Networking Basics

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Chapter 2

• Networking Basics

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Objectives

• In this chapter, you will learn to
• Illustrate the different types of computer
  networks
• Describe LAN transmission media
• Discuss physical and logical LAN topologies
• Explain the network services provided by LANs
• Identify standards organizations and their role
  in setting standards
• Describe the Seven-Layer OSI Model

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Types of Computer Networks
Valued Gateway Client

• A computer network consists of
• Two or more computers, as well as
• Other devices such as printers or faxes connected
  by some form of data transmission media such as a
  cable
• Network Operating Systems provide network
  services including
• File management
• Security
• Resource management
• Computers and network devices use a Network
  Interface Card to connect with the network

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Local Area Networks (LANs)

• LANs
• Are limited to a small geographic area, such as
  an office or a building - will not use the public
  telephone system
• Have two basic architectures
• Peer-to-peer
• Client/server
• Each computer has its own processing
  capabilities, but can access files on other
  computers, network printers, and use network
  services
• Each computer or destination device on the
  network is also known as a node - nodes are 'self
  aware' of the network(s) to which they belong

what's the difference? and why do you care?
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Peer-to-Peer Networks

• Usually consist of six or fewer general-purpose
  personal computers
• Computers communicate with each other and share
  the same files and devices
• Every computer on a peer-to-peer network is
  equal, that is, no one computer is in charge of
  the other computers
• Does not require a special Network Operating
  System - but note that microcomputer operating
  systems since Windows 2000 and Windows XP
  incorporate network capabilities

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Peer-to-Peer Network

• All computers are connected to one main cable
  (also called the backbone)
• Simplest option when connecting two or three
  devices

what happens if the backbone breaks?
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Peer-to-Peer Network with a Hub

• All computers are connected through a common
  connection point (Hub)
• Can connect more computers and devices to a
  network than a backbone
• can be 'daisy chained' but this is inefficient

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Peer-to-Peer Network with a Hub
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Peer-to Peer NetworkAdvantages/Disadvantages

• ADVANTAGES
• Simple and inexpensive network solution
• Does not require special Network Operating System
• Simplicity of administration

• DISADVANTAGES
• Not practical for more than five or six computers
• Limited or no security
• Business may quickly outgrow network

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Client/Server Network

• Consists of general-purpose personal computers
  which are called clients and special
  high-performance computers called servers - there
  is no special need for the 'server' to have any
  more or less power than the clients
• Servers enable clients to
• share data
• store data
• provide support for network services, such as
  e-mail
• Requires a special network operating system such
  as Microsoft Windows 2000 Server, UNIX, or Novel
  NetWare (Novel has a smaller part of today's
  market of network operating systems)

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Client/Server NetworkArchitecture
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Client/Server NetworkAdvantages/Disadvantages

• ADVANTAGES
• Centralizes management of network services in one
  location
• Increased security
• Support for greater number of computers, devices

• DISADVANTAGES
• Requires more complex setup and management
• Administration requires higher level of technical
  expertise
• More expensive to implement

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Metropolitan Area Network (MAN)
few people use the term "MAN" anymore, it is just
a 'longer' LAN that does note interface with the
public telephone system

• A high-speed network connecting two or more LANs
• A MAN is usually confined to a single
  metropolitan area, such as a large city and its
  suburbs

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Wide Area Network (WAN)

• Spans a larger area than a MAN and consists of
  two or more connected LANs
• The Internet is a very complex and extensive WAN

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LAN Transmission Media

• Transmission media are the means for carrying
  data from one node on a LAN to another node
• Transmission media is divided into two types
• Cable
• Wireless

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Coaxial Cable (coax)

• High-capacity communications and video cable
• Has an insulated solid or stranded wire
  surrounded by a solid or braided metallic shield,
  wrapped in a plastic cover
• Carries heavy network traffic at high speeds
• Provides resistance to interference called noise

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Twisted-Pair Cable

• Consists of insulated copper wires twisted around
  each other in pairs and then enclosed in a
  plastic covering
• Two most common types are shielded and unshielded
• By far the most prevalent medium today for LANs

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Fiber-optic Cable

• Used to carry voice, video, and data signals for
  very long distances without requiring 'repeaters'
• Contains one or more glass fibers at its core,
  surrounded by a layer of glass cladding and a
  protective outer jacket

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incorrect representation, should be four groups
of twisted pairs for 8 total wires
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Infrared (IR) Transmission

• Relies on electromagnetic waves with a frequency
  range above that of microwave but below the
  visible spectrum
• solid objects block the transmission
• Infrared signals are transmitted through space in
  the same way a TV remote control device sends
  signals across a room

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Radio Frequency (RF)Transmission

• Relies on signals sent over a specific frequency,
  like radio broadcast
• not blocked by solid objects (but a solid object
  lessens signal strength)
• RF transmissions are regulated by the Federal
  Communications Commission (FCC) which licenses
  frequencies by geographic location to ensure that
  multiple transmitters do not interfere with each
  others transmissions

