东北大学计算机网络平时测验1.pdf

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1、…东北大学考试试卷（测验一）总分一二三四五六七八学院………2015—2016学年第一学期…班级○课程名称：计算机网络（ComputerNetworks）…┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄┄……2.Circuitswitching.(15’)学号…1.Circuitswitchingversuspacketswitching.(10’)ConsidersendingapacketofFbitsoverapathofQlinks.EachlinktransmitsatRbps.The…a.Suppos

2、ethatallofthenetworksourcessenddataataconstantbitrate.Wouldnetworkislightlyloadedsothattherearenoqueuingdelays.Propagationdelayisalso密packet-switchingorcircuit-switchingbemoredesirableinthiscase?Why?negligible.…b.Supposethatallofthenetworksourcesarebursty—thattheyonlyoccasionallyhave姓名…a.Suppos

3、ethenetworkisapacket-switcheddatagramnetworkandaconnection-orienteddatatosend.Wouldpacket-switchingorcircuitswitchingbemoredesirableinthis…serviceisused.Supposeeachpackethash*Fbitsofheaderwhere0

4、leherebecausetherearenostatisticalmultiplexingb.Supposethatthenetworkisacircuit-switchednetwork.Furthermore,supposethatthe○gainstobehad,andbyusingcircuits,eachconnectionwillgetaconstantamountoftransmissionrateofthecircuitbetweensourceanddestinationisR/24bps.Assumingtssetup…bandwidththatmatchesi

5、tsCBRrate.Ontheotherhand,circuit-switchinghasmoretimeandnobitsofheaderappendedtothepacket,howlongdoesittaketosendthepacket?…overheadintermsofsignalingneededtosetupthecall,sothereisanargumentthat…packet-switchingispreferableheresincethereisnocallsetupoverheadwithc.Whenisthedelaylongerforpacketsw

6、itchingthanforcircuitswitchingassumingh=0.5.…packet-switching.Ifthiswereanexamquestioneitheranswerwouldbecorrect(asInterpretyourresult?…longasyouprovidethecorrectreasoning!).a.Thetimerequiredtotransmitthepacketoveronelinkis(1+h)F/R.Thetimerequiredto封b.Packet-switchingisbetterherebecausethereare

7、statisticalmultiplexingtransmitthepacketoverQlinksisQ(1+h)F/RThus,thetotaldelayforpacketswitchingis…gains—whenasourcedoesnothavedatatosend,itwillnotbeallocatedbandwidth(itQ(1+h)F/R+ts.…wouldbeunusedwhenthesourcehadnothingtosend).W