Three Reasons For Using A LAN

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Three Reasons For Using A LAN

• Reduce Hardware Cost Example?
• Reducing Software Cost.Example?
• Maximizing staff efficiencyExample?

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Dedicated vs Peer-to-peer LANs

• Draw a diagram for a dedicated LAN
• Draw a diagram for a Peer-to-Peer LAN.
• Example of dedicated LANS.
• Example of Peer-to-Peer LANS.
• Which is more powerful 1 or 2?
• Which is more difficult to manage 1 or 2?
• Which is cheaper 1 or 2?
• Which is more difficult to maintain 1 or 2?

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• Name Six Network Components
• Use above components to Draw a typical LAN
  Diagram.
• Draw a LAN without using a HUB and compare with
  using a HUB.

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HUBs

• What are HUB duties?
• What are typical Port size used in different
  HUBs?
• What type of cables are used in HUBs?
• Can a HUB deal with more than one cable type?
• Does a HUB provide Bus or Ring topology?

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Ethernet (IEEE 802.3)

• What is the most popular LAN protocol( Ethernet
  or Ring)?
• What are the Three most popular Ethernet types?
  HUB, Switched, and Wireless
• What type of cables are used in Ethernet LANs?
  ALL

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• Ethernets logical topology is a bus topology.
• This means all computers on the network receive
  messages from all other computers, whether the
  message is intended for those computers or not.
• When a frame is received by a computer, the first
  task is to read the frames destination address
  to see if the message is meant for it or not.
• Although, a decade ago most Ethernet LANs used a
  physical bus, almost all Ethernets today use a
  physical star topology, with the networks
  computers linked into hubs.
• It is also common to link use multiple hubs to
  form more complex physical topologies (Figure
  6-4).

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Ethernet Media are formatted as follows
Value1Base/BroadValue2 Value 1 Data Rate for
Medium 10 10Mbps Base or Broad Base Baseband
Mode meaning only one (digital) channel Broad
Broadband (analog) cable transmissions use more
than one channel (e.g., cable TV) Value2
(relates to maximum distance possible in hundreds
of meters or cable type T twisted pair, F fiber)
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HUB Ethernet

• Give four examples of Twisted-pair Ethernet
  cables

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Maximum Speed of Guided Ethernet LANs
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Switched Ethernet

• What is the difference in functionality between
  HUB Ethernet and Switched Ethernets?
• Functionality (N-1) nodes Listen
• 1 node
  transmit
• Advantage of Switch as compared to HUBS?

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• Switched Ethernet uses switches instead of hubs.
  
• While a hub broadcasts frames to all ports, the
  switch reads the destination address of the frame
  and only sends it to the corresponding port.
• The effect is to turn the network into a group of
  point-to-point circuits and to change the
  logical topology of the network from a bus to a
  star.

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Switch configuration

• Node-Node Star connection.
• Table starts to build as more ports are used.
• 95 transmission efficiency.
• 10Base-T switch achieves up to 95Mbps.
• 10/100 switch provides 10Mbps for the clients and
  100Mbps for the attached servers.

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Media Access ControlCarrier Sense Multiple
Access/Collision Detection

• Ethernets medium access control protocol, called
  CSMA/CD, is contention-based
• With a contention-based protocol, frames can be
  sent by two computers on the same network at the
  same time, in which case they will collide and
  become garbled.
• CSMA/CD, can thus be termed ordered chaos
  because it tolerates, rather than avoids,
  collisions caused by two computers transmitting
  at the same time.

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Main Switch Advantages

• No Collision. Why?
• No bottleneck why?

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CSMA/CD

• Stands for Carrier Sense Multiple Access w/
  Collision Detect
• Carrier Sense computers listen to the network to
  see if another computer is transmitting before
  sending anything themselves.
• Multiple Access all computers have access to the
  network medium.
• Collision Detect if they detect a collision
  (CD), they then wait a random amount of time and
  resend the frame (It has to be random in order to
  avoid another collision).

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Basic Switch Operation

• Switches make forwarding decisions based on
  forwarding tables (similar to routing tables).
• When a frame is received, the switch reads its
  data link layer destination address and sends
  the frame out the corresponding port in its
  forwarding table.
• Switches making switching decisions based on data
  link layer addresses are called layer-2 switches.
• When a switch is first turned on, its forwarding
  table is empty. It then learns which ports
  correspond to which computers by reading the
  source addresses of the incoming frames along
  with the port number that the frame arrived on.
• If the switchs forwarding table does not have
  the destination address of the frame, it
  broadcasts the frame to all ports.
• Thus, a switch starts by working like a hub and
  then works more and more as a switch as it fills
  its forwarding table.

