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2 Computer Networking notes: overview

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The network core

  • The mesh of interconnected routers

  • Packet-switching(个人认为这里泛指数据包。不同的数据交换)
    – Hosts break application-layer messages into packets, forward packets from one router to the next, across links (指hosts之间的链路) on path(指从源hosts到目标host的路径) from source to destination.

  • Packet switching cause delay and maybe loss
    – Store and forward cost the time
    – Queuing caused by excessive packets in the router costs the time
    – Packets may be dropped (lost) if the memory fills up2 Computer Networking notes: overview

  • Two key network-core functions
    – Routing: Determines source-destination route taken by packets. (算法计算出路径)
    – Forwarding: Move packets from router’s input to appropriate router.(按照计算出的路径把数据包传送出路由,路由器有多个端口。)

  • Alternative core: circuit switching (电路交换)
    End-to-end resources are allocated to and reserved for “call” between source and destination.
    2 Computer Networking notes: overview
    In the diagram, each link has four circuits.
    – Dedicated resources are no sharing, and it can guarantee the performance.
    链路及相关资源专有,不被分享,确保性能。
    – Circuit segment idle if not used used by call.
    导致了数据转发的空档期带来的资源浪费。
    –Commonly used in traditional telephone networks.

  • Two ways of circuit switching: FDM (Frequency-division multiplexing)and TDM (Time-division multiplexing)
    2 Computer Networking notes: overview

  • Comparing packet switching and circuit switching:
    – Basing on the link with same bandwidth and assuming users have the same bandwidth. Packet switching can make more people use network than circuit switching.
    – Packet switching is great for bursty data (数据突发性增长) since it is resource-sharing, simpler without call setup.
    – Excessive congestion maybe cause packets delay and loss, and it need protocols to improve the reliability of data transfer and congestion control.
    – It’s needed to make packet switch has the circuit-like behavior for solving some problems, like unstable audio or video services.

  • Internet structure: network of networks
    – End systems connect to Internet via access ISPs (Internet Service Providers), such as residential, company, and university ISPs.
    – Access ISPs in turn must be interconnected, so that any two hosts can send packets to each other.
    网络服务提供商相互连接(双向),所以网络中的任意两台主机可以相互发送数据包。
    – Network of netwoks become more complex, and evolution was driven by economics and national policies.

2 Computer Networking notes: overview

References

Sildes of Computer Networking, A Top-Down Approach

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