Computer Network

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Computer Network
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• What is a Network?
• A computer Network is a set of two or more
  interconnected computers and a set of hardware
  devices.
• Need for Networking
• Resource Sharing
• Reliability
• Cost Factor
• Communication medium
• Application of Network
• Sharing Peripherals and data sharing
• Access to remote database

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• Communication facilities
• Elementary Terminology of Networks
• Nodes (Workstations) - Nodes refers to the
  computer that are attached to a network
• Server A computer that facilitates the sharing
  of data, software and hardware resources (e.g.
  Printer, modem etc) on the network is termed as a
  server.
• Server is of two types
• Non Dedicated Server 2- Dedicated Server
• Non Dedicated Server - The Server serves both as
  a workstations and server. Such Network is known
  as peer- to peer network
• Dedicated Server - On bigger network a computer
  is reserved for servers job and its only job is
  to help workstation access data , software and
  hardware. The network using such a server are
  known as Master- Slave networks

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• Network Interface Unit NIU(MAC Address)
• A Network Interface Unit is an interpreter
  that helps establish communication between the
  server and workstation.
• A unique number identifying workstations
  attached is known as node address
• NIU is otherwise called TAP (Terminal Access
  Point) or otherwise Network Interface Card NIC
• MAC (Media Access Control) Refers to the physical
  address assigned by NIC manufacturer. MAC address
  is a 6-byte address of which first 3 are the
  manufacturer-id and last 3 bytes are the card
  no.
• IP Address Every machine on a TCP/IP network
  has a unique identifying number called IP Address

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• Domain Name - It is a unique name assigned to a
  website. It contains three parts www, name
  describing the websites purpose and TLD(Top
  Level Domain) Such as .com,.net, .org .in etc.
• Domain names are internally converted into
  IP Address before a communication can happen.
• Domain Name Resolution refers to the process of
  obtaining corresponding IP address from a domain
  name.

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• NETWORK TOPOLOGIES
• The pattern of interconnection of nodes in a
  network is called the Topology
• Factors to consider in choosing the Topology
• Cost
• Flexibility
• Reliability
• Types of Topologies
• Point to- point Link
• The main characteristic of P-P network is that
  each station receives exactly from one
  transmitter and each transmitter transmits to
  exactly one receiver.

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• The Star Topology

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• This topology consists of a central node to which
  all other nodes are connected by a single path.
  The star topology has found extensive application
  in area where intelligence in the network is
  concentrated at the central node.
• Advantages Ease of service, One device per
  connection, Centralized control/Problem diagnosis
  and Simple access protocol.
• Disadvantages Long cable length , Difficult to
  expand and Central node dependency

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The bus or linear Topology
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• The simplest form of a physical bus topology
  consists of a trunk (main) cable with only two
  end points. When the trunk cable is installed, it
  is run from area to area and device to
  deviceclose enough to each device so that all
  devices can be connected to it with short drop
  cables and T-connectors.
• The principal advantage of this topology is cost
  no hubs are required, and shorter lengths of
  cable can be used. It is also easy to expand.
  This simple "one wire, two ends" physical bus
  topology is illustrated in Figure
• Disadvantage Fault diagnosis is difficult,Fault
  isolation is difficult, Repeater Configuration.

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The Ring or Circular Topology
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• It is a closed network structure in the form of
  a circle, to which all nodes are connected. The
  ring name comes from the design of the central
  network device, which has a loop inside it to
  which are attached cables for all the devices on
  the network. MAU(Media Access Unit).

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The Tree Topology
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• A variation of bus topology is tree topology. It
  is also called a "hierarchical" topology, tree
  topology is a combination of bus and star
  topologies. Nodes are connected in groups of
  star-configured workstations that branch out from
  a single "root". The root node usually controls
  the network and sometimes network traffic flow.

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Graph Topology
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• The nodes are connected together in an arbitrary
  fashion. A link may or may not connect two or
  more nodes. There may be multiple links also.

