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Ethernet Frames

Ethernet Frames. Ethernet II frame format DIX IEEE 802.3 Frame Takes an 802.2 (LLC)frame. IEEE 802.3 Frames. Ethernet Frames. IEEE 802.2 Frame Logic link control – part HDLC functions Any logical addressing Control information Data encapsulation Common to all 802 MAC protocols.

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Ethernet Frames

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  1. Ethernet Frames • Ethernet II frame format • DIX • IEEE 802.3 Frame • Takes an 802.2 (LLC)frame

  2. IEEE 802.3 Frames

  3. Ethernet Frames • IEEE 802.2 Frame • Logic link control – part HDLC functions • Any logical addressing • Control information • Data encapsulation • Common to all 802 MAC protocols

  4. Ethernet Frames • IEEE 802.2 Frame - LLC • DSAP – Destination Service Access Point • Identifies protocol stack on the receiving sys • 1 byte – 1st bit • 0- individual • 1 group

  5. Ethernet Frames • IEEE 802.2 Frame - LLC • SSAP – Source Service Access Point • Identifies protocol stack on the sending sys • 1 byte – 1st bit • 0- command • 1 - response

  6. Ethernet Frames • IEEE 802.2 Frame - LLC • Control field • I frame – information • S frame – supervisory • U frame – unnumbered frame

  7. 100Base standards • 802.3u task force – 100Mbps, same Ethernet MAC – use CAT5 • 802.12 - Demand Priority Access Method • Use CAT3 • Both accepted officially June 1995 • 802.3u popular – 100BaseT or Fast Ethernet

  8. 100 Base T • 10 Base T collision domain • 2500 mts at 10 Mbps • Collision sensing time = 512 bit period • Smallest frame size • 100 Base T – collision domain?

  9. 100 Base T • 100 Base T – features • No change in the frame format • No change in the access method – full duplex • Access rate changed • Collision domain changed • Data rate greater 10 times, collision decreased by 10 times

  10. 100 Base T – physical layer • Star topology • Two Specs • 100Base X – PCS – PMA – 2 cables • 100 Base T4 – • Four UTP cables – CAT3 – voice grade • To get reduced baud rate for a given bit rate 8B/6T encoding was used (10Base T used 4B/5B encoding)

  11. 10 Base T – > 100 Base T • 802.3u committee specifications • Seamless integration with installed base • Order of two times the 10BaseT cost (or less) • Increased aggregate bandwidth • Be standardized and supported by multiple vendors • Solution to time bound delivery

  12. 100 Base T • Auto – negotiation • Speed adjustment among devices • Allows negotiation on optimal mode between systems • Half duplex (csma/cd) • Full duplex • RS, MII, auto negotiation - Full duplex aware

  13. Flow control • Special MAC frame – PAUSE • Turn-off the transmitter • Suitable only on point-to-point links between transmitting and receiving stations • Pause ‘Time’ information sent • End of timer – transmitter can start sending

  14. PAUSE Frame • DA – globally unique – 01-80-c2-00-00-01 • Type field –88-08 • 2 byte timer field – in 512 bit times • Full duplex – derivative of switched Ethernet • Distance limitation due to collision domain removed

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