计算机网络复习笔记

computer network note
    ISP:Internet Service Provider
    TDM：Time Division Multiplexing
    FDM：Frequency Division Multiplexing
    DHCP:自动获取ip
    ADSL: Asymmetric Digital Subscriber Line --not share bandwidth
    协议：

    A protocol defines the format and the order of messages exchanged between two or more communicating entities ,as well as the actions taken on the transmission and/or receipt of a message or other event.

    two most important protocols
        TCP:Transmission Control Protocol
        IP: Internet Protocol
    标准：
    Internet standards are developed by
        IETF:the Internet Engineering Task Force,also called 
        RFCs:request for comments
        whitch defined protocols such as 
        TCP,IP,HTTP,SMTP(for e-mail)

    specify standards:
        IEEE 802 LAN/MAN Standards Committee specifies the Ethernet and wireless WIFI standards

    distributed application:
        Voice-nover-IP(VoIP)
        P2P:peer to peer

    API:Application Programming Interface

    R:rate   S:speed   m:the length of the link
    R*d(prop)<1
    该链路上一个bit宽度=d/(R*d(prop))=d/(R*d/s)=s/R=速度/速率

    share a 2 Mbps link,each user 1Mbps when transmitting,each user tansmits only 20percent of the time

    circuit switching:2Mbps/1Mbps=2 users can be supported--telephone
    packet switchig:there be a queuing delay if three users transmmiting at                 the same time--tatistical multiplexing enables

    OSI 7 layers seven:A Presentation session T N 'Data link'
    host:application transport network link physical 5
    Router:network link physical                     3
    Link-layer switch:link physical                  2

    full text in English of RFC is request for comments

    all communication activity in Internet by protocols

    circuit switching is commonly used in traditional telephone networks

    there is no difference between a host and an end system

    end system not include router

    in addition to delay and packet loss ,another critical performance measure in computer net works is end-to-end throughput