Communications and Networks Chapter 8 in Discovering Computers Fundamentals

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Communications and NetworksChapter 8 in
Discovering Computers Fundamentals
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Quick Overview of Some of the Main Points

• Communications
• Uses of Communications
• Communication Channel/Transmission Media
• Transmission Characteristics
• Different type of lines
• Communication Devices
• Networks

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Uses of Communications

• Communication (in computer terms) is the process
  by which one computer can transfer
  data/information to another computer.
• Telecommunications or Data Communications
• Read about the Uses of Computer Communications
  DCF p.297
• Communication is a combination of software and
  hardware

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Network

• At work, you might have a printer connected to
  your computer. If you were in a network, you
  could allow your co-workers access to your
  printer. The printer is the resource that you are
  sharing.
• A network is collection of computers and devices
  connected together via some method to allow
  users to share resources.
• Those methods are discussed in this chapter.

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Internet

• The internet is the worlds largest network.
• When you request to see a website, the web page
  (the electronic document) is being sent to your
  computer through the internet.
• How is that information being sent? Via telephone
  lines? Via satellites?

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More on Network

• VERY important to read the Networks section on
  page 303
• It explains the advantages of a network very
  well!!!!!!!!!!

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Networks

• Know the difference between
• LAN
• Peer-to-peer lan network
• Client/Server network
• WAN
• Internet peer-to-peer network
• MAN

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Topologies

• Ok, so you are going to have a network. How are
  you going to physically connect them?
• Make sure and read book on topologies for more
  information, but here are the three major ways

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Topologies of networksSEE DIAGRAMS IN BOOK

• The physical layout of the hardware
• Bus consists of a single central cable to which
  all devices are connected to
• Ring cable to which devices are connected to
  forms a closed ring
• Star all devices on the network are connected to
  a central computer, thus forming a star

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Protocols

• Now that the computers are physically connected,
  you have to make sure that they all follow the
  same rules or protocols.
• A protocol is a set of rules and procedures for
  exchanging information among computers.

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More on Protocols

• This is a confusing topic because some computers
  use many different types of protocols
• Think of rules. We dont all follow one set of
  rules. We follow one set of rules for driving,
  and another set of rules at the workplace, etc
• Computers follow different rules depending on
  what they are trying to do and who they are
  trying to communicate with.
• I have two computers at home connected together
  in a mini-network. They use a certain protocol in
  order to communicate with each other. However,
  when they communicate on the internet, they use
  another protocol.

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TCP/IP

• Information travels on the internet in packets.
  Each web page, for example is broken into many
  packets. Each packet has the destination address,
  and is labeled as 1 of 3, etc The destination
  computer, when it receives the packets
  reassembles them and then displays the
  information. Both computers have to follow a
  certain rule/protocol in order for it to work.
  This protocol is TCP/IP.
• TCP/IP is a widely used protocol on the internet.
  It defines how to break the message into packets,
  how to reassemble the message, what to do if some
  of the packets get lost, etc
• A router is a device that routes these packets
  through the network.

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Token Ring and Ethernet

• These are two other protocols discussed in the
  book. These protocols determine how computers
  have access to a LAN (local area network).
• For example, on a network, a computer/device
  cannot just send information at any given time.
  They basically have to take turns. There are
  rules that govern this and they all have to
  follow the same rules.
• If every computer on a network sends out its
  information at the same time, you would probably
  have too many collisions and the information
  basically gets lost. The computers then have to
  resend the information.

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More on Token Ring

• Token Ring is a protocol that is normally used in
  a ring topology or star topology.
• If you set up your computers in a ring, this is
  probably the protocol you would use.
• This protocol requires that a special signal or
  token is passed from one device to another. The
  device that has the token can transmit on the
  network. There are few collisions since they each
  take turns.

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More on Ethernet

• Ethernet is a protocol that is normally used in a
  bus topology or star topology.
• This protocol requires that the computers peak
  onto the network and if it senses that there is
  information being sent by someone else, it waits.

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More on protocols

• Understand that there are many protocols out
  there, depending on what you are trying to do.
• HTTP is the protocol used for transferring web
  pages
• SMTP is a protocol used for delivering email
  messages
• Ethernet/Token Ring are protocols used to
  determine when a computer has access to the
  network
• Once we figure out when the computers are going
  to have access to the network, we can use TCP/IP
  protocol to manage the transmission of how that
  data gets sent from one computer to the other.
• Your computer can follow TCP/IP AND ETHERNET
  protocols they are for two different purposes.

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Firewall

• Understand what a firewall is!!!!!!!!
• A firewall prevents outsiders into a network.
• If you use DSL or Cable Modems, you should have a
  firewall program installed on your computer also
  to prevent people on the internet from
  accessing your computer!!!

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Internet vs. Intranet

• This is the book!!!!!!!!!!!
• An Intranet looks similar to what you see on the
  internet but it is limited to one particular
  location (a company).
• A companys intranet is a set of web pages only
  accessible within the company!!!!!!!!

