Ethernet Manchester Encoding 0 85 0 -85 1us Positive transition for o, negative for 1 Transition every cycle communicates clock (but need 2 transition times per bit) DC balance has good electrical properties ecture 6 15441@2008 11
Ethernet Manchester Encoding •Positive transition for 0, negative for 1 •Transition every cycle communicates clock (but need 2 transition times per bit) •DC balance has good electrical properties V 0 .85 -.85 0 1 1 0 .1s Lecture 6 15-441 © 2008 11
4B/5B Encoding Data coded as symbols of 5 line bits >4 data bits, so 100 Mbps uses 125 MHz Uses less frequency space than manchester encoding Uses nrzi to encode the 5 code bits Each valid symbol has at least two 1s So never get three os in a row (Why dont we care about 3 ones in a row? 16 data symbols, 8 control symbols Data symbols: 4 data bits Control symbols: idle, begin frame, etc Example: FDDI ecture 6 15441@2008 12
4B/5B Encoding •Data coded as symbols of 5 line bits → 4 data bits, so 100 Mbps uses 125 MHz. – Uses less frequency space than Manchester encoding •Uses NRZI to encode the 5 code bits •Each valid symbol has at least two 1s – So never get three 0s in a row – (Why don’t we care about 3 ones in a row?) •16 data symbols, 8 control symbols – Data symbols: 4 data bits – Control symbols: idle, begin frame, etc. •Example: FDDI. Lecture 6 15-441 © 2008 12
4B/5B Encoding Data Code Data Code 000011110 100010010 000101001 100110011 001010100 101010110 001110101 101110111 010001010 110011010 010101011 110111011 011001110 111011100 011101111 111111101 ecture 6 15441@2008 13
4B/5B Encoding 0000 0001 0010 0011 0100 0101 0110 0111 11110 01001 10100 10101 01010 01011 01110 01111 Data Code 1000 1001 1010 1011 1100 1101 1110 1111 10010 10011 10110 10111 11010 11011 11100 11101 Data Code Lecture 6 15-441 © 2008 13
Other encodings 8B/10B: Fiber Channel and Gigabit Ethernet 64B/66B: 10 Gbit Ethernet B8ZS: T1 signaling(bit stuffing) Things to Remember Encoding necessary for clocking Lots of approaches Rule of thumb Little bandwidth>complex encoding Lots of bandwidth> simple encoding ecture 6 15441@2008 14
Other Encodings •8B/10B: Fiber Channel and Gigabit Ethernet •64B/66B: 10 Gbit Ethernet •B8ZS: T1 signaling (bit stuffing) •Encoding necessary for clocking •Lots of approaches •Rule of thumb: – Little bandwidth → complex encoding – Lots of bandwidth → simple encoding Lecture 6 15-441 © 2008 Things to Remember 14
Where we are We can send strings of bits We can keep the transmitter and receiver clock synchronized What next? ecture 6 15441@2008 15
Where we are •We can send strings of bits •We can keep the transmitter and receiver clock synchronized •What next? •Why? Lecture 6 15-441 © 2008 15