Wired LAN Technology (Ethernet and 802.3)

The Ethernet The first Ethernet was tested in – Invented by Robert Metcalfe in Xerox – Competitive technology: token ring by IBM – DIX (Digital Equipment Corporation, Intel, Xerox) coalition against IBM

Ethernet, DEC, Xerox DEC(Digital Equipment Corporation) – A major computer manufacturer in 1960s s – ranked among the most profitable companies in the USA in late 80s boasted that it never had a general layoff predicted that the PC will fall flat on its face in business – DEC  Compaq (1998)  HP(2002) Xerox – The birthplace of WIMP (Window, Icon, Menu, and Pointing device), desktop computing, digital printing, and many more – frowned upon by the then board of directors, who ordered the Xerox engineers to share them with Apple and, later, Microsoft

Ethernet, Metcalfe Robert Metcalfe – Metcalfe's law, also known as network effects The value of a network is proportional to the square of the number of its connected members. – He made some wrong predications about the Internet. Internet collapse in 1996 Linux would be obliterated after Microsoft released Windows 2000 Wi-Fi would die out in the mid 1990s

Ethernet, Metcalfe During his keynote speech at the sixth International World Wide Web Conference in 1997, he took a printed copy of his column that predicted the collapse, put it in a blender with some liquid and then consumed the pulpy mass.

Ethernet Frame Format An Ethernet frame consists of – a fixed-length header – a variable-length payload – a fixed-length CRC (Cyclic Redundancy Check)

Ethernet Type Field

Ethernet Evolution The original Ethernet – Thick wire Ethernet or Thicknet – The medium consisted of a heavy coaxial cable – 10Base5 10: bit rate (10 Mbps). 5: the maximum length of a network segment (500 meters)

Thicknet Wiring An NIC handles the digital aspects of communication. – Address recognition, CRC computing, etc. A transceiver connected to the Ethernet cable – Carrier detection, analog signals / bits conversion, etc. A physical cable known as an Attachment Unit Interface (AUI) connected a transceiver to a NIC in a computer transceiver

Review: Bus Topology in Detail 1.P-A will compose the packet 2.P-A forwards the packet to NIC-A 3.NIC-A calculates the CRC, adds SOH, EOT 4.NIC-A modulates the packet  send out 5.After a while, NIC-C will receive the m-carrier 6.NIC-C demodulates the packet and put it into its cache 7.NIC-C does address checking; if the packet is not for P-C, discard it 8.NIC-C does length and CRC checkings; If failed, the packet will be discarded 9.If the packet passes all checkings, NIC-C will strip off SOH, EOT, CRC, and send “|C|A|I like you|” to P-C Steps for P-A to send “I like you” to P-C: CRCI like youSOHEOTCAI like you C A

Review: The Collision Problem Advanced solution: CSMA/CD (CD = Collisions Detection) 1.During the whole transmission period of any packet (after it is send out) the sender keeps on sensing the bus. 2.If any other m-carrier is sensed, stop transmitting instantly; wait for a random amount of time; then retransmit

Thinnet Wiring A second generation of Ethernet Thinner coaxial cable: – 10Base2 Segment length: 200 meters. Thinnet integrates a transceiver directly on the NIC – Runs a coaxial cable from one computer to another

Thinnet Ethernet Wiring Advantages – Lower overall cost and ease of installation No need for external transceivers & AUI cables Disadvantage?

Twisted Pair Ethernet Wiring and Hubs A third generation of Ethernet – Uses a hub separate from the computers attached to the network – Shielded cabling: twisted-pair wires. – 10BaseT T: Twisted pair Segment length: 100 meters.

Hub A hub emulates a physical cable – Making the entire system operate like a conventional Ethernet – A system that attached to a hub uses CSMA/CD to access the network

What’s the Topology of Twisted Pair Ethernet? v.s. HubSwitch

Wiring in an Office Building The type of wiring makes a major difference in a large building.

Variants of Twisted Pair Ethernet and Speeds The data rate used on twisted pair Ethernet has increased Higher-speed Ethernet technologies use switches rather than hubs.