1 Quiz 1 histogram L10: Network Systems Frans Kaashoek 6.033 Spring 2012 http://web.mit.edu/6.033 Some slides are from lectures by Nick Mckeown, Ion Stoica, Dina Katabi, Hari Balakrishnan, Sam Madden, and Robert Morris What have you seen so far? Systems Complexity Modularity Dtechnology/dt Hierarchy Therac-25 Client/service design Enforced modularity X windows Naming systems Gluing systems File system name space/DNS Operating systems Client/service with in a computer Eraser and Unix Performance Coping with bottlenecks MapReduce Client/service using network • Sharing irrespective of geography • Strong modularity through geographic separation OS OS client server request network2 Network is a system too! • Network consists of many networks, many links, many switches • Internet is a case study of successful network system domain-1 domain-2 domain-3 Todayʼs topic: problems and approach • Economical: • Universality • Topology, Sharing, Utilization • Organizational • Routing, Addressing, Packets, Delay • Best-effort contract • Physical • Errors, speed of light, wide-range of parameters Design challenge: what does the network do and what do hosts do? • Internet: best-effort Switch Asynchronous Multiplexing/Demultiplexing • Multiplex using a queue • Switch need memory/buffer • Demultiplex using information in packet header • Header has destination • Switch has a forwarding table that contains information about which link to use to reach a destination Queue Queue length3 Statistical multiplexing 0.1 1 10 100 1000 0 2 4 6 8 10Number of packetsTime"u1.data""u10.data""u100.data"Aggregate Internet Traffic Smooths 5-min average traffic rate at an MIT-CSAIL router Max In:12.2Mb/s Avg. In: 2.5Mb/s Max Out: 12.8Mb/s Avg. Out: 3.4 Mb/s https://mrtg.mit.edu/mrtg/dmz-rtr-1-ospf.16.html Networks are heterogeneous Link technology Bits/s 1000100001000001E+061E+071E+081E+091E+101E+11Tel modemWireless CDPDTel modemTel. modem2.5G wirelessBluetooth wirelessCable modem / DSLT1802.11 baseEthernetInfrared802.11b wirelessT3802.11a wirelessFast EthernetGig EthernetOC48 opticalOC192c optical10G EthernetOC768d(technology)/dt for networks Mooreʼs Law 2x / 18 months Highest Link Capacity 2x / 7 months Aggregate Internet Traffic 2x / 12 months 1 10 100 1,000 10,000 100,000 1,000,000 1980 1983 1986 1989 1992 1995 1998 2001 Normalized Growth since 1980 Speed of light 0x / 18 months! Bits/s per dollar 2x / 79 months (crude estimate) # Internet hosts 2x / 13.3 months Thanks to Nick Mckeown @ Stanford for some of these data points4 Internet: Best Effort No Guarantees: • Variable Delay (jitter) • Variable rate • Packet loss • Duplicates • Reordering End hosts implement everything else TCP email SMTP TCP email SMTP Reliable, flow-controlled connection Email addresses, To, Cc, etc. IP:
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