Ethernet 802'3 Physical Layer

1
Ethernet 802.3 Physical Layer

• Topology Order in which stations receive bits
• Ethernet hubs use a bus topology
• Signal is broadcast
• All stations receive almost simultaneously

2
Ethernet 802.3 Physical Layer

• Topology Order in which stations receive bits
• Early Ethernet standards arranged stations in a
  daisy chain
• Stations broadcast on the chain in both
  directions
• All stations receive almost simultaneously
• Original idea of bus

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Ethernet 802.3 Physical Layer

• Topology Order in which stations receive bits
• Ethernet switches use a switched topology
• Signal only goes to one station

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Ethernet 802.3 Physical Layer

• Ethernet began as a bus network
• Some question whether Ethernet switching is
  really Ethernet
• However, hubs will be disappearing in the next
  few years, and almost all Ethernet will be
  switched

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Ethernet 802.3 Physical Layer

• Recent Ethernet 802.3 Standards use Unshielded
  Twisted Pair (UTP) Wiring or Optical Fiber
• For Small LANs with a Single Hub or Switch, use
  UTP Exclusively

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Physical Layer 802.3 UTP Standards

• Ethernet 802.3 10Base-T
• Physical layer standard
• Created by the 802.3 Working Group
• 10 Mbps
• Baseband transmission
• Insert signal directly into wire
• No channels
• T means uses UTP twisted-pair wire

802.3
10 Mbps
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Physical Layer 802.3 UTP Standards

• Ethernet 802.3 100Base-TX
• 100 Mbps
• 100Base-TX Not just 100Base-T because other
  100Mbps UTP standards were created but were not
  used significantly
• Ethernet 802.3 1000Base-T
• Gigabit Ethernet
• Overkill for small LANs

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Physical Layer 802.3 UTP Standards

• Wiring
• Unshielded Twisted Pair
• Bundle of 4 pairs (only uses 2 pairs)
• One pair to send
• One pair to receive
• Terminates in RJ-45 connector
• Slightly larger than RJ-11 home phone connector

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Physical Layer 802.3 UTP Standards

• Categories of UTP Wiring
• Wiring Quality, Category 3 being lowest
• For 10Base-T
• Categories 3, 4, or 5 are OK
• However, most installed wiring is Cat 5
• For 100Base-TX, Cat 5 is required
• For Gigabit Ethernet, Enhanced Category 5 is
  recommended, although Cat 5 should work if
  perfectly installed

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Physical Layer 802.3 UTP Standards

• Wiring
• 100 meters maximum UTP distance hub-to-station or
  hub-switch
• 200 meters maximum distance between stations

200 m
100 m
100 m
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Physical Layer 802.3 Standards

• NIC-Hub Communication
• NIC transmits on one pair (Pins 12)
• Hub or switch transmits on another pair (Pins 3
  6)
• Other 4 wires are not used

To Hub or Switch (Pins 12)
From Hub or Switch (Pins 36)
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Physical Layer 802.3 Standards

• Upgrading from 10Base-T to 100Base-TX
• Need new hub or switch
• May have autosensing 10/100 ports that handle
  either 10 Mbps or 100 Mbps NICs
• Need new NICs
• Only for stations that need more speed
• No need to rewire
• This would be expensive