1.1 introduction

1.1.1 history

1.1.2 economic impact examples

• advertising-sponsored research
• e-bay
• crowd-sourcing众包; (尤指利用互联网)将工作分配给不特定人群

1.1.3 intellectual interest example 蛮重要的

可靠性（最根本）；规模扩大；带宽分配；安全问题

1.1.4 reinvention

from early 90s to 2012, from 1 million to 1 billion

1.2 Uses of Networks 基础知识点之一

• multiple users may access the same underlying resource. eg.
  • printer,search index, machines in the cloud
• enables remote communication with low latency
• statistical multiplexing (sharing of the network bandwidth according the user's statistical requests)
• content delivery
  • via replicas (reduce the network hops)
• gather sensor data

梅特卡夫法则 网络越大越好

1.3 Components

1.3.1 基本组成部分：

app用户应用、host主机终端、router路由器、link链路

app用户应用、host主机终端、router路由器、link链路

1.3.2 type of links 链路类型，按照方向分

• full duplex (bidirectional at the same time)
• half duplex (bidiractional not at the same time)
• simplex

1.3.3 wireless links

存在相互干扰的问题

1.3.4 a quick list of network 常见名词

常见名词列表 network类型，按照范围大小区分

1.4 The Socket API（Application Interface）

define how app use the network: let apps talk to each other via hosts

support two kinds of network services

• streams: reliably send a stream of bytes
• datagrams: unreliably send separate messages

以下是api作为一个interface的具体定义函数

api通信过程

1.5 Tracerouters

发明人

---------以上是component部分的相关知识---------

1.6 Protocols and Layers

1.6.1 definition 重要定义：划分网络功能层次的模型

Protocols and layering is the main structure method used to divide up network functionality

• each instance of a protocol talks virtually to its peers using the protocol
• each instance of a protocol uses only the services of the lower layer
  PS：They are guidelines, not strict
• may have multiple protocols working in one layer
• maybe difficult to assign a protocol to a specific layer

1.6.2 examples of protocols & stack of protocols

TCP, IP, 802.11, Ethernet, HTTP, SSL, DNS,... and many more

example of stack of protocols

Encapsulation is the mechanism used to effect protocol layering

• lower layer wraps higher layer content, adding its own information to make a new message for delivery

  
  

1.6.3 Demultiplexing

There's a little bit of information in the lower layer that tells it which port to go to in the next upper layer

1.6.4 Advantage of layering

wifi通过什么？和以太网连接

1.6.5 Disadvantage of layering

• adds overhead，but minor for long message
• hides information：app might care whether it is running on wire or wireless network

1.7 Reference models

1.7.1 OSI 7 layer reference model

• influential but not used in practice

1.7.2 Internet reference model 重要的实际网络四层模型

四层的功能划分 与七层模型的对应关系，以及常见名词的位置

1.7.3 protocol的建立者

1.7.4 units of data

1.7.5 devices

devices分别工作在不同的层次 我忘了它的重要性在哪里了

1.8 More details about history

1.8.1 APPNET

DoD = Department of Defense
telephone circuits

1.8.2 NSFNET (National Science Foundation)

1.8.3 MODERN INTERNET AND WEB