CCNA Discovery Chapter Four

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CCNA DiscoveryChapter Four

• By
• Chief Eng. Amna Ahmed
• Institute of Telecommunication
• amna_ahmed28_at_yahoo.com

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Chapter 4

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Explain what the internet is

• Every day millions of people exchange information
  through the Internet - but what exactly is the
  Internet? The Internet is a worldwide collection
  of computer networks, cooperating with each other
  to exchange information using common standards.
  Through telephone wires, fiber optic cables,
  wireless transmissions and satellite links,
  Internet users can exchange information in a
  variety of forms.

• The Internet is a network of networks that
  connects users in every country in the world.
  There are currently over one billion Internet
  users worldwide.

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Internet Service Providers(ISPs)

• Any home, business or organization that wants to
  connect to the Internet must use an Internet
  Service Provider (ISP). An ISP is a company that
  provides the connections and support to access
  the Internet. It can also provide additional
  services such as Email and web hosting.

• ISPs range in size from small to very large
  and differ in terms of the area they service.
  ISPs may provide limited services to a small
  geographical area or can have a wide variety of
  services and support entire countries with
  millions of customers. ISPs also differ in the
  types of connection technologies and speeds they
  offer. Examples of well known ISPs include AOL,
  EarthLink, and Roadrunner.

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The ISPs Relationship With the Internet

• Individual computers and local networks connect
  to the ISP at a Point of Presence (POP). A POP is
  the connection point between the ISP's network
  and the particular geographical region that the
  POP is servicing.
• An ISP may have many Pops depending on its size
  and the area it services. Within an ISP, a
  network of high-speed routers and switches move
  data between the various Pops. Multiple links
  interconnect the Pops to provide alternate routes
  for the data should one link fail or become
  overloaded with traffic and congested.

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• ISPs connect to other ISPs in order to send
  information beyond the boundaries of their own
  network. The Internet is made up of very
  high-speed data links that interconnect ISP Pops
  and ISPs to each other. These interconnections
  are part of the very large, high capacity network
  known as the Internet Backbone.
• Connecting to the ISP at the POP provides users
  with access to the ISP's services and the
  Internet.

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Option for connecting to the Isp

• Ps provide a variety of ways to connect to the
  Internet, depending on location and desired
  connection speed.
• In a major city there are typically more choices
  for ISPs and more connection options than in a
  rural area. For example, cable Internet access is
  only available in certain metropolitan areas
  where cable TV service is available. Remote areas
  may only have access via dial-up or satellite.
• Each Internet access technology uses a network
  access device, such as a modem, in order to
  connect to the ISP. It may be built in to your
  computer or may be provided by the ISP.

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The choice of Internet access technologies
depends on availability, cost, access device
used, media used and the speed of the connection.
Most of the technologies shown are used for
both home and small business. Leased lines are
typically used for business and large
organizations, but can be used to provide high
speed connectivity in areas where cable or DSL
are not available
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ISP Levels of Service

• Depending on the ISP and the connection
  technology, various services are available such
  as virus scanning, video on demand, and file
  storage. The contract with the ISP determines the
  type and level of services that are available.
  Most ISPs offer two different contract levels
  home service or business class service.
• Home service is normally less expensive than
  business services, and generally provides
  scaled-down services such as slower connection
  speed, reduced web space storage, and fewer email
  accounts. A typical home account may include a
  minimum of five email addresses with additional
  addresses being available for a fee.

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When data is transferred, it is either uploaded
or downloaded. Downloading refers to information
coming from the Internet to your computer, while
uploading indicates the reverse path, from your
computer to the Internet. When the download
transfer rate is different from the upload
transfer rate, it is called asymmetric. When the
transfer rate is the same in both directions, it
is called symmetric

• Asymmetric
• Most commonly used for the home.
• Download speeds are faster than upload speeds.
• Necessary for users that download significantly
  more than upload.
• Most Internet users, especially those who use
  graphics or multimedia intensive web data, need
  lots of download bandwidth.

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• Symmetric
• Most commonly used for business or individuals
  hosting servers on the Internet.
• Used when necessary to upload large amounts of
  traffic such as intensive graphics, multimedia,
  or video.
• It can carry large amounts of data in both
  directions at equal rates.

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Importance of the Internet protocol (IP)

• For hosts to communicate on the Internet, they
  must be running Internet Protocol (IP) software.
  The IP protocol is one of a group of protocols
  that are collectively referred to as TCP/IP
  (Transmission Control Protocol / Internet
  Protocol). The Internet Protocol (IP) uses
  packets to carry data

• Each IP packet must contain a valid source
  and destination IP address.
  Without valid address information, packets sent
  will not reach the destination host. Return
  packets will not make it back to the original
  source.