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Traveling at the Speed of Data

• Throughput Amount of data that can be
  transmitted within a specific time period
• Measured in units of bits per second (bps)
• 1 Kbps 1,000 bits per second
• 1 Mbps 1,000,000 bits per second 1,000Kbps
• 1 Gbps 1,000,000,000 bits per second 1,000
  Mbps
• Throughput for most (Ethernet) networks is
  between 10 Mbps and 100 Mbps
• Current media (category 7 twisted pair) runs
  1Gbps (i.e. 1,000Mbps) with 10Gbps available but
  network interface cards of 10/100Mbps are the
  most common

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Physical Topologiesof Local Area Networks

• Physical topology refers to a networks physical
  layout or the pattern in which its devices and
  cabling are organized
• Three basic physical topologies
• Bus
• Ring
• Star
• Modern LANs generally combine these topologies
  into a hybrid topology

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Bus Topology

• Used on peer-to-peer LANs
• Consists of a single coaxial cable called a trunk
  (or backbone) to which all devices are connected
• Because the cable is shared, it carries only one
  transmission at a time

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Data Transmissions

• Data transmissions involving one sending and
  receiving node are called point-to-point
  transmissions
• Transmissions that involve one sending node and
  multiple receiving nodes are called broadcast
  transmissions

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Ring Topology

• Each node is connected to the next node via a
  single circle of twisted-pair or fiber-optic
  cable
• Data transmissions travel around the circle in a
  clockwise direction, passing through each node
• When a node receives a transmission, it accepts
  the data addressed to it and then forwards the
  transmission on to the next node

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Star Topology

• Each node is connected to a central hub by a
  separate twisted-pair or fiber-optic cable
• Data is transmitted from one node, through the
  hub, and out again to the destination node

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Hybrid Topology

• Contains elements of two or more physical
  topologies
• Star-wired ring topology is the most common
  hybrid
• Data travels in a circle, from one node to the
  next, but each transmission passes through the hub

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Logical Topologiesof Local Area Networks

• Logical topology defines the way in which the
  data is transmitted between computers
• Specifies several network characteristics
  including
• The access methods, or rules, the nodes follow to
  access the transmission media
• The networks physical topology
• The networks transmission media
• The data throughput rate
• Logical topologies commonly used on LANs are
  Ethernet and Token Ring (actually, token ring is
  much less common)

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Ethernet

• Uses Carrier Sense Multiple Access with Collision
  Detection (CSMA/CD) access method, which directs
  transmission traffic over the network
• All stations attached to the Ethernet are
  "listening" and the station with the matching
  destination address accepts the frame and checks
  for errors
• Collisions
• If two nodes simultaneously check and then
  transmit, their two transmissions collide
• In this case, both nodes immediately stop
  transmitting, wait a random interval, recheck,
  and then rebroadcast

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Token Ring

• A network access method that uses a continuously
  repeating 3-byte frame (the token) that is
  transmitted onto the network by the controlling
  computer
• The token moves clockwise in a circle from node
  to node
• When a node wants to send a message, it waits for
  an empty token then fills it with the address of
  the destination node and some or all of its
  message
• Every node on the network constantly monitors
  passing tokens to determine if it is the
  recipient of a message, in which case it "grabs"
  the message and resets the token status to empty

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Network Services

• Programs that manage data and operations on a
  network, and provide services to multiple users
• Network services include
• File services
• Print services
• Mail services
• Communications services
• Internet services
• Management services

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File Services

• Permit centralized storage of data files
• A high-speed computer in a network stores the
  programs and data files shared by users
• A file server acts like a remote disk drive
• Data stored on a file server can be accessed by
  authorized users around the network

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Print Services

• Enable employees to share printers across a
  network
• Print services include storing print-image output
  from all users of the system and feeding it to
  the printer one job at a time
• A print server provides this service for one or
  more printers in a network
• The print server function may be software that is
  part of the network operating system or an add-on
  utility

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Using NetworkFile and Print Services

1. Document is created and stored on the file server
2. Second user can retrieve document from file
   server then edits and saves file on the file
   server
3. Remote user can retrieve document from file
   server
4. Sends document to network printer

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Mail Services

• Manages the sending, receiving, routing, and
  storage of e-mail
• Controlled by a mail server, usually a computer
  in a network that provides "post office"
  facilities
• Mail services include storing incoming mail for
  distribution to users and forwarding outgoing
  mail through the appropriate channel
• The software that performs this service may
  reside on a computer providing other services

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Communications Services

• Enables traveling employees (remote users) to
  connect to the network and access their data
  files and e-mail messages
• Company LAN is accessed using POTS (plain, old
  telephone system) or ISDN modem, or broadband
  connection through a remote access server, or
  wireless, or any other communications medium

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Using NetworkMail and Communications Services

