networks_1

a host can be any device that has an ip address-- an ip address used to send and receive data in a network
ip address help identify devices and the  networks where they are located
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hubs,switches,and routers act as central connecting devices
central connecting devices are responsible for:1.connecting hosts 2.transmitting data

different central connecting devices perform these fuction in different ways

hub is for physical layer,send  message to every  pc (a waste of  bandwidth)

switch is for data link layer,he can learn the mac if the pc send message to him

router is for ip layer(网络层),link LAN to the Internet

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how do switches function?
1.hosts send data to a switch
2.switches direct data to its intended destination
3.unlike hubs,switches can send and receive data simultaneously(同时地)

4.switches are the most common device used to connect hosts to a network

coroutines with async and await syntax. 异步处理和等待语法的协同程序