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• An IP packet has a header at the beginning which
  contains the source and destination IP addresses.
  It also contains control information that
  describes the packet to network devices, such as
  routers, it passes through and also helps to
  control its behavior on the network. The IP
  packet is sometimes referred to as a datagram.
• IP addresses must be unique on the Internet.
  There are organizations responsible for
  controlling the distribution of IP addresses so
  that there is no duplication. ISPs obtain blocks
  of IP addresses from a local, national or
  regional Internet registry (RIR). It is the
  responsibly of the ISPs to manage these addresses
  and assign them to end users.

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How ISPs Handle packets

• Before being sent on the Internet, messages are
  divided into packets. IP packet size is between
  64 to 1500 bytes for Ethernet networks, and
  contains mostly user data. Downloading a single 1
  MB song would require over 600 packets of 1500
  bytes. Each individual packet must have a source
  and destination IP address.
• When a packet is sent across the Internet, the
  ISP determines whether the packet is destined for
  a local service located on the ISP network, or a
  remote service located on a different network.
• Every ISP has a control facility for their
  network, known as the Network Operations Center
  (NOC). The NOC usually controls traffic flow and
  houses services such as email and web hosting

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Internet Cloud

• A diagram that shows all network devices and
  their interconnections would be very complex.
  Additionally, the final routing path between
  source and destination is not usually important,
  only that the source is able to communicate with
  the destination. Therefore, in network diagrams a
  cloud is often used to represent the Internet or
  any other complex network,

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Device in Internet Cloud

• Devices that provide connectivity to end-users
  must match the technology used by the end-user to
  connect to the ISP. For example, if the end-user
  is using DSL technology to connect, the ISP must
  have a DSL Access Multiplexer (DSLAM) to accept
  these connections. For cable modems to connect,
  the ISP must have a Cable Modem Termination
  System (CMTS). Some ISPs still accept analog
  calls through modems and have banks of modems to
  support these users. ISPs that provide wireless
  access have wireless bridging equipment.

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Common Network Cables
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Twisted Pair Cables
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Coaxial Cable
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Fiber Optic Cables
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Cabling Standards

• Cabling standards are a set of specifications for
  the installation and testing of cables. Standards
  specify types of cables to use in specific
  environments, conductor materials, pinouts, wire
  sizes, shielding, cable lengths, connector types
  and performance limits.

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UTP Cables

• Twisted pair cable is most commonly used in
  network installations. The TIA/EIA organization
  defines two different patterns, or wiring scheme,
  called T568A and T568B. Each wiring scheme
  defines the pinout, or order of wire connections,
  on the end of the cable.

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Identify and describe the cross-over and straight
through cable pinouts and color codes
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UTP Cable Termination

• UTP and STP cable is usually terminated into an
  RJ-45 connector

The RJ-45 jack has eight conductors, and is wired
according to either T568A or T568B. At the patch
panel a device known as a punchdown tool is
required to push the wires into the connector.
The wires should be matched up to the appropriate
insulation displacement connector (IDC) by color
before punching them down. The punchdown tool
also cuts off any excess wire. A punchdown tool
is not required to terminate most wall jacks. To
terminate these connectors the cables are
untwisted and placed into the appropriate IDC.
Placing the cap on the jack pushes the cables
into the IDC and cuts through the insulation on
the wires.
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Describe how to test cable termination and
functionality (Cable testing).
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Describe how to test cable termination and
functionality (Cable testing).

• The cable tester is used to perform initial
  diagnostics. The first test usually is called a
  continuity test and it verifies that there is
  end-to-end connectivity. It can also detect
  common cabling faults such as opens and shorts.

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Attenuation, also commonly referred to as
insertion loss, is a general term that refers to
the reduction in the strength of a signal.
Attenuation is a natural consequence of signal
transmission over any medium. Attenuation limits
the length of network cabling over which a
message can be sent.

• Crosstalk is the leakage of signals between
  pairs. If this is measured near the transmitting
  end it is termed near-end crosstalk (NEXT). If
  measured at the receiving end of the cable it is
  termed far-end crosstalk (FEXT). Both forms of
  crosstalk degrade network performance and are
  often caused by untwisting too much cable when
  terminating.

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Summary

• The Internet is a worldwide collection of
  computer networks, accessed through ISPs.
• Internet Protocol (IP) controls the structure and
  addressing of data packets for transport through
  the Internet cloud.
• ISP Network Operations Centers (NOCs) utilize
  high-end, high-speed devices with redundancy.
• Home networks feature multi-function devices
  which perform switching and routing.
• Networks use physical cabling media which must
  conform to standards in construction and
  termination.
• Cabling best practices are designed to reduce
  attenuation and crosstalk.

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