Computer Networks and the Internet

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Computer Networksand the Internet

• CMPT 109
• Montclair State University

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Computer Data Communication

• Computer Data communications involves
  transmitting information on the form of coded bit
  patterns over appropriate channels.
• Download The action of retrieving data into your
  computer.
• Upload The action of sending data into another
  computer (you need privileges to access the other
  computer).

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Data Communication

• Data Communication can be established using
  analog or digital signal.
• Analog signal is a continuous wave pattern. The
  telephone system uses analog signals
• Digital signal consists of a series of 1s and 0s.
  HDTV uses digital signals.
• Signal can be of any kind Electric current,
  electromagnetic waves, light pulses, etc.

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Telephone Network Circuit Switching

• When you make a telephone call

• The telephone switching system creates an
  electrical circuit between two telephones

• The switching system maintains this circuit until
  you hang up.

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Circuit Switching (continued)

• Appropriate for telephone networks
• Analog data is degraded at each station
• Telephone conversations require relatively
  continuous flow of data across circuit
• Not appropriate for computer networks
• Digital data does not degrade at links, so more
  intermediate nodes are possible.
• Computers generate data in bursts, with long
  intervening periods of silence, wasting
  bandwidth

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Computer Networks

• It normally consists of tow or more independent
  computer connected together with communication
  links and equipment, to share resources
• There are two types of networks WAN (Wide Area
  Network) and LAN (Local Area Network).
• WANs may span great geographic distances.
• LANs connect computers located not far away.

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Computer Networks

• WANs share software and information
• LANs share devices, software and information
• The communication links are full-duplex, i.e both
  computers can communicate simultaneously. A
  half-duplex communication only allows one
  computer to transmit at any given time.

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Computer Networks Packet Switching

• Connect computers in a network, often with
  redundant links. Each computer is a node in the
  network.
• Source computer splits message into one or more
  packets, each with part of message.
• Each packet also contains address of destination
  computer.
• Source computer sends packets to an adjacent node
  in the network.

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Packet Switching (continued)

• When a networked computer receives a packet, it
  examines the packets address.
• If the computer is not the packets final
  destination, it forwards the packet to an
  adjacent node thats closer to the packets
  destination.
• The destination computer collects the packets and
  re-assembles them into the original message.

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Packet Switching Illustration
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HELP (to 8)
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Some Remarks about Packet Switching

• Not all the packets in a message need to take the
  same route between source and destination.
• The packets in the message do not need to arrive
  at the destination in proper order.
• Messages transmitted via a packet-switched
  network are inherently vulnerable to unauthorized
  interception.

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Network Protocols

• A protocol is a set of rules for exchange of data
  among two or more parties (e.g., among computers
  in a network).
• A packet-switched network protocol needs to
  specify the following (at a minimum)
• The structure of a packet
• Format for source and destination address
• Routing of packets through the network
• Splitting and reassembling of messages

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Types of Protocols

• A general communication protocol often contains
  specific protocols for different types of
  messages.
• For example, there may be protocols for
• Remote logins
• Transfer (actually copying) of data files
• E-mail messages

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WANs

• They need hardware to connect the computers. It
  could be a modem and the POTS, or a modem and a
  ADSL connection.
• They also need software to synchronize the
  transmission of the data between the two
  computers.

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LANs

• They need hardware to connect the computers A
  NIC (Network Interface Card), and some type of
  cabling (twisted pair, coaxial, fiber optic).
• They also need the software, that must
  correspond to the network topology that is being
  used.

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Network Topologies

• A topology is the physical arrangement of the
  computers in a network
• In a star topology, each computer is linked to a
  central computer.
• In a ring topology, the computers are arranged in
  a circle.
• In a bus topology, computers (or sub-networks)
  are linked to a backbone.
• In a mesh topology, computers a linked in a
  (rectangular) grid.

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A Star Topology
Client
Client
Client
Server
Client
Client
Client
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A Ring Topology
Node
Node
Node
Messages are passed in this direction
Node
Node
Node
Node
Node
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A Bus Topology
Node
Node
Node
Node
Node
Node
Server
Node
Node
Backbone
Node
Node
Node
Node
Server
Node
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Mesh Topology
Node
Node
Node
Node
Node
Node
Node
Node
Node
Node
Node
Node
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MSUs Local Area Network

• Essentially a bus topology, with several
  sub-networks. Machines communicate using the
  Ethernet protocol.
• The PCs in RI 105 and RI 108 -- together with the
  server in RI 109 -- form one sub-network. The
  PCs are clients.
• Most of the other PCs on campus are parts of
  different sub-networks

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The Internet

• The Internet is really a network of networks,
  with no specified topology.
• The LAN at MSU is one of the networks in the
  Internet.
• The protocol for communication over the Internet
  is TCP/IP (Transmission Control Protocol/Internet
  Protocol).

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Internet Protocols

• telnet -- allows remote logins
• ftp -- file transfer protocol
• mailto -- protocol for sending e-mail
• http -- hypertext transfer protocol. This
  protocol makes the World Wide Web possible.

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The World Wide Web

• The part of the Internet that uses hypertext.
• Web pages written in hypertext markup language
  (HTML) may contain embedded hypertext links to
  other pages. This other page may be anywhere on
  the Internet.
• A hypertext link to a page makes use of that
  pages Uniform Resource Locator (URL).

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WWW (continued)

• A web browser is a program that allows one to
  view documents written in HTML and to traverse
  the embedded hypertext links.
• The two major web browsers are Netscape Navigator
  and Microsofts Internet Explorer. Other
  browsers exist (e.g. Lynx).
• Hypertext links allow one to access information
  without having to know its physical location.
• Instead, the URL for the physical location is
  embedded in the HTML document.