Communication and Networking

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Communication and Networking
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Networking

• A computer network is a collection of computing
  devices that are connected in various ways in
  order to communicate and share resources
• Usually, the connections between computers in a
  network are made using physical wires or cables
• However, some connections are wireless, using
  radio waves or infrared signals
• The generic term node or host to refer to any
  device on a network
• A key issue related to computer networks is the
  data transfer rate, the speed with which data is
  moved from one place on a network to another

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Networking

• Computer networks have opened up an entire
  frontier in the world of computing called the
  client/server model
• A file server is a computer that stores and
  manages files for multiple users on a network
• A Web server is a computer dedicated to
  responding to requests (from the browser client)
  for Web pages
• A mail server is a computer that stores email
  messages for multiple users and routes the
  messages to the email clients when a request is
  made.
• Network printers

Client/Server interaction
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Communication Basics

• Properties of Transmission
• Each link has common attributes
• 1. Type of signal communicated (analog or
  digital)
• 2. The speed at which the signal is transmitted.
• 3. The type of data movement allowed on the
  channel.
• 4. The method used to transport the data.
• 5. Single channel and multichannel transmission.

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Communication Basics

• 1. Type of signal communicated.
• Analog - A continuously changing signal similar
  to that found in voice transmission (e.g., phone
  lines).
• Digital - Signals consist of pulses of electrical
  energy that represent 0s or 1s.

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Communication Basics

• MODEM - MOdulator DEModulator
• Outgoing Converts binary data from computer
  (digital) into telephone compatible signals
  (analog).
• Incoming Converts telephone signal (analog) into
  binary data for the computer (digital).

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Communication Basics

• 3. Type of data movement.
• Three types of data movement can occur on a
  channel
• Simplex transmission - One way transmission.
• Half-duplex transmission - Can flow only one way
  at a time.
• Full-duplex transmission - Two-way transmission
  at the same time.

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Communication Basics

• 4. Method of transmission.
• Two types of data transmission, each requiring a
  different modem.
• Asynchronous transmission
• data is sent one byte at a time, with each string
  of bits making up the byte bracketed with special
  control bits
• Synchronous transmission
• data is sent in blocks, with start and stop bit
  patterns (synch bytes) at the beginning and end
  of the blocks

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Communication Basics

• 5. Single channel versus multi-channel
  transmission
• Channel - A path of a signal.
• Single channel - Capable of only
  sending/receiving one signal at a time.
• Phone line - Single line single phone call at a
  time.
• Multi-channel - Capable of more than one channel
  at a time.
• Fiber-optic cable, microwaves, Satellite
  transmissions.

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Communication Basics

• How is it possible to measure the capacity of
  communications links?
• Bandwidth
• In Digital
• Number of bits per second (bps) that can be sent
  over a link.
• Wider bandwidth, the more diverse kinds of
  information can be sent.
• Simplest is voice, most sophisticated is moving
  videos.
• In Analog
• The difference between the highest and lowest
  frequencies that can be sent over an analog link
  (like phone lines).
• Measurement is given in hertz (Hz).
• For both The wider the bandwidth, the more
  information can flow over the channel.

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Communication Basics
Typical cable bandwidths used in local area
networks. Cable Typical Bandwidth Twisted
Pair 10 to 100 Mbps Coaxial Cable 10 to 100
Mbps Fiber-optic cable 100 to 200 Mbps The
bandwidths of different services offered by a
telephone company Service Bandwidth ISDN 64
Kbps T1 1.544 Mbps T3 44.736 Mbps STS-1 51.840
Mbps STS-3 155.250 Mbps STS-12 622.080
Mbps STS-24 1.244160 Gbps STS-48 2.488320 Gbps
Mbps megabytes per second (millions
GbpsGigabytes per second (billions)
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Types of Networks

