Ch1 - Wenli Wangs homepage

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					      Chapter 1

Introduction to Computer
   Networks and Data
        Learning Objectives
• Define the basic terminology of computer networks
• Recognize the individual components of the big picture
  of computer networks
• Outline the basic network configurations
• Cite the reasons for using a network model and how
  those reasons apply to current network systems
• List the layers of the OSI model and describe the
  duties of each layer
• List the layers of the Internet model and describe the
  duties of each layer
• Compare the OSI and Internet models and list their
  differences and similarities

The transmission of a signal by way of a medium
             from sender to receiver

       Sender      Signal      Receiver

Communication Problems

   Completeness & comprehension
   Attenuation & noises
   Competing resources
   Routing & addressing
   Security
   Computer network
   Voice network
   Data network
   Local area network (LAN)
   Metropolitan area network (MAN)
   Wide area network (WAN)
   Personal area network
   Etc.
   Datacom:
      The movement of computer information (data)

       from one point to another by means of electrical
       or optical transmission systems
      Is a sub-field of telecommunications

   Telecom:
      Includes the transmission of voice and video as

       well as data
   Trend:
      digital convergence of datacom and telecom
      Network Configurations
   Terminal/PC-to-mainframe
   PC-to-LAN
   PC-to-Internet
   Personal area network-to-workstation (PC)
   LAN-to-MAN
   LAN-to-WAN
   WAN-to-WAN
   Sensor-to-LAN
   Satellite and microwave
   Wireless telephone
         Network Architectures
   OSI (Open Systems Interconnection) Model

       ISO (International Organization for Standardization)
       ITU-T (International Telecommunications Union-
        Telecommunications Standards Sector)
       Work Together because Networking Involves both
        Computers and communications

   Internet TCP/IP protocol suite (or stack)
      Originally under DARPA (Defense Advanced Research
       Projects Agency)
      Now under an independent body, the IETF (Internet
       Engineering Task Force)

   Layered Approach, Why? (later)
   Standards are rules of operation that are followed by
    most or all vendors.

   Standards allow products from different vendors to
    work together (interoperate)
          not limited to buy from one firm.
          Competition will drive down costs and increase options
          do not have to worry if a single vendor falls behind or
The OSI Model

      Logical vs. Physical

Application         Application

Presentation       Presentation

  Session            Session

 Transport          Transport

 Network             Network

  Datalink           Datalink

  Physical           Physical
           Internet Standards
   The IETF Does Not Create Single Network Standards
      Uses standards from another architecture, OSI

      Reference Model of Open Systems Interconnection


                              Single Network:
                             Use OSI Standards
           Internet Standards
   OSI Divides Subnet Standards into Two Layers
     Data Link

     Physical


                        Single Network   Data Link
                           Standards     Physical
OSI vs. The Internet



  Transport     Transport

   Network       Network

   Datalink      Network
   Physical       Access
 OSI vs. Internet

     OSI           TCP/IP Suite
Application (7)
Presentation (6)   Application
  Session (5)
 Transport (4)      Transport

 Network (3)         Internet
 Data Link (2)     Data Link (2)
 Physical (1)      Physical (1)
        Internet Standards &
   Application Layer
       allow two applications to work together, even if they
        come from different vendors
       HTTP, SMTP, POP, IMAP, FTP, TELNET, etc.

   Transport Layer
       allow any two computers to exchange messages even if
        they come from different vendors and even if they are
        of different platform types
       gives platform independence
       TCP, UDP
        Internet Standards &
   Internet Layer
       allow packets to be routed across multiple routers, even if
        they come from different vendors
       IP

   Data Link Layer
       organize transmissions within a single network
       PPP, Ethernet, etc.

