Docstoc

Ch1 - Wenli Wangs homepage

Document Sample
Ch1 - Wenli Wangs homepage Powered By Docstoc
					      Chapter 1

Introduction to Computer
   Networks and Data
    Communications
        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
         Communication

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




       Sender      Signal      Receiver

                Transmission
                  medium
Communication Problems

   Completeness & comprehension
   Attenuation & noises
   Competing resources
   Routing & addressing
   Security
               Networks
   Computer network
   Voice network
   Data network
   Local area network (LAN)
   Metropolitan area network (MAN)
   Wide area network (WAN)
   Personal area network
   Etc.
                    Datacom
   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
   LAN-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
   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
           fails
The OSI Model

   Application
   Presentation
     Session
    Transport
    Network
     Datalink
     Physical
      Logical vs. Physical
          Connection

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




                                Application
                                 Transport

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

     Physical

                                Application

                                 Transport
                                  Internet
                        Single Network   Data Link
                              OSI
                           Standards     Physical
OSI vs. The Internet

  Application
                Application
 Presentation

   Session

  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 &
              Protocols
   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 &
              Protocols
   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
        vendors
       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
    Functionality
                                       Application
                     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


                                        Application
                     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
    Layer
      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)
                                       Subnet
                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
    Transmission
      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
       architecture
        Hybrid TCP/IP-OSI Architecture

   As Noted Earlier, Most Firms Today Use a Hybrid
    TCP/IP-OSI Architecture for Most of their Internal
    Communication
   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
    enterprise
       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-
    based
     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.

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:3
posted:6/5/2010
language:English
pages:31