Saturday, December 18, 2010

Ethernet Tutorial 1

One Ethernet tutorial I like very much is from Fujisu since it includes all the basics of Ethernet technologies.  The following is my reading note, and you could read the original article by clicking here. You could also
check this link from England.
  1. Ethernet History
  2. Robert Metcalfe from Xerox described his invention Ethernet in 1973. He modeled Ethernet after the Aloha network developed at University of Hawaii in the 1960s and the initial Ethernet systems ran at 2.94Mb/s. Ethernet patent was awarded to Metcalfe and his co-workers, but wholly-owned by Xerox.
  3. Ethernet Standards
  4. In 1980, DEC, Intel and Xerox (DIX) issued a DIX Ethernet standard for 10Mb/s Ethernet systems.  In 1985, IEEE  published the open Ethernet standard IEEE 802.3. Why 802? It is because work started in February 1980. For all the later Ethernet standard,  people could refer Wikipedia link 802.3 .
  5.  Ethernet Technologies
  • Fast Ethernet 
         In 1995, IEEE 802.3u defines 100Mb/s Ethernet over wire or fiber-optic cable. Speed could be auto-negotiated between equipments to choose 10Mb/s or 100Mb/s.

  • Gigabit Ethernet  
       Gigabit Ethernet uses same IEEE 802.3 frame format, full duplex and flow control methods. In addition, it supports half-duplex via CSMA/CD and SNMP tools. What's more, it introduces jumbo frames (64 ~ 9216 bytes) to reduce frame rates compared to standard frames (64 ~ 1518 bytes).
      Gigabit Ethernet could be transmit over CAT 5 cable or optical fibre such as 1000Base-CX(Copper),  1000 Base-SX(850nm fibre), and 1000Base-LX(1310nm fibre).
  • 10 Gigabit Ethernet 
        10 Gigabit Ethernet is transmitted over multi mode and single mode optical fibre in full-duplex mode, which eliminates the need for CSMA/CD. 10 Gigabit Ethernet defines 2 physical layers: LAN PHY and WAN PHY.
       2 versions of LAN PHY are standardized: 10GBase-R and 10GBase-X. 10GBase-R uses a 64B/66B encoding scheme to raise the line rate to 10.313Gb/s; While 10GBase-X still uses 8B/10B encoding  and takes advantage of  4-channel CWDM to support 10Gb/s.
      In addition to PCS, PMA and PMD in LAN PHY, WAN PHY adds WAN interface sublayer (WIS) to support SONET line rate at 9.95328 Gb/s.
      10 Gigabit Ethernet has 7 interfaces:
      10GBase-SR-LAN-850nm, 10GBase-LR-LAN-1310nm, 10GBase-ER-LAN-1550nm, 10GBase-LX4-LAN-4X1310nm, 10GBase-SW-WAN-850nm, 10GBase-LW-WAN-1310nm and 10GBase-EW-WAN-1550nm.
  • LAN/WAN PHY Sublayers
         3 sublayers exist in LAN/WAN PHY: Physical coding sublayer, Physical medium attachment and Physical medium dependent.
        The PCS encodes and decodes data streams between the MAC and PHY layer. 3 categories of PCS are 10GBASE-R(64B/66B, 10.3 Gb/s, not SONET compatible), 10GBASE-X(8B/10B, WDM) and 10GBASE-W(64B/66B, 10 Gb/s, SONET compatible).
       PMA is an optional interface. 2 PMD interfaces are XAUI and XSBI. XAUI supports 4 SERDES transmit and 4 SERDES receive for 8B/10B encoding while XSBI requires more power and more pins.
       PMD is used to meet distance objective. 4 different PMD are defined: 850nm serial, up to 65 meters;
1310 nm serial, upto 10 km, 1550 nm serial, upto 40 km, 1310 nm CWDM, upto 300 meters

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