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ORIGINS AND HISTORY OF ETHERNET

• Pre-1976 - Xerox was interested in finding a way to share their expensive printers between workstations
• 1976 - Dr. Robert Metcalf (also David Boggs?) at PARC was tasked with creating a shared communications mechanism for this purpose. Dr. Metcalfe wrote a paper circa called "Ethernet Distributed Packet Switching for Local Computer Networks"
• 1973 - Dr. Metcalfe aquired patent #4,063,220 for his Ethernet.
• Ethernet was originally called the Alto Aloha Network protocol or "ALOHAnet" (later renamed Ethernet to indicate multi-platform compatibility)
• 1979 - DEC and Intel joined forces with Xerox write a standard for ethernet. This was referred to as the DIX standard, and the publication was called the Ethernet Bluebook. Ethernet is defined as a 10 Mbps protocol running over coaxial cable and using CSMA/CD for transmission (thicknet).
• 1983 - The IEEE released their version of the Ethernet standard in in the document IEEE 802.3. IEEE 802.3 was based largely on the DIX standard but with significant changes in frame format. However it was still backwards compatible with the DIX standard.
• 1985 - IEEE 802.3a "Thinnet" (10 Mbps) - lower cost than thicknet.
• 1987 - IEEE 802.3d "FOIRL" - Fibe Optic Inter-Repeater Link (10Mbps at 1000 meters)
• 1990 - IEEE 802.3i - "10bT" - Category 3 Unshielded Twisted pair compatible cabling. Allowed use of existing telephony wiring.
• 1993 - IEEE 802.3j - 10bF - 2000' range over fiber
• 1995 - IEEE 802.3u - Defines the modern-day 100bT standard.
• 1997 - IEEE 802.3x - Full duplex operation

DESCRIPTION

• Digital packetized broadcast communication on shared medium (bus) - 2.74 Mbps (clock speed of Alto computers) was original speed, later 10, 100 and 1000 Mbps.
• ~3 & 10 Mbps - uses Manchester encoding (manchester prevents baseline wander through bandpass filter)
• 100 Mbps
  • Three standards
    • 100Base-TX
    • 100Base-T4
    • 100Base-T2
• 1000 - Uses Forward Error Correction
• Utilizes Manchester signaling in 3 mbps and 10 mbps over UTP (other protocols in 100 and 10000)
  • AC coupled to tranceivers - No DC source required
  • Manchester prevents baseband wander
  • Encodes clock and data in same signal (thus the need for the preamble)
  • Difference between two described methods of producing manchester signal (Stallings vs. Tananbaum)
  • OSI relationship (Cisco)
    • Data Link
      • LLC
      • MAC
    • Physical
      • Media independant
        • Reconcilliation
        • Media-Independant Interface (optional) - 10,100; GMII in GigE
      • Media dependant
        • Physical coding sublayer
        • Physical Medium Attachment
        • Auto-negotiation (optional in 3 & 10, mandatory in later 100 and in 1000)
• Collision detection mechanism - (Two transmitting stations raise voltage above threshold - thus, collision)