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* Description: Network backbone device, such as modem, hub, bridge, switch, and router
* Compatiablity: RDBMS 11g, 12c
* Date: 11:25 PM EST, 05/08/2017
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<1> Modem [调制解调器/猫儿]:  
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     |__ Modulates one or more carrier wave signals to encode digital information for transmission and demodulates signals to decode the transmitted information.
         Transfer network signal wave to digital information that computer can interpret. The device is out of date, and almost retired. Central of Star topology.
		 
		 

<2> Hub [集线器]：		 
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     |__ Network device that connects nodes together, and transmit data packet amongs nodes for communication. Plugin, and then can be used immediate. 
         Input bendwidth shared by multiple output port equally. Hub is for broadcasting network, refers to transmitting a packet that will be received by every device on the network.
         Just plugin, and then can be used immediate. Input bendwidth shared by multiple output port equally, and cause network traffic.
		 Collision occurs when nodes send data packet simutenously. The device is out of date, and almost retired.


		 
<3> Bridge [网桥]：		 
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     |__ A smarter device than Hub which can record traffic info among nodes, and use the info to arrange most efficient data pass to aoviod traffic without broadcasting data to 
         every nodes in the network. However, both of Bridge and Hub are single direction data transmission. Sending and receiving data should happen in-syncly.
	
	
		 
<4> Switch [交换机]:		 
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     |__ Switch is for data packet transmission among nodes on LAN in bi-direction. In addition, there will be no need using broadcasting method with switch.
	 
	 
	 
<5> Router [路由器]：
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     |__ Router is for data packet transmission among nodes on WAN.
	 
         o. If you want to visit Emeralit.com website at home, you first send the HTTP request to the router in your living room. 
           ==> And then, the router will transfer the request to your ISP [Internet Service Provider] like Verizon. 
           ==> ISP will check Domain name in DNS server for the path of reaching Amazon.com web server.		 
           ==> After addressing the routing path to Amazon server, ISP will pass the request to the server. 
           ==> After Amazon received and finished dealing your request, it will send the HTML page back along the routing path where it come from.
		   
         o. Now, in the market, a common "router" is the combination of router and switch.