ICS 31: COMPUTER NETWORKS and DATA COMMUNICATION

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ICS 31 COMPUTER NETWORKS and DATA COMMUNICATION

• The Teaching Topology

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TOPOLOGY

• The structure of the network
• 2 PARTS
• PHYSICAL TOPOLOGY
• The actual layout of the wire (media)
• LOGICAL TOPOLOGY
• defines how the media is accessed by the hosts
• how the hosts communicate across the medium

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PHYSICAL TOPOLOGIES

• A bus topology uses a single backbone segment
  (length of cable) that all the hosts connect to
  directly.
• A ring topology connects one host to the next and
  the last host to the first. This creates a
  physical ring of cable.
• A star topology connects all cables to a central
  point of concentration. This point is usually a
  hub or switch.

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PHYSICAL TOPOLOGIES

• An extended star topology uses the star topology
  to be created. It links individual stars together
  by linking the hubs/switches. This, as you will
  learn later in the chapter, will extend the
  length and size of the network.
• A hierarchical topology is created similar to an
  extended star but instead of linking the
  hubs/switches together, the system is linked to a
  computer that controls the traffic on the
  topology.

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PHYSICAL TOPOLOGIES

• A mesh topology is used when there can be
  absolutely no break in communications, for
  example the control systems of a nuclear power
  plant. This also reflects the design of the
  Internet, which has multiple paths to any one
  location. 

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LOGICAL TOPOLOGY

• Broadcast topology simply means that each host
  sends its data to all other hosts on the network
  medium. There is no order the stations follow to
  use the network, it is first come, first serve.
  This is the way that Ethernet works.

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LOGICAL TOPOLOGY

• Token-passing controls network access by passing
  an electronic token sequentially to each host.
  When a host receives the token, that means that
  that host can send data on the network. If the
  host has no data to send, it passes the token to
  the next host and the process repeats itself.

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LAN DEVICES

• Layer 1 Device
• MEDIA
• The basic functions of media are to carry a flow
  of information, in the form of bits and bytes
  through a LAN
• Other than wireless LANs (that use the
  atmosphere, or space, as the medium) networking
  media confine network signals to a wire, cable,
  or fiber
• You can build computer networks with many
  different media types. Some of the advantages and
  disadvantages are
• Cable length
• Cost
• Ease of installation

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Layer 1 Device

• Repeaters
• One of the disadvantages of the type of cable
  that we primarily use ( CAT 5 UTP) is cable
  length.
• The maximum length for UTP cable in a network is
  100 meters (approx. 333 feet). If we need to
  extend our network beyond that limit, we must add
  device to our network. This device is called a
  REPEATER.
• It also comes from telegraph, telephone,
  microwave and optical communications, all of
  which use repeaters to strengthen their signals
  over long distances, or else the signals will
  eventually fade or die out.

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REPEATERS

• The purpose of a repeater is to regenerate and
  retime network signals at the bit level to allow
  them to travel a longer distance on the media.
• The term repeater traditionally meant a single
  port in and a single port out device.
• Repeaters are classified as Layer 1 devices in
  the OSI model because they act to only on the bit
  level and look at no other information.

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Layer 1 Device

• HUB
• The purpose of a hub is to regenerate and retime
  network signals. This is done at the bit level to
  a large number of hosts (4,8,24) using a process
  known as concentration.
• You will notice that this definition is very
  similar to the repeater, which is why a hub is
  also known as a multi-port repeater. The
  difference is the number of cables that connect
  to the device.

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HUB

• Two reasons for using HUBS
• To create a central connection point for the
  wiring media
• Increase the reliability of the network
• The reliability of the network is increased by
  allowing any single cable to fail without
  disrupting the entire network.
• Hubs are considered Layer 1 devices because they
  only regenerate the signal and broadcast it out
  to all of their ports.

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HUBS

• Classifications
• ACTIVE
• Most modern hubs are active they take energy
  from a power supply to regenerate network signals
• PASSIVE
• It merely split the signal for multiple users,
  like using a Y cord on a CD player to use more
  than one set of headphones.
• Passive hubs do not regenerate bits, so they do
  not extend cables length, they only allow two or
  more hosts to connect to the same cable segment.
• INTELLIGENT
• Have console ports which means they can be
  programmed to manage network traffic

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HUBS

• Classifications
• DUMB HUBS
• Simply take an incoming networking signal and
  repeat it to every port without the ability to do
  any management.

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Layer 2 Device

• Bridge
• A bridge is a Layer 2 device designed to connect
  two LAN segments. The purpose of a bridge is to
  filter traffic on a LAN, to keep local traffic
  local, yet allow connectivity to other parts
  (segments) of the LAN for traffic that has been
  directed there.
• You may wonder, then, how the bridge knows which
  traffic is local and which is not. The answer is
  the same one that the postal service uses when
  asked how it knows which mail is local. It looks
  at the local address. Every networking media has
  a unique MAC address on the NIC, the bridge keep
  track of which MAC addresses are on each side of
  the bridge and makes its decisions based on this
  MAC address list.

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BRIDGE

• The term bridge refers to a device which has just
  two ports. However, you will see references to
  bridges with 3 or more ports.

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Layer 2 Device

• SWITCHES
• A layer 2 device just as a bridge is. In fact, a
  switch is called a multi-port bridge, just like a
  hub is called a multi-port repeater. The
  difference between the hub and switch is that
  switches make decisions based on MAC addresses
  and hubs dont make decisions at all.
• Because of the decisions that switches make, they
  make a LAN much more efficient. They do this by
  switching data only out the port to which the
  proper host is connected. In contrast, a hub will
  send the data out all of its ports so that all of
  the hosts have to see and process (accept or
  reject) all of the data.

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SWITCHES

• Switches at first glance often look like hubs.
  Both hubs and switches have many connection
  ports, since part of their function is
  connectivity concentration (allowing many devices
  to be connected to one point in the network). The
  difference between a hub and a switch is what
  happens inside the device.
• The purpose of a switch is to concentrate
  connectivity, making data transmission more
  efficient. For now, think of the switch as
  something that is able to combine the
  connectivity of a hub with the traffic regulation
  of a bridge on each port.

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Layer 3 Device

• Router
• The router is the first device that you will work
  with in the OSI network layer. Working at Layer 3
  allows the router to make decisions based on
  groups of network addresses (classes) as opposed
  to individual layer 2 MAC addresses. Routers can
  also connect different layer 2 technologies, such
  as Ethernet, Token-Ring and FDDI. However,
  because of their ability to route packets based
  on Layer 3 information, routers have become the
  backbone of the Internet, running IP protocol.

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Router

• The purpose of a router is to examine incoming
  packets, choose the best path for them through
  the network and switch them to the proper
  outgoing port. Router are the most important
  traffic regulating devices on large networks.
  They enable virtually any types of computer to
  communicate with any other computer anywhere in
  the world.

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Layer 1-7 device

• CLOUDS
• The cloud symbol suggest another network, perhaps
  the entire Internet. It reminds us that there is
  a way to connect to that other network (the
  Internet), but does not supply all the details of
  either the connection or the network.
• The purpose of the cloud is to represent a large
  group of details that are not pertinent to a
  situation, or description, at a given time.
• Cloud is not really a single device, but a
  collection of devices that operate at all levels
  of the OSI model.

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