal connected to the server.

      That is, typing telnet servername connects you to the host servername. Your session then continues as if your terminal (likely actually a PC running a data communications program that makes your PC emulate a terminal) was directly connected to the remote host. You are prompted for a username and a password.

    3. ftp - File Transfer Protocol

      File Transfer Protocol.A client/server protocol for exchanging files with a host computer.

    4. tftp - Trivial File transfer Protocol

      A simple file transfer protocol (a simplified version of ftp) that is often used to boot diskless workstations and other network devices (such as routers) over a network (typically a LAN).

      Has no password security.

    5. rsh

      Remote shell protocol. Allows ruuning commands on a remote host.

    6. smtp

      The protocol used in TCP/IP networks for transferring electronic mail messages between end user computers and mail servers. Popular freeware SMTP mail programs for user workstations are Elm and Pine. Since mail messages cannot have control characters in them, binary files must first be converted into ASCII often using uuencode (usually a separate program; the corresponding program at the other end is then uudecode, which converts the file back to binary) or MIME. SMTP is used only when both the mail sender and receiver are ready at the same time. If (for example) the destination PC is not connected (it dials in periodically to an ISP), then a post office must be used to temporarily store the mail. A post office protocol (such as IMAP or POP) must then be used to retrieve the mail.

    7. pop

      The older type of Internet mail server. Most new servers are IMAP. POP downloads all mail to a user as soon as the user connect to the mail server.

    8. imap4

      The newer type of Internet mail server. It allows connected stations to first view message headers and choose which, of the mail messages for them, they wish to receive. (The others remain stored on the mail server.) Can work with the older POP2 and POP3 mail servers, only offering the POP functionality (for example, you need to accept all mail messages once a connection is established to the mail server).

    9. lpd

      Line printer Daemon. Allows printing to printers connected via the network.

    10. nfs

      A method of mapping (technically called "mounting") shared remote disk drives so that they appear to be local. Developed and licensed by Sun Microsystems. Uses UDP, not TCP. Defined in RFC 1094.

    11. http

      The protocol used to carry WWW traffic between a WWW browser computer and the WWW server being accessed. The protocol is documented at http://www.w3.org.

    12. nntp

      Network News Transfer Protocol.Internet protocol for connecting to Usenet newsgroups and post messages.

    13. gopher

      A method of snooping through the Internet for files and retrieving them. Easier to use than the ftp utility (though gopher actually retrieves files using ftp), but not nearly as much fun, and not as powerful as the WWW. A series of menus (on destination machines) provide pointers to resources, which the gopher client software (running on your local machine) displays, or uses as a trigger to launch other applications, such as telnet or WAIS. Many WWW browsers can also be gopher clients (for example, enter gopher://internic.net/ into Netscape). The name comes from the system's function: to "go fer" things. Also, it was developed at the University of Minnesota, and its Twin Cities campus athletic teams are called the Gophers. The gopher FAQ is at ftp://rtfm.mit.edu/pub/usenet/news.answers/gopher-faq.

    14. snmp

      Defined in RFC 1!57, snmp executes network management applications that monitor and control the network.

    15. BOOTP

      The BOOTstrap protocol enables a client workstation to initialize with a minimal IP stack. This is useful for diskless clients.

© Allan Kochis Last revision 4/11/2001