1. User e-mails a document to a co-worker for
   editing
2. Second user edits the document, then e-mails copy
   to the remote user
3. Remote user connects to network, then retrieves
   document from e-mail
4. Remote user edits document, then e-mails document
   to the original user

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Internet Services

• Provides external Internet access, internal
  intranet services, and management of
  Internet-related technologies such as Web
  servers, Web browsers, and Internet-based e-mail
• Used to establish and manage external business
  Web sites to sell products and services, provide
  customer support, and gather information about
  potential customers and the marketspace
• Internet-based e-mail allows businesses to
  maintain contact with customers and suppliers

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Network Management Services

• Enables administrator to monitor network
  activity, manage user access and network
  resources
• Includes diagnostic and management tools for
  troubleshooting problems and gathering statistics
  for administration and fine tuning
• Centralized installation of software and backup
  of stored data

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The Role of Standards Organizations

• A standard is a rule, description, or design
  approved by an established organization or
  accepted by an industry through common usage
• Networking standards that cover the formatting
  and transmission of data are set by third-party
  organizations that include government agencies,
  scientists, research institutions, consumer
  groups, engineers, manufacturers, vendors, and
  other interested parties

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International Organization for Standardization
(ISO)

• A global alliance drawn from approximately 140
  countries
• Establishes and publishes standards that help
  make possible the international trade of goods
  and services
• Standards govern areas such as photographic
  equipment and film speed, quality management,
  environmental management, freight container, and
  paper size

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• International Electrotechnical Commission (IEC)
• Promote international standards in fields of
  electronics, magnetics and electromagnetics,
  electroacoustics, multimedia, and
  telecommunications
• Works with ISO to develop standards for the IT
  industry
• ANSI - American National Standards Institute
• Non-profit organization that represents the U.S.
  to international organizations such as ISO and
  IEC
• Promotes adoption of U.S. and international
  standards that make U.S. businesses more
  competitive in global markets

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Additional Standards Organizations

• Electronic Industries Alliance (EIA)
• Develops standards for electronic components,
  consumer electronics, and telecommunications
• Institute of Electrical and Electronics
  Engineers, Inc. (IEEE)
• Internal authority on biomedical technology,
  consumer electronics, computer engineering,
  electric power, aerospace, and telecommunications

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Additional StandardsOrganizations

• International Telecommunications Union (ITU)
• International forum for government agencies and
  industry representatives
• Develops standards for telecommunications
• European Telecommunications Standards Institute
  (ETSI)
• European standards organization in the areas of
  telecommunications, broadcasting, and information
  technology

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Open Systems Interconnection(OSI) Model

• An ISO standard for worldwide communications that
  defines a framework for implementing protocols in
  seven layers
• Control is passed from one layer to the next,
  starting at the application layer in one station,
  proceeding to the bottom layer, over the channel
  to the next station and back up the hierarchy

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Open Systems Interconnection(OSI) Model
hubs are at level 1, routers act at level 3,
switches act at levels 2 3
7 6 5 4 3 2 1
7 6 5 4 3 2 1
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Physical Layer (1)

• SENDING NODE
• Passes bits onto the connecting medium

• RECEIVING NODE
• Receives bits from the connecting medium

• Defines the physical and electrical
  characteristics of a system

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Data Link Layer (2)

• SENDING NODE
• Subdivides data into frames, and then transfers
  without errors
• Retransmits frames if acknowledgement is not
  received

• RECEIVING NODE
• Reassembles the frames, performs error checking,
  then acknowledges receipt of the data

• Ethernet technologies work at the Data Link layer

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Network Layer (3)

• SENDING NODE
• Determines best route to receiving node
• Translates IP addresses to MAC addresses
• Segments frames into smaller units

• RECEIVING NODE
• Reassembles the segmented frames

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Transport Layer (4)

• SENDING NODE
• Breaks long frames into smaller units
• Assigns sequence numbers to each unit

• RECEIVING NODE
• Uses the sequence numbers to reassemble units in
  correct order
• Acknowledges error-free receipt of frames

• Ensures frames traveling between nodes arrive
  without error

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Session Layer (5)

• SENDING NODE
• Sets up session with the receiving node
• Decides which nodes can communicate and for how
  long
• Restarts terminated sessions when necessary

• RECEIVING NODE
• Acknowledges session request from sending node
• Maintains communications with sending node

• Establishes and maintains communications between
  the sending and receiving node

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Presentation Layer (6)

• SENDING NODE
• Formats data sent to receiving node for network
  use
• Compresses data into the smallest number of bits
• Can also encrypt data

• RECEIVING NODE
• Formats data received from the sending node for
  application use
• Decompresses data received from the network
• Also decrypts encrypted data

• Formats data for network and application use

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Application Layer (7)

• SENDING NODE
• Translates data received from the application
  into a format recognized by the Presentation layer

• RECEIVING NODE
• Translates data received from the Presentation
  layer into a format recognized by the Application
  layer

• Enables the user applications to access network
  services such as e-mail, file services