测量网络时间

APingRTT1)1-1UDPsendtorecvfrom(ms)()1A2)Tcpdump1ATcpdumpBSD(BPF)231BPF24-114-19BPF15-27BPF(1-13)80386BSD/OS2.0SparcstationELCSolaris2.4TcpdumpA.1PingRTT17PingICMPRTT()ICMPRTTA-1PingA-1PingICMPICMPPingRTTPingRTT8(8)8PingRTTA-2PingRTT1-13bsdisunRTT208Ping()A233A-2PingRTT1581001400(100)20IP8ICMPIP36~14281010RTTA-3InternetWANRTTyA-2A-3Internet(WAN)PingRTTPing:Ping:234TCP/IP3TCPHTTPNNTPUNIXLANWAN151010(RTT)InternetArizona(noao.edu)Netherlands(utwente.n1)252Connecticut(connix.com)London(ucl.ac.uk)ConnecticutArizona(connix.comnoao.edu)CaliforniaWashingtonD.C.(berkeley.eduuu.net)(Connecticutconnix.comBostonaw.com)Internet(16)(RTT)(1-13)A-2LANRTTWANRTT2bsdilaptopRTTWANA.2PingTcpdumpA-4PingTcpdump(127.0.0.1)PingA-4PingTcpdumpTcpdumpICMPIPIPICMPA-51.2UDPTcpdumpPingPingICMPIPIPIPIPICMPICMPICMPA-5UDPUDPA-4PingUDPPingICMP(211-21)UDPA-6bsdiPingUDPA235A-6()PingTcpdump(ms)TcpdumpUDPUDPUDPUDPIPIPIPIPyRTTPing(A-8RTT)UDPTCPT/TCPTCPT/TCPRTTPing2310020001008150815098PingRTT1508IPBSD/OS1536MTU(1508+20+8)1509IPUDP231002000(100)0150815090UDPUDPICMP(8)150815091509A-4A-5IP1508150925%4200BSDmbuf(22)(UDP0Ping8)mbuf100mbuf200mbuf3002048mbufmbufmbufmbuf(100)mbufmbuf2081-14BSD/OSMINCLSIZE(22-716-25)208101100mbuf1-1420014-11Web100~200A-6UDP1.5~2msUDPIPIPUDP(A5)1ms1msA-5Tcpdump4(IPUDPUDPIP)UDPTcpdump1.5~2ms()A-61.5~2msA-6UDP2.5~3msUDPTcpdump2.5~3ms236TCP/IP3TCPHTTPNNTPUNIXA237A-6PingTcpdumpPingTcpdump(PingICMP)PingTcpdumpPingICMPICMP1.31.4TCPT/TCP(1.6)A-7(1400TCP)A-7()TCPT/TCPTcpdump(TCPSYNT/TCPSYNFIN)(TCPFINT/TCPFIN)TCPTCPTcpdumpconnectFIN(1-8)T/TCPTcpdumpsendtoFIN(1-12)T/TCP(4ms)TCP(2.5ms)T/TCP(SYNFIN)TCP(SYN)4200mbufTCPT/TCP200A-6PingUDP(ICMPUDP)3mbuf(ms)(216.7sosend)(TCP)TCP1002100Tcpdump100TCPT/TCP4msT/TCP1-81-129TCP3TCPA-8A-6A-7PingUDPT/TCPTCPTcpdumpA-8()PingUDPTCPT/TCPPingPingUDPPingUDPT/TCPUDPUDP(1-12ACK)TCPT/TCP50%A-8UDPT/TCPTCP1-141A.3[Bellovin1992]238TCP/IP3TCPHTTPNNTPUNIXUDP:Ping:(ms)()RTT60ms()16msRTT32ms60msRTTTracerouteRTTRTT58msRTT80msT1(1544000bit/s)T3(45000000bit/s)(IanLanceTaylor)()T1100(30ms)5.215.180.03T3208ms178ms30ms1/6150000000b/s82ms52ms30msA-3y(202ms155ms)(98ms80ms)(30ms)T/TCPT/TCPRTTT1InternetT1InternetT1A-380ms193msConnecticutconnix.comArizonanoao.eduy80msRTT(Traceroute18ArizonaCaliforniaTexasWashingtonDCConnecticut)T114007.5ms1400RTT95ms193msA-91428T114287.5msA239A-91011ms17.5ms5ms1613.513.51ms14.511ms(2)251ms24ms1428476000b/sT11/33ms544000b/s()()552(512TCP)56kb/s80msT12.86msT30.10ms10T128.6ms()10T31ms()A-98.5124240TCP/IP3TCPHTTPNNTPUNIX5msT1T11ms10142891.5(24+97.5)1248525b/sT1TCPconnix.comnoao.eduTraceroute1280ms0.5ms187ms193ms95msA241