CCNA 1 v3.0 Module 6 Ethernet Fundamentals

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CCNA 1 v3.0 Module 6Ethernet Fundamentals
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Objectives
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Introduction to Ethernet

• Ethernet is not one technology but a family of
  LAN technologies and may be best understood by
  using the OSI reference model.

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IEEE Ethernet Naming Rules
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Ethernet and the OSI Model
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The success of Ethernet is due to the following
factors

• Simplicity and ease of maintenance
• Ability to incorporate new technologies
• Reliability
• Low cost of installation and upgrade

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Ethernet and the OSI Model
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Ethernet and the OSI Model
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Ethernet and the OSI Model
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Ethernet and the OSI Model
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Naming
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• A system called Alohanet was developed to allow
  various stations on the Hawaiian Islands
  structured access to the shared radio frequency
  band in the atmosphere.  This work later formed
  the basis for the Ethernet access method known as
  CSMA/CD.

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Naming
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• Ethernet standard were sold during the early
  1980s. Ethernet transmitted at up to 10 Mbps over
  thick coaxial cable up to a distance of two
  kilometers. This type of coaxial cable was
  referred to as thicknet

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• Ethernet relies on baseband signaling, which uses
  the entire bandwidth of the transmission medium.
  The data signal is transmitted directly over the
  transmission medium. In broadband signaling, not
  used by Ethernet, the data signal is never placed
  directly on the transmission medium. An analog
  signal (carrier signal) is modulated by the data
  signal and the modulated carrier signal is
  transmitted. Radio broadcasts and cable TV use
  broadband signaling.

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Layer 2 Framing
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Ethernet Frame

• A voltage vs. time graph could be used to
  visualize bits. However, when dealing with larger
  units of data, addressing and control
  information, a voltage vs. time graph could
  become large and confusing. Another type of
  diagram that could be used is the frame format
  diagram,

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Layer 2 Framing
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Ethernet Frame Structures
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Ethernet Frame Structures
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Ethernet Frame Structures
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• Most frames have some specialized fields. In some
  technologies, a length field specifies the exact
  length of a frame in bytes. Some frames have a
  type field, which specifies the Layer 3 protocol
  making the sending request.

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Ethernet Frame Fields
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Ethernet Frame Fields
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• MAC refers to protocols that determine which
  computer on a shared-medium environment, or
  collision domain, is allowed to transmit the
  data. MAC, with LLC, comprises the IEEE version
  of the OSI Layer 2. MAC and LLC are sublayers of
  Layer 2. There are two broad categories of Media
  Access Control, deterministic (taking turns) and
  non-deterministic (first come, first served).

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Media Access Control (MAC)
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• Non-deterministic MAC protocols use a first-come,
  first-served approach. CSMA/CD is a simple
  system. The NIC listens for an absence of a
  signal on the media and starts transmitting. If
  two nodes transmit at the same time a collision
  occurs and none of the nodes are able to
  transmit.

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MAC Rules and Collision Detection/Backoff
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MAC Rules and Collision Detection/Backoff
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Ethernet Timing
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• The actual calculated slot time is just longer
  than the theoretical amount of time required to
  travel between the furthest points of the
  collision domain, collide with another
  transmission at the last possible instant, and
  then have the collision fragments return to the
  sending station and be detected.

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Interframe Spacing and Backoff
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• The minimum spacing between two non-colliding
  frames is also called the interframe spacing.
  This is measured from the last bit of the FCS
  field of the first frame to the first bit of the
  preamble of the second frame.

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Interframe Spacing and Backoff
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Error Handling
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Types of Collisions
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Types of Collisions
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Ethernet Errors
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Ethernet Errors
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FCS Errors
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FCS

• There are three primary ways to calculate the
  Frame Check Sequence number
• Cyclic Redundancy Check (CRC) performs
  calculations on the data.
• Two-dimensional parity adds an 8th bit that
  makes an 8 bit sequence have an odd or even
  number of binary 1s.
• Internet checksum adds the values of all of the
  data bits to arrive at a sum.

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Ethernet Auto-Negotiation
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Ethernet Auto-Negotiation
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Transmission Priority Rank
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Summary