What is the Internet?
- Simply speaking, millions of computing devices are connected by communication links, and among devices, routers and switches are key to transfer communication packets (messages).
- Apart from that, the Interconnected ISPs, protocols and Internet standards also make important roles in the Internet.
What’s the functions of Internet and what can we do through the Internet?
- The Internet provides applications with programming interfaces, allowing end users to enjoy services such as Web, VoIP, Email, games, e-commerce, social nets…
What is the protocol?
- Simply speaking, the protocol like the rules of communication among devices, and devices can understand each other as long as they use the same protocol.
打个比方， 如果两个人或多个人之间交流，并且交流的方式包含一些规则（暗号）；那么知道规定的人就能交流（明白对方的意思）。说白了，协议就是规定，每条规定代表固定的意思。 - Protocols define format, order of messages send and received among network entities, and actions taken on message transmission, receipt.
The network structure
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Network edge consists of hosts, clients and servers, and server are often in data centers.
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Hosts can access networks and physical media via wired, wireless links.
– Bandwidth: the rate of data transfer, bit rate or throughput, measured in bits per second (bit/s).
– Shared or dedicated. -
Interconnected router and the network of networks compose the network core.
– Internet is called network of networks because it connects computers all over the world forming a network. And all computers are also connected to each other , hence computers form a network and when they all join with internet it is called network of networks.
Access networks and physical media
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Distal Subscriber Line (DSL)
– Using existing telephone line to central office DSLAM
– Data over DSL phone line gose to Internet
– Voice over DSL phone line gose to telephone net
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Cable network:
– Frequency division multiplexing (频分复用)：Different channels transmitted in different frequency bands.
– HFC (Hybrid fiber coax,光纤同轴电缆混合网): asymmetric: up to 30Mbps downstream transmission rate, 2Mbps upstream transmission rate.
– Network of cable, fiber attaches homes to ISP router. Homes share access network to cable headend (电缆接头), unlike DSL, which has dedicated access to central office.
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Home network
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Enterprise networks
– Typically used in companies, universities etc.
– 10 Mbps, 100Mbps, 1 Gbps, 10Gbps transmission rate.
– Today, end systems typically connect into Ethernet switch. (Ethernet: 以太网是是一种计算机局域网技术标准) -
Wireless networks
– Shared wireless access network connects end system to router via base station aka “access point”.
Host sends packets of data
Host sending function:
- L: The application message breaks into smaller chunks, known as packets, and the length is L bits.
- R: Transmits packet into access network at transmission rate R (Link transmission rate aka (即) link bandwidth)
References
Slides of Computer Networking, A Top-Down Approach
