ECE544Lec2DR08

ECE544Lec2DR08 - ECE544: Communication Networks-II, Spring...

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ECE544: Communication Networks-II, Spring 2008 D. Raychaudhuri Lecture II Includes teaching materials from L. Peterson
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Today’s Lecture Recap of network architecture & top- down design architecture paper discussion Shared media (MAC) protocols Ethernet Token ring IEEE 802.11
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Shared Media Networks Cable (Ethernet) Token ring (FDDI) Wireless (802.11,  DTDMA)
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Ethernet Overview History developed by Xerox PARC in mid-1970s roots in Aloha packet-radio network standardized by Xerox, DEC, and Intel in 1978 similar to IEEE 802.3 standard CSMA/CD carrier sense multiple access collision detection Frame Format Dest addr 64 48 32 CRC Preamble Src addr Type Body 16 48
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Ethernet (cont) Addresses unique, 48-bit unicast address assigned to each adapter example:  8:0:2b:e4:b1:2 broadcast: all  1 s multicast: first bit is  1 Bandwidth: 10Mbps, 100Mbps, 1Gbps Length: 2500m (500m segments with 4 repeaters) Problem: Distributed algorithm that provides fair  access
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Transmit Algorithm If line is idle… send immediately upper bound message size of 1500 bytes must wait 9.6us between back-to-back  frames If line is busy… wait until idle and transmit immediately called  1-persistent   (special case of  p- persistent )
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Algorithm (cont) If collision… jam for 32 bits, then stop transmitting frame minimum frame is 64 bytes (header + 46 bytes of  data) delay and try again 1st time: 0 or 51.2us 2nd time: 0, 51.2, 102.4, or 153.6us nth  time:  x  51.2us, for randomly selected  k =0. .2 n  - 1 give up after several tries (usually 16) exponential backoff
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Collisions A B A B A B A B
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Ethernet Bridging Bridge device for scaling network span Bridge Ethernet A Ethernet B Pkt forwarding table ..can “learn” from packet source addr
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ECE544Lec2DR08 - ECE544: Communication Networks-II, Spring...

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