   Physical Layer
       standardize connector plugs, transmission media,
        electrical signaling, and other physical matters you can
        see and touch, even if they come from different
       modem, telephone wire, wall jack, etc.
        OSI Application Layer (OSI Layer 7)

   For Communication Between Specific Types of
    Application Programs
      Email-Email

      Database-Database

   Not Widely Used
      Sometimes simplified then adopted by IETF as a

       TCP/IP standard
   Similar to TCP/IP Application Layer
      But not exactly the same
          OSI Presentation Layer (Layer 6)

   For Standards Used in Multiple Applications
      Standards for text formatting

      Standards for graphics formatting

      No need to create for each application

   To Provide a Generalized Way to Represent Data
      Abstract Syntax Notation 1 (ASN1)

      Allows for exchanges between machines with

       different ways of representing data
   Nothing Like this in TCP/IP
         OSI Session Layer (OSI Layer 5)

   Provides a Connection Between Application
    Programs on Different Machines
       If the connection is broken, it can be reestablished
       In general, standards at this layer manage
        exchanges between application programs

   TCP/IP Transport Layer Provides Some of this
                     Session (5)
                    Transport (4)       Transport
      OSI Transport Layer (OSI Layer 5)

   Provides Connection Between Different Machines
      Needed because machines may be of different

       platform types
   Similar to TCP/IP Transport Layer
      But TCP/IP transport layer also provides some of

       the functionality of the OSI Session layer

                     Session (5)
                    Transport (4)        Transport
        OSI Network Layer (OSI Layer 3)

   The Most Difficult to Characterize
   Originally Created for single networks that had a
    mesh of switches
      Defined a route within a single network
       OSI Network Layer (OSI Layer 3)

   ISO and ITU-T “Forgot” to Have an Internetting
      Internetting--routing across singal networks was

       later added to Layer 3
   So OSI Networking Layer is for BOTH within a single
    network and Routing Across single networks
      Inelegant
       OSI Network Layer (OSI Layer 3)

   However, OSI Only Developed One Three-Layer
    Single Network Standard (X.25)

   So in practice, OSI Layer 3 is an Internetting Layer

                Network (3)           Internet
                Data Link (2)
                Physical (1)
        OSI Data Link and Physical Layers

   We Saw These Earlier
   Data Link Layer (OSI Layer 2)
      Manages the transmission of frames across a

       single link
   Physical Layer (OSI Layer 2)
      For physical and electrical standards within a

       single link

                    Data Link (2)       Data Link (2)
                    Physical (1)        Physical (1)
          OSI Dominance in Single Network

   OSI Standards are Dominant for single networks
      LANs

      WANs

      TCP/IP Does Not Challenge that Dominance

   IETF Generally Does Not Create single network
    Standards for TCP/IP
      If it does (as in the case of the Point-to-Point

       protocol, by the way), it follows the OSI
        Hybrid TCP/IP-OSI Architecture

   As Noted Earlier, Most Firms Today Use a Hybrid
    TCP/IP-OSI Architecture for Most of their Internal
   Application          TCP/IP
   Transport            TCP/IP
   Internet             TCP/IP
   Data Link            OSI
   Physical             OSI
             Internet Standards
   E.g., access Web from home using modem

      App               HTTP                 App
      Trans              TCP                 Trans
       Int        IP           Int   IP       Int
       DL        PPP        DL       ?        DL
      Phy       Modem       Phy      ?       Phy

     User PC              Router          Webserver
            Internet Standards
   E.g., access email from classroom

     App                             POP                  App
     Trans                           TCP                  Trans
      Int              IP                   Int   IP       Int
      DL          Ethernet                  DL    ?        DL
      Phy            NIC                    Phy   ?        Phy

    User PC                             Router         Email server
              NIC: Network Interface Card
        Intranets & Extranets
   Intranets: secure Internet-based communication inside an
       not directly connected to Internet
       firewalls function as gateways to Internet
       uses Internet protocols: TCP/IP, DNS, etc.
       has internal IP addressing scheme
       Virtual Private Networks

   Extranets: secure links between business partners, Internet-
     Network Components
   Hardware
      Computer

      Network Interface Card (NIC)

      Hub

      Switch

      Bridge

      Router

      Etc.

   Software
      Communication protocols: e.g., HTTP, IP

      Network management protocols, e.g. SNMP

      Etc.

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