Ethernet Frames Ethernet II frame format DIX IEEE

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

Ethernet Frames • IEEE 802. 2 Frame - LLC – DSAP – Destination Service Access Point – Identifies protocol stack on the receiving sys – 1 byte – 1 st bit • 0 - individual • 1 group

Ethernet Frames • IEEE 802. 2 Frame - LLC – SSAP – Source Service Access Point – Identifies protocol stack on the sending sys – 1 byte – 1 st bit • 0 - command • 1 - response

Ethernet Frames • IEEE 802. 2 Frame - LLC – Control field • I frame – information • S frame – supervisory • U frame – unnumbered frame

100 Base standards • 802. 3 u task force – 100 Mbps, same Ethernet MAC – use CAT 5 • 802. 12 - Demand Priority Access Method – Use CAT 3 • Both accepted officially June 1995 • 802. 3 u popular – 100 Base. T or Fast Ethernet

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?

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

100 Base T – physical layer • Star topology • Two Specs – 100 Base X – PCS – PMA – 2 cables – 100 Base T 4 – • Four UTP cables – CAT 3 – voice grade • To get reduced baud rate for a given bit rate 8 B/6 T encoding was used (10 Base T used 4 B/5 B encoding)

10 Base T – > 100 Base T • 802. 3 u committee specifications – Seamless integration with installed base – Order of two times the 10 Base. T cost (or less) – Increased aggregate bandwidth – Be standardized and supported by multiple vendors – Solution to time bound delivery

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

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

PAUSE Frame • DA – globally unique – 01 -80 -c 2 -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