EECS 122University of CaliforniaBerkeleyNetwork Architecture Network hierarchy Layering PerformanceLink Layer Ethernet Wi-FiNetwork Layer Addressing Routing PhysicalInterfacePhysicalInterfaceSynchronous unreliable bit pipeData LinkControlData LinkControlAsynchronous reliable bit pipePhysical LinkNetworkNetworkAsynchronous routed pathFH DataPhysicalInterfaceSynchronous unreliable bit pipeData LinkControlAsynchronous reliable bit pipePhysical LinkNetworkAsynchronous routed pathFH DataTransport TransportPH Data PH DataTH DataEnd Node Router End NodeApplication ApplicationData !"## !Link: !!"#$%&#$'$ !%& ' #System:() * ()) ()() Throughput Delay Jitter*+Connection: Send W bits (window size)Wait for ACKsRepeatAssume that the round-trip time is RTT secondsThroughput = W/RTT bpsNumerical Example:W = 64KBytes = 512 kbits= 512x1,024 = 524,288 bitsRTT = 200msThroughput = W/T = 2.6Mbps, -#!-#++,!-$**, (..# ,$-$,&('//& '"-$#01&'& '& ('1&'&('//& ' (1&',2 3-$"!$%&$3-$"#$%'4&$3-$"$--3$#-$'*/- Random Multiple AccessSwitchingBridged Ethernet802.11* #0How to share a channel?Multiple Access MultiplexingALOHA: First random multiple access systemEfficient for many users, each with low utilizationTry; If collide, wait random time then repeat (CD)Analysis: Slotted Aloha efficiency 1/e = 36% * #0Ethernet: First version – CSMA/CDWait until channel is idle; try; if collide, stop, wait, repeatIdea: CS should improve efficiency if fast enoughWait random multiple of 512 bit times (exponential back off)Analysis: Efficiency 1/(1 + 5a), a = PROP/TRANS*%- !Ethernet: Later versions – SwitchedLarger aggregate throughputVLANs: partition in disjoint logical LANsLink AggregationEach port is in its own collision domainas opposed to a hub where all ports are in the same collision domainFast, GE, 10GEImproved modulation schemes*1 ! /- Flat AddressingLearningWatch source addressesAvoiding LoopsSpanning Tree Protocol(ID, presumed root ID, distance to presumed root ID)Note: Not very efficient; Not very fast*% !/25(5.56 57585*( 96:6:);. 9*:6:(;6 9(:(:);7 9.:(:(;* 96:(:.;8 98:(:(;-$<9%:-!-:$-!-;*$/- Service? Operations: Addresses, MAC, Hub, Switch, Learning, Spanning Tree MAC: Why not Aloha? Why Switch? Why Loops?*($+3**a - 5GHz, up to 54Mbpsb - 2.5GHz, up to 11Mbpsg - 2.5GHz, up to 54Mbps MAC: CSMA/CA with or without RTS/CTSDistributed (DCF):CSMA/CA using different Interframe Gapsmaintain network allocation vectorCentralized (PCF): access point polls nodes+$+3**0,If medium is idle for DIFS interval after a correctly received frame and backoff time has expired, transmission can begin immediatelyIf previous frame contained errors, medium must be free for EIFSIf medium is busy, access is deferred until medium is idle for DIFS and exponential backoffBackoff counter is decremented by one if a time slot is determined to be idleUnicast data must be acknowledged as part of an atomic exchange*$+3**4#,% !Virtual Carrier Sensing using Network Allocation Vector (NAV)$+3** Why not CSMA/CD? Objectives of new MAC? Why RTS/CTS? How does NAV work? Why different IFS? Why more than 2 addresses? Why different PHYs? Why multiple channels?56 5 Internetworking AddressingClass-BasedClassless: CIDR Routing.<(<5 !77((.6(.67 *(.6.(:.:1=.>$##:($..<(:..:(5 !5 7((.6(.67 *(.6.(:6:17:((:6:1,=6>$##:*$6*:6(:6:16:* <-$"$$%- !-$( Addressing reflects internet hierarchy 32 bits divided into 2 parts: Class A Class BClass C ,'80 !network host 00network host 1160network host 1240~2 million nets256 hosts?01 0,5 7 # !Suppose fifty computers in a network are assigned IP addresses 128.23.9.0 - 128.23.9.49Range is 01111111 00001111 00001001
View Full Document
Unlocking...