Ethernet 802.3 Physical Layer

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

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

Ethernet 802.3 Physical Layer• Topology: Order in which stations receive

bits

• Ethernet switches use a switched topology– Signal only goes to one station

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

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

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

10 Mbps

802.3

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

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

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

Physical Layer: 802.3 UTP Standards

• Wiring

– 100 meters maximum UTP distance hub-to-station or hub-switch

– 200 meters maximum distance between stations

100 m 100 m

200 m

Physical Layer 802.3 Standards• NIC-Hub Communication

– NIC transmits on one pair (Pins 1&2)– Hub or switch transmits on another pair (Pins 3

& 6)– Other 4 wires are not used

To Hub or Switch (Pins 1&2)

From Hub or Switch (Pins 3&6)

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