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Wireless Ethernet (IEEE 802.11)

• Wireless LANs dispense with cables and use radio
  or infrared frequencies to transmit signals
  through the air.
• WLANs are growing in popularity because they
  eliminate cabling and facilitate network access
  from a variety of locations and for mobile
  workers (as in a hospital).
• The most common wireless networking standard is
  IEEE 802.11, often called Wireless Ethernet or
  Wireless LAN.

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Wireless LAN Topology

• WLAN topologies are the same as on Ethernet
  physical star, logical bus (Figure 6-7).
• Wireless LAN devices use the same radio
  frequencies, so they must take turns using the
  network.
• Instead of hubs, WLANs use devices called access
  points (AP). Maximum transmission range is about
  100-500 feet. Usually a set of APs are installed
  making wireless access possible in several areas
  in a building or corporate campus.
• Each WLAN computer uses an NIC that transmits
  radio signals to the AP.
• Because of the ease of access, security is a
  potential problem, so IEEE 802.11 uses 40-bit
  data encryption to prevent eavesdropping.

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Figure 6-7 A wireless Ethernet access point
connected into an Ethernet Switch.
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WLAN Media Access Control

• Wireless LANs use CSMA/CA where CA collision
  avoidance (CA). With CA, a station waits until
  another station is finished transmitting plus an
  additional random period of time before sending
  anything.
• Two different WLAN MAC techniques are now in
  use the Physical Carrier Sense Method and the
  Virtual Carrier Sense Method.

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Physical Carrier Sense Method

• In the physical carrier sense method, a node that
  wants to send first listens to make sure that the
  transmitting node has finished, then waits a
  period of time longer.
• Each frame is sent using the Stop and Wait ARQ,
  so by waiting, the listening node can detect that
  the sending node has finished and can then begin
  sending its transmission.
• With Wireless LANs, ACK/NAK signals are sent a
  short time after a frame is received, while
  stations wishing to send a frame wait a somewhat
  longer time, ensuring that no collision will
  occur.

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Virtual Carrier Sense Method

• When a computer on a Wireless LAN is near the
  transmission limits of the AP at one end and
  another computer is near the transmission limits
  at the other end of the APs range, both
  computers may be able to transmit to the AP, but
  can not detect each others signals.
• This is known as the hidden node problem. When it
  occurs, the physical carrier sense method will
  not work.
• The virtual carrier sense method solves this
  problem by having a transmitting station first
  send a request to send (RTS) signal to the AP. If
  the AP responds with a clear to send (CTS)
  signal, the computer wishing to send a frame can
  then begin transmitting.

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Types of Wireless Ethernet

• Two forms of the IEEE 802.11b standard currently
  exist
• Direct Sequence Spread Spectrum (DSSS) uses the
  entire frequency band to transmit information.
  DSSS is capable of data rates of up to 11 Mbps
  with fallback rates of 5.5, 2 and 1 Mbps. Lower
  rates are used when interference or congestion
  occurs.
• Frequency Hopping Spread Spectrum (FHSS) divides
  the frequency band into a series of channels and
  then changes its frequency channel about every
  half a second, using a pseudorandom sequence.
  FHSS is more secure, but is only capable of data
  rates of 1 or 2 Mbps.
• IEEE 802.11a is another Wireless LAN standard
  that is still being defined. It will operate in
  the 5 GHz band and be capable of data rates of up
  to 54 Mbps, but will probably average about 20
  Mbps in practice.

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Infrared Wireless LANs

• Infrared WLANs are less flexible than IEEE 802.11
  WLANs because, as with TV remote controls that
  are also infrared based, they require line of
  sight to work.
• Infrared Hubs and NICs are usually mounted in
  fixed positions to ensure they will hit their
  targets.
• The main advantage of infrared WLANs is reduced
  wiring.
• A new version, called diffuse infrared, operates
  without a direct line of sight by bouncing the
  infrared signal off of walls, but is only able to
  operate within a single room and at distances of
  only about 50-75 feet.

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Fig. 6-9 Infrared Wireless LAN
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Bluetooth

• Bluetooth is a 1 Mbps wireless standard developed
  for piconets, small personal or home networks.
• It may soon be standardized as IEEE 802.15.
• Although Bluetooth uses the same 2.4 GHz band as
  Wireless LANs it is not compatible with the IEEE
  802.11 standard and so can not be used in
  locations that use the Wireless LANs.
• Bluetooths controlled MAC technique uses a
  master device that polls up to 8 slave devices.
• Examples of Bluetooth applications include
  linking a wireless mouse, a telephone headset, or
  a Palm handheld computer to a home network.

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