Ethernet

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Ethernet

• Kenneth Castelino

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Network Architecture - Protocols

• Physical Actual signal transmission
• Data-Link Framing / Error Detection
• Network Routing / Addressing
• Transport Congestion / Flow Control
• Application Specific to user needs

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Layered Protocols (HTTP)
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Data Link Layer - Ethernet

• Invented in 1973 _at_ Xerox. (IEEE 802.3)
• Originally a LAN technology extended to MAN /
  WAN.
• Same frame format, different wiring schemes, data
  rates across generations.
• Most common version (10BaseT) 1990.

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Ethernet Generations

• Original Ethernet
• Coaxial cable (10Base5)
• Thicknet.
• Next Generation
• Thin coax cable (10Base2)
• Thinnet.
• Modern Ethernet
• Twisted pair ethernet (10BaseT)
• Uses hub physical star but logical bus.

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Ethernet Components

• NIC Network Interface Card
• Integrated Tx/Rx direct interface to medium.
• MAU Media Attachment Unit
• Attaches network interface to the medium
  (integrated into NIC).
• AUI Attachment Unit Interface
• Decouple physical layer -reuse MAC design with
  different media.
• MII Media Independent Interface
• Like AUI for gigabit / faster ethernets.

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Ethernet Addressing

• 48-bit address
• Address assigned when NIC card is manufactured.
• Packets can be sent to
• Single address Unicast
• All stations on network Broadcast (address
  all 1s.)
• Subset of stations Multicast
• Broadcast (address all 1s.)
• All receivers accepts unicast / broadcats.
• Half addresses reserved for multicast (247)
• NIC can accepts zero or more multicasts.

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Ethernet Frame

• Sender adds
• Senders address is source
• Recepients addreess in destination
• Type of data in frame type
• Error check data (CRC)
• Receiver NIC
• Gets transmitted frame.
• Examines address and either accepts or rejects.
• Passes frame to system software.

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Media Access Control - MAC

• Shared medium stations take turns at sharing
  the medium.
• Media access control ensures fairness.
• CSMA / CD
• Carrier Sense wait till medium is idle before
  sending frame.
• Multiple Access multiple computers use the same
  shared media. Each uses same access algorithm.
• Collision Detection Listen to medium detect if
  another stations signal interferes back off
  and try again later.

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CSMA / CD

• If collision occurs wait a random time t1 - 0lt
  t1ltd.
• D depends on transmission speed time for frame
  width or 512 bits.
• If second collision occurs, wait a random time t2
  - 0lt t2lt2d.
• Double range for each succesive collision.
• Exponential backoff
• No acknowledgement like TCP.
• CSMA/CA used in wireless networks where not all
  stations receive message.
• Both sides send small message followed by data
• X is about to send to Y
• Y is about to receive from X
• Data frame sent from X to Y.

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Recent Developments

• 100Base-FX
• LED light source / MMF / 2 km max distance.
• Modal dispersion limited bandwidth
• 100Base-SX (IEEE 802.3z)
• Short wavelength laser (850 nm)
• Max distance 5 km.
• 100Base-LX
• Long wavelength laser (1310 nm)
• Max distance 5 km.

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Beyond Gigabit Ethernet

• 10 Gb/s Ethernet
• No CSMS/CD, same frame format.
• Applications
• Upgrade LANs / Backbone.
• MAN applications.

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References

• 1 I.P. Kaminow, Tingye Li, Ed., Optical Fiber
  Telecommunications IV, Chapter 11, Academic
  Press, 2002.
• 2 John Chuang, SIMS 250 , UC Berkeley, Fall
  2001.