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Thin Ethernet (10B2 / IEEE 802.3a). Segment length < 185m and > 0.5 m Up to 30 attached nodes Cable flexible and cheap Integrated or external transceiver connected via a BNC 'T' connector Used mainly for workgroups Difficult to manage (i.e. breaks in cable difficult to locate).

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thin ethernet 10b2 ieee 802 3a
Thin Ethernet (10B2 / IEEE 802.3a)
  • Segment length < 185m and > 0.5 m
  • Up to 30 attached nodes
  • Cable flexible and cheap
  • Integrated or external transceiver connected via a BNC 'T' connector
  • Used mainly for workgroups
  • Difficult to manage (i.e. breaks in cable difficult to locate)
10bt 802 3i
10BT/802.3i
  • Connects the computer directly (i.e. using a point to point link) to a wiring hub.
  • Segment length 100 m
  • Cable flexible and very cheap
  • Standard RJ-45 connector used (also can be used for telephone and other networks)
  • Used mainly for work groups (requires a hub to connect to the LAN)
  • Easy to manage (also can be used for telephone and other networks)
ethernet repeaters and hub
Ethernet Repeaters and Hub
  • operate at the Physical Layer
  • connect together one or more Ethernet cable segments to provide signal amplification and regeneration
  • A network of repeaters and hubs is therefore called a "Shared Ethernet" or a "Collision Domain".
  • Only one host is allowed to transmission within a Collision Domain

An 3Com Office Hub (8 ports)

  • No (or little) processing (memory) unit
  • all ports operate as one Ethernet LAN
  • all connected NICs operate in the half-duplex (CSMA/CD) mode at the same transmission speed

Stack of several hubs to wire a building

ethernet bridges switches
Ethernet Bridges & Switches
  • bridge has to forward frames from one LAN to another
  • Operates at the data link layer
  • Bridges Must learn which addresses belong to the computers connected via each port.
  • Separate Collision Domain
ethernet switches
Ethernet Switches
  • Solution to put 300 hosts in one Ethernet (in one building)
  • Separate the Collision domain
  • Contain a high-speed backplane
  • Store-and-forward (inboard memory for each line)
  • ranging from the simplest low cost devices
  • to expensive high performance switches

3Com LinkSwitch

1000

Cisco Catalyst 5000 Switch

frame format
Frame Format
  • A sent at t0
  • B send around t0+
  • B realize collision and send noise burst
  • A hear the noise burst at around t0+ 2
  • A must not conclude transmission success before t0+2
  • Preamble
  • Dest Addr: 6-byte MAC address
  • Source Addr: 6-byte MAC address
  • Length: 1500 bytes maximum
  • Data
  • Pad: minimum 64 bytes
    • To distinguish valid fames and garbage
    • Transmission should last longer than round-trip delay.
  • Checksum
round trip delay and transmission time
Round-trip Delay and Transmission Time
  • With maximum length 2500 meters
  • Four repeaters
  • Round-trip time: 50 usec
  • At 10 Mbps, one bit last 100 nsec
  • Thus 500 bits are needed to last 50 usec
  • Which is roughly 64 bytes
binary exponential backoff
Binary Exponential Backoff
  • How stations randomly wait after a collision
    • One slot is 51.2 usec (round-trip delay)
    • At first collision, each station waits 0 or 1 slots
    • After the second collision, each station waits either 0, 1, 2, or 3 slots randomly.
    • If a third collision occurs, wait 0 to 7 slots.
    • So on and so forth
    • Maximum slots to wait is 1023 after 16 straight collisions
fast ethernet and gigabit ethernet
Fast Ethernet and Gigabit Ethernet
  • 100 Base-T4
  • 100 Base-TX
  • All gigabit Ethernet is point-to-point
  • Full-duplex mode
    • Must use switch (not hub!)
    • No contention
    • No need for media sensing
  • Half-Duplex mode
    • Connected with Hub
    • Collision is possible