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Dial-Up Lines vs. Dedicated Lines

• Dial-Up lines
• Telephone lines
• Only has a connection while call is in use
• Dedicated lines
• Always a connection (24 hours a day)
• Sometimes companies dont want to buy their own
  lines, so they LEASE them.
• Can use telephone lines or can use other lines
  (like cable lines)
• Cable Modem and DSL are dedicated
• When you have dedicated lines you should think of
  getting a firewall (more info in book)

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Communication Devices

• Types of hardware/equipment that transmits
  data/information onto the transmission media.
• You might have the phone line plugged into your
  computer, but you need something to send the data
  out on the phone line modem
• Modem - converts the computer digital signal to
  an analog signal so it can travel over the phone
  lines. Generally they transmit data between 28.8
  Kbps and 56 Kbps
• Cable Modem - sends computer signal over cable
  lines. They generally transmit data between 500
  Kbps and 2Mbps (2Mbps is approx. 2000Kbps).

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Transfer Rates

• Whenever we are referring to the speed at which a
  line carries data (i.e., how fast can we send
  info on the internet from our computer at home)
  we are referring to transfer rate.
• Transfer rate always uses the bps unit (bits per
  second). Generally we refer to it as Kbps
  (kilobits per second).

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More on Transfer Rates

• FYI you dont need to know how to do this, but
  say you have a 56 Kbps internet connection, how
  long does it take to download a 1MB file??
• Well, 1 megabyte approx. 1 million bytes
• 1 million bytes 8 million bits
• 56Kbps approx. 56000 bits per second
• 8,000,000/56000 approx. 153 seconds
• 153 seconds approx 2.4 minutes!

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More on The Telephone Network

• Dial-Up lines
• Uses standard telephone lines
• Remember, telephone lines require information in
  analog frequencies
• Modem translates digital (computer signal) on
  phone line into analog frequency so that it can
  be sent on phone line

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Even More on The Telephone Network

• DSL
• Uses standard telephone lines
• However, it uses a different sending device
  (instead of a regular modem it uses a DSL modem).
• The DSL modem sends out the information
  digitally. Special technique which allows us to
  use regular phone lines, in a digital way, which
  allows the information to be sent faster.
• ADSL is slower than SDSL.
• ISDN
• Read about it in book!!!!!!!!!!! Uses telephone
  lines, and also sends out info digitally. Uses
  and ISDN modem. This technique is older and not
  as fast as DSL!

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And Yet Even More on The Telephone Network

• Cable Lines
• Does not use telephone lines
• Uses cable lines
• Comparable to DSL, though some say its faster
• Read about T-carrier and ATM lines
• Read about modems on page 9.28-9.29!!!!!!!!!!

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Connecting Networks

• The internet consists of many small networks
  connected together.
• A hub is a device that provides a central point
  for cables in a network, see figure on 9.30.
• A router (as stated earlier) is a device that
  receives packets on a network and routes them to
  their destination!

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Communication Channel

• A communication channel is the path that
  information takes when it is transferred from one
  computer to another.
• For example, if you were going from Houston to
  Hawaii, your channel would be ALL the different
  ways/roads you used to get there (road to get to
  highway, highway to get to airport, air to get
  to Hawaii, road to get to hotel).

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Internet Communication Channel

• If you were requesting information from the
  www.whitehouse.gov website, that information
  might have to go through telephone lines, then
  fiber optic cables, then satellites, then back
  through phone lines, in order to get to your
  house. That is the communications channel your
  information traveled on.

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Transmission Media

• BANDWIDTH is the width of the communication
  channel. The higher the bandwidth, the more data
  and information the channel can transmit.
• What can we use that will carry that
  information/signal from one computer to another?
  Cables? Satellites? What?
• Transmission media consists of the materials or
  techniques capable of carrying a signal.

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PHYSICAL TRANSMISSION MEDIA

• Physical cables
• Twisted-Pair Cable (phone cables)
• Coaxial Cable (cable companies use this)
• Fiber-Optic Cable (Much of the internet backbone
  uses this)
• Most companies use Twisted-Pair cables in their
  buildings. Cheap, and easy to install.
• Most of the internet backbones use Fiber-Optic
  cable. Not much noise (interference), fast, but
  expensive and hard to install.
• Coaxial cable is in the middle.

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WIRELESS TRANSMISSION MEDIA

• Broadcast Radio
• Cellular Radio
• Microwaves
• Expensive to install, and not as fast as some of
  the other physical media, but useful when its
  too difficult to install cables
• Must have line-of-sight (read book for more info)
• Satellites (Very expensive)

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Recap on Transmission Media

• So, back to our example. If you are trying to
  view the www.whitehouse.gov website, the web page
  information must be sent through the internet to
  your computer.
• What path (communication channel) does it take
  (i.e., what transmission media does it go
  through)?
• The information probably travels on twisted pair
  cable out of the whitehouse.gov computer, then
  onto some fiber optic cable, maybe bounces off a
  couple of microwaves, maybe back to fiber optic
  cable, then back onto twisted pair cable and into
  your home.

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Summary

• There are many parts to a network
• Transmission media physical vs. wireless
• The cables or satellites that information travels
  through
• Communications devices equipment that send out
  the info on the transmission media
• Two different networks can use the same
  transmission media (twisted pair cable), but
  depending on the communications device, software,
  techniques, the information can travel faster on
  one network than the other.
• Topologies how do we physically connect the
  computers.
• Protocols rules that the computers must all
  follow in order to send the information. TCP/IP
  is a protocol.

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The End