• A local-area network (LAN) connects a relatively
  small number of machines in a relatively close
  geographical area
• A wide-area network (WAN) connects two or more
  local-area networks over a potentially large
  geographic distance
• Often one particular node on a LAN is set up to
  serve as a gateway to handle all communication
  going between that LAN and other networks
• Communication between networks is called
  internetworking
• The Internet, as we know it today, is essentially
  the ultimate wide-area network, spanning the
  entire globe

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Types of Networks
Local-area networks connected across a distance
to create a wide-area network
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Intranets and Extranets

• Intranet - an organizations internal private
  network that uses the infrastructure and
  standards of the Internet and the WWW
• Extranets - private intranets that connect not
  only internal personnel but also selected
  suppliers and other strategic parties

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Firewalls

• A firewall is a machine and its software that
  serve as a special gateway to a network,
  protecting it from inappropriate access
• Filters network traffic that comes in, checking
  the validity of the messages as much as possible
  and perhaps denying some messages altogether
• Enforces an organizations access control policy

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Types of LAN Topologies (Configurations)

• Star topology
• Centers around one node to which all others are
  connected and through which all messages are
  sent.
• Everything depends on the central host if it
  goes down the whole network goes down.

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Types of LAN Topologies (Configurations)

• Ring topology
• Connects all nodes in a closed loop on which
  messages travel in one direction.
• A message sent out from one node is passed along
  to each node in between until the target node
  received the message.
• More reliable than star network since one machine
  going down does not affect all of the connections.

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Types of LAN Topologies (Configurations)

• Bus topology
• All nodes are connected to a single communication
  line (bus) that carries messages in both
  directions
• Most reliable type of network
• The primary protocol used for bus networks is
  called Ethernet which has become the industry
  standard for local-area networks
• Messages are broadcast across the bus and picked
  up by the recipient
• If two nodes send messages at the same time, this
  results in collision in which case, the
  protocol forces the nodes to wait for a random
  period of time and then retransmit.

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Types of LANs

• Client/server LAN
• Clients - microcomputers that request data and
• Server - a powerful microcomputer that manages
  shared devices

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Types of LANs

• Peer-to-peer LAN
• all microcomputers on the network communicate
  directly with one another without relying on a
  server

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Components of LANs
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Components of LANs
Hub A device that repeats or broadcasts the
network stream of information to individual nodes
( usually personal computers) Switch A device
that receives packets from its input link, and
then sorts them and transmits them over the
proper link that connects to the node addressed.
Bridge A link between two networks that have
identical rules of communication. Gateway A
link between two different networks that have
different rules of communication. Router A node
that sends network packets in one of many
possible directions to get them to their
destination.
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Communication Channels

• Communications channel
• the path (physical medium) over which information
  travels in a telecommunications system from its
  source to its destination
• The physical media used to connect the networks
  are
• Twisted pair
• coaxial cable
• fiber optic cable
• and Wireless channels

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Communication Channels

• Twisted pair
• Two wires twisted together.
• Less susceptible to acting like an antenna and
  picking up radio frequency information or
  appliance noise.
• Used by the telephone company.

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Communication Channels

• Coaxial cable
• One wire is formed into a tube which is
  electrically grounded.
• The other wire is placed down the center of this
  tube and the space between is filled with a
  special nonconducting material.

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Communication Channels

• Fiber-optic cable
• Optical cable allowing light to pass along the
  cable.
• Light is electromagnetic, and because of its
  higher frequencies, transmits a lot more
  information through a single strand.

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Communication Channels

• Three types of wireless communication commonly
  used
• Infrared
• Commonly used in TV and VCR remote controls.
• Use infrared frequencies of electromagnetic
  radiation that behave much like visible light.
• Must be in the line of sight.
• Often used to connect keyboards, mice, and
  printers.
• Radio frequency
• Uses radio frequencies.
• Not commonly used because of the possible
  interference from other sources of
  electromagnetic radiation.
• Microwave
• Often used to communicate with distant locations.
• Must be line of sight.
• Satellite communications use microwaves.