Ethernet 802 3 Physical Layer Topology Order in

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 10 Base-T 802. 3 – 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

Physical Layer 802. 3 UTP Standards • Ethernet 802. 3 100 Base-TX – 100 Mbps – 100 Base-TX: Not just 100 Base-T because other 100 Mbps UTP standards were created but were not used significantly • Ethernet 802. 3 1000 Base-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 10 Base-T – Categories 3, 4, or 5 are OK – However, most installed wiring is Cat 5 • For 100 Base-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-tostation or hub-switch – 200 meters maximum distance between stations 200 m 100 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 10 Base-T to 100 Base-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