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In organizaons lans are formed using ethernet as a

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Unformatted text preview: case, the network exists independently as a complex, physical fabric, the use of which then must be mediated by complex, sophis=cated soKware. The Physical Fabric 11 vBNS OC3 T3 trunk ISP phone/ cable home network access point point-ofpresence T1 trunk ethernet The Physical Components 12       From the smaller to the larger (and ignoring wireless elements), individual machines in homes connect to a server in the service provider (ISP), using dial ­up lines (DS0), or cable (ISDN = 2*DS0), or digital subscriber lines (DSL). In organiza=ons, LANs are formed using Ethernet as a fabric and connected to a point ­of ­presence (POP) through (op=cal) T1 = 24*DS0 trunks. One step above we find T3 = 28*T1 trunks, giving access to network access points (NAP) that are linked by very ­ high ­speed backbone network services (vBNS) with links like OC3 = 84*T1, and above. Machines are Nodes that Host Components 13 host1 host2 host4 host3 Forming Networks 14   The Internet is a packet switched network.   A network (of networks) is formed by the routers that link them.   Informa=on from an applica=on is broken down into packets (also called segments, or frames, or blocks) to which control data is added (typically a header) to help the packets reach their des=na=on (across various autonomous, physical networks), there to be reassembled before delivery to the applica=on. Rou=ng Packets 15         On their...
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