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Mesh Topology
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• Mesh networking is a type of networking wherein
  each node in the network may act as an
  independent router, regardless of whether it is
  connected to another network or not. It allows
  for continuous connections and reconfiguration
  around broken or blocked paths by hopping from
  node to node until the destination is reached. A
  mesh network whose nodes are all connected to
  each other is a Fully connected
• The primary advantage of this topology is that it
  is highly fault tolerant when one node fails,
  traffic can easily be diverted to other nodes.

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• Types of Networks
• Computer Networks are classified on the basis of
  geographical spread, There can be four types of
  Network
• Local Area Network (LANs)
• Metropolitian Area Networks (MANs)
• Wide Area Networks (WANs)
• Personal Area Network (PANs)

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• Local Area Network (LANs)
• Local Area Networks (LAN) is a number of devices
  (Computers, Printers, Fax) that are connected to
  each other by some form of wiring, within a
  localized area (within building e.g. a school,
  an office etc. ) to share data and resources. A
  LAN enables independent devices to communicate
  directly with each other through direct
  communications.
• Metropolitan Area Networks(MANs)
• In a Metropolitan Area Network computer connected
  to each other with in a city to have the
  organization concentric needs. Though the
  distance between the devices is not very large,
  they can have their own cabling plan.

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• Wide Area Network(WANs)
• Wide Area Networks (WAN) is a number of local
  area networks that are connected to form a large,
  logical network without any geographical
  limitation. WANs can be close together
  physically or separated by a large distance.
  WANs can share a large numbers of resources, or
  they can have different big network.The largest
  WAN in exsistence is the Internet.
• Personal Area Network (PAN)
• A Personal Area Network refers to a small network
  of communication- capable devices with in a range
  of reachability of an individual person. The
  range is typically up to 10 meters.

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Comparison LAN and WAN

LAN WAN
Diameter of not more than a few Kilometers A total data rate of at least several mbps Complete ownership by a single organization very low error rates Span entire Countries Data rate less than 1 mbps Owned by multiple organizationComparatively higher error rates
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TRANSMISSION MEDIA

• When data is sent across the network it is
  converted into electrical signals. To be sent
  from one location to another, a signal must
  travel along a physical path. The physical path
  that is used to carry a signal between a signal
  transmitter and a signal receiver is called the
  transmission medium. There are two types of
  transmission media guided and unguided.
• Guided media includes cables. Unguided media
  includes waves through air(microwaves, radiowaves
  and satellites) Basic types of cable for guided
  media is discussed below

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Twisted Pair Cable

• Twisted-pair wiring refers to a type of cable
  composed of two (or more) identical wires twisted
  around each other within a plastic sheath. The
  wires are twisted to reduce crosstalk (The
  bleeding of a signal from one wire to another and
  which can corrupt signal and cause network
  errors. This form of signal interference is
  called Crosstalk). There are "shielded" and
  "unshielded" varieties of twisted-pair cables.

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• Advantage 1.It is simple.
• physically flexible.
• Very inexpensive.
• Can easily be connected
• Disadvantage 1.Because of high attenuation it is
  incapable to carry signals for long
• distance without
  repeaters.
• 2.Low bandwidth capabilities make it unsuitable
  for broadband applications
• 3. It support maximum data rate 1 Mbps to 10 Mbps

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2. Coaxial Cable

• This type of cable is referred to as coaxial
  because it contains one copper wire (or physical
  data channel) that carries the signal and is
  surrounded by another concentric physical channel
  consisting of a wire mesh or foil. The outer
  channel serves as a ground for electrical
  interference. It is better than twisted pair

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• Advantage better than twisted pair,can be used
  for broadband transmission (can be used with
  Cable TV) , bandwidth upto 400 MBPS
• Disadvantage Expensive compared to twisted pair
  cables , Coaxial is not compatible with twisted
  pair cables.

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3. Optical Fibers

• Optical fibers consist of thin strand of glass
  like material which are so constructed that they
  carry light from a source at one end of the fiber
  to a detector at the other end.

