Switching Concepts

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Switching Concepts

• Module 4 Review

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4.1.1 Ethernet/802.3 LAN Development

• A hub is a Layer 1 device and is sometimes
  referred to as an Ethernet concentrator or a
  multi-port repeater.
• A hub does not make any decisions when receiving
  data signals it only amplifies the data signals
  that it receives and distributes it through all
  ports.
• Bandwidth is shared among all connected users.

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4.1.1 Ethernet/802.3 LAN Development

• Layer 2 devices are more intelligent than Layer 1
  devices.
• Layer 2 devices make forwarding decisions based
  on Media Access Control (MAC) physical addresses
  contained within the headers of transmitted data
  frames.
• Bridge
• Switch

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4.1.4 Half-duplex Networks

• As more hosts are added to the network and begin
  transmitting, collisions, and jam signals
  increase. Throughput decreases.

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4.1.4 Half-duplex Networks

• When a collision occurs, the host that first
  detects the collision will send out a jam signal
  to the other hosts. Upon receiving the jam
  signal, each host will stop sending data, then
  wait for a random period of time before
  attempting to retransmit. The back-off algorithm
  generates this random delay.

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4.1.9 Full-duplex Transmitting

• Full-duplex Ethernet offers 100 of the bandwidth
  in both directions.
• This produces a potential 20 Mbps throughput,
  which results from 10 Mbps TX and 10 Mbps RX.

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4.2.2 LAN Segmentation with Bridges

• The bridge must examine the destination address
  field and calculate the cyclic redundancy check
  (CRC) in the frame check sequence field before
  forwarding the frame.
• Bridge handling of packets
• The source MAC address and input interface pair
  are added to the Bridging Table
• If no match to the destination MAC address is
  found in the Bridging Table, the frame is flooded
  out all other interfaces.
• If a match to the destination MAC address is
  found in the Bridging Table, the frame is flooded
  out the associated interfaces.

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4.2.3 LAN Segmentation with Routers

• Routers segment broadcast domains.
• Forward packets based on the destination network
  layer address.
• Segment collision domains.

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4.2.4 LAN Segmentation with Switches

• LAN switching decreases bandwidth shortages and
  network bottlenecks, such as those between
  several workstations and a remote file server.
• A switch will segment a LAN into microsegments
  which decreases the size of collision domains.
• However all hosts connected to the switch are
  still in the same broadcast domain.
• Switches are faster than bridges because the
  switching occurs in the hardware.

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4.2.5 Basic Operations of a Switch

• Switching is a technology that decreases
  congestion in Ethernet 10Base-T, Token Ring, and
  Fiber Distributed Data Interface (FDDI) LANs.
• Latency is the period of time from when the
  beginning of a frame enters to when the end of
  the frame exits the switch

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4.2.7 Layer 2 and Layer 3 Switching

• Layer 2 switching looks at a destination MAC
  address in the frame header. The source MAC
  address is used to build the switching table.
• The switching table is contained in Content
  Addressable Memory (CAM).

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4.2.8 Symmetric and Asymmetric Switching

• Asymmetric switching enables high bandwidth to be
  dedicated to the server switch port in order to
  prevent a bottleneck.
• Memory buffering is required on an asymmetric
  switch.
• The use of buffers keeps the frames contiguous
  between different data rate ports.
• An asymmetric LAN switch provides switched
  connections between ports of unlike bandwidth,
  such as a combination of 10 Mbps and 100 Mbps
  ports.

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4.2.9 Memory Buffering

• Shared memory buffering deposits all frames into
  a common memory buffer which all the ports on the
  switch share.
• This allows the packet to be received on one port
  and then transmitted on another port, without
  moving it to a different queue.

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4.2.10 Two Switching Methods

• Fast-forward  Fast-forward switching offers the
  lowest level of latency. This is used by Bridges

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4.3.1 Functions of Ethernet Switches

• The CSMA/CD access method prevents multiple users
  on an Ethernet network from transmitting at the
  same time.

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4.3.2 Frame Transmission Modes

• The hybrid mode is called adaptive cut-through.
  In this mode, the switch uses cut-through until
  it detects a given number of errors. Once the
  error threshold is reached, the switch changes to
  store-and-forward mode.

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4.3.2 Frame Transmission Modes
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4.3.9 Switches and Broadcast Domains

• A MAC address of all ones is FFFFFFFFFFFF in
  hexadecimal.