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• Advantage 1.immune to magnetic interference.
• 2. Highly suitable for harsh industrial
  environment
• 3. guarantees secure transmission
• Disadvantage 1. Installation problem
• 2. Fiber optic cable are more difficult to
  solder
• 3. They are the most expensive of all cable

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• Unguided Media
• Microwave and Radiowave
• Radio Waves are low levels of transmission power
  for signals to and from your phone. These
  non-ionizing frequencies of radiation are safe.
  However as signal strength grows from a few
  hundred MHZ of power to beyond 800 MHZ, the
  electromagnetic spectrum increases and these
  waves become microwaves.

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• Advantages
• It is cheaper then the guided media, and require
  less maintenance.
• It cover large distance With 100meter high tower
  distance of 100 Km between towers are feasible.
• Disadvantages
• It is unsecured medium of communication.
• The loss of signal is more as compared to guided
  media.
• Its communication depend up on the atmospheric
  conditions.

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• satellite
• Satellite communication is special case of
  microwave relay system. In satellite
  communication the earth station consists of a
  satellite dish that functions as an antenna and
  communication equipment to transmit and receive
  data from satellite passing over head.
• Advantage The area covered is quite larger
• Disadvantage Technological limitations
  preventing the development of larger, high gain
  antennas on the satellite platform

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• Infrared
• This type of transmission is used in TV remotes,
  wireless speakers etc. It transmits data through
  air and can propagate throughout a room.

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• Laser
• The Laser transmission requires direct line of
  sight. It is unidirectional like microwave, but
  has much higher speed than microwave . Laser
  transmission is point to point transmission,
  typically between buildings

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• Bluetooth
• Bluetooth is used to interconnect devices in
  short distance. Bluetooth requires that a
  low-cost transceiver chip be include in each
  device. Mobile phones PDAs can be easily
  interconnected.

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NETWORK DEVICESModem
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• Hub
• A Hub is a multipurpose network device that lies
  at the centre of a network to channel the traffic
  from one computer to another.
• Hubs are of two type
• Active Hub Electrically amplify the signal
• Passive Hub Allow the signal to pass from one
  computer to another

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• Switch
• A switch is a device that is used to segment
  networks into different subnetworks called
  subnets or LAN segments. Prevents traffic
  overloading in a Network
• A Switch is responsible for filtering i.e.
  transforming data ina specific way and forwarding
  packets between LAN segment

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• Repeater
• A Repeater is a network device that boosts the
  power of incoming signals to allow the length of
  a network to be extended.

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• Gateway
• A Gateway is a network device that connects
  dissimilar network. It establishes an intelligent
  connection between a local network and external
  networks with completely different structure.

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• Bridge
• A Bridge is a network device capable of
  connecting networks that use similar protocols.
  It connects two local area networks running the
  same network operating system.
• A bridge allows to cross only that data which has
  valid MAC address of other side of Bridge

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• Router
• A Router is a network device that connects
  multiple networks irrespective of their protocol.
  This is because a router can handle different
  protocol, otherwise it works similar to the
  bridge.
• A Router forwards data packets from one connected
  network to another depending upon their IP
  address and not their MAC address.

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NETWORK SECURITY

• Intrusion Problems/ Access Attacks
• When an unauthorized user attempts to gain access
  to protected sensitive information, it is known
  as Access Attack or Intrusion Problem.This type
  of attack is an attack against confidentiality of
  information.
• Snooping refers to unauthorized access of someone
  elses data, email, computer-activity or data
  communication.
• Eavesropping is the act of secretly listening
  /intercepting someone elses private
  communication/data /information

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• Denial of Service (DoS) Attacks
• Denial of service attacks are those attacks that
  prevent the own users of the system from
  accessing or using resources, information. DoS
  attacks can be of different types-
• Denial of access to information
• Denial of access to Applications
• Denial of access to system
• Denial of access to Communications

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NETWORK SECURITY MEASURES

• Active Protection
• Authorization
• Firewall A system designed to prevent
  unauthorized access to or from a private network
  is called firewall
• Intrusion detection
• Preventive Measures
• Implement proper Security Policy for your
  organization
• Use proper fie access permissions when sharing
  files on the internet
• Disconnect from the internet when away

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• Thank You