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Welcometo the internet architecture course
欢迎来到互联网体系结构门课程

Let's explore the mysteries of internet technology
我们一起来探索互联网技术的奥秘

Internet architecture
互联网体系结构

That's a big sounding name
名字听起来挺宏大的

Great things must be done in detail
天下大事必作于细

Right
对吧

We start small as god
我们从小的地方开始就像上帝

When god created man
上帝创造人的时候

It's a similar way
也是类似的方式

People are very complex systems
人是很复杂的系统

The human body is a very complex system
人体是很复杂的系统

The medical and life sciences research is focused on the molecular level
医学和生命科学的研究都是聚焦在分子层面

In other words
也说

The genes in every cell of our body determine our whole complex system
我们人体的每个细胞里面的基因决定了我们整个复杂的系统

Roughly similar features
大致相似的特点

The internet as a global network
互联网作为全球化的网络

It's huge
非常庞大

It's very complicated, right
非常复杂对吧

But on every internet host
但是在每台互联网主机上

You can look at it and see the whole picture
可以窥一斑而见全貌

You can get a general idea of how the entire internet structure works
可以大致上了解整个互联网结构的工作机制

We have a very big name in this course
我们门课尽管在课程名字上显得很宏大

But the point that we are looking at is the protocol stack on an internet host
但是我们研究的点还是集中在互联网主机上的协议栈

In particular
具体来讲

This course is going to be done as style learning by doing
这门课会通过“做中学”的方式

A working mechanism that understands the core of the internet in a easy way
由浅入深理解整个互联网核心的工作机制

First we will install the Linux system
首先我们会安装Linux系统

Some of you may not have used Linux
有的小伙伴可能没有使用过Linux系统

Just from the class
正好从门课

You can learn about Linux
可以学习一下Linux

We can use the commands from the Linux system
我们可以通过Linux系统的命令

Get a rough idea of some basic usage of internet-related commands under Linux
大致上了解Linux系统下的和网络相关的命令的一些基本用法

We also need to understand the basic functions of the internet through a Socket programming approach
我们还要通过Socket编程的方式来理解互联网的基本的功能

We will also compile the complete Linux system
我们还将编译构建完整的Linux系统

To keep track of the network protocol stack in the Linux kernel
以便通过跟踪Linux内核里面的网络协议栈

To take a closer look at the core of the architecture of the internet
来进一步剖析互联网的架构的核心

There's a lot of internet protocol
互联网的协议特别多

It's very complicated
非常复杂

We've chosen a few of the key protocols to do a detailed analysis to understand the working model of the internet
我们选择其中关键的几个协议来进行细致的剖析从而理解互联网的工作模型

We've chosen a couple of these protocols
我们选择了这么几个协议

The first is the TCP protocol
首先是TCP协议

Because TCP is the most widely used
因为TCP应用最广泛

Itis a reliable transport layer protocol for connectivity
它是面向连接的可靠的传输层协议

TCP is the most complex of all protocols
TCP在所有协议中算是最复杂的了

The next one is the network layer protocol
下一个是网络层协议

Because the IP protocol is the core of the internet
因为IP协议是互联网的核心

IP protocol packet format is relatively less complicated
IP协议封包格式相对并没那么复杂

And the key thing is the routing table
而起到关键作用的是路由表

Because all of the IP packet transfers are made through the query routing table
因为所有的IP封包的传输都是通过查询路由表来进行决策

Routing table
路由表

It's the heart of the whole internet
是整个互联网的核心中的核心

Responsible for routing IP packets
负责为IP封包选路

The network layer transmits data through the layer 2 link layer
网络层要通过二层链路层传输数据

There is a protocol called address resolution protocol ARP protocol between the 2 and 3 layers, through the layer 2 link layer and the physical layer
通过二层链路层和物理层来传输数据，在二层和三层之间有协议叫地址解析协议ARP协议

As the name suggests
顾名思义

It's the IP address of the IP layer and the physical address of the layer 2 link layer, or the MAC address
它是IP层的IP地址解析成二层链路层的物理地址，或者叫MAC地址

Only the MAC address is resolved
只有解析出MAC地址

To transmit the IP packets over the second layer
才能通过二层来承载IP封包进行传输

The ARP protocol and ARP cache are also key parts of our overall internet effort
ARP协议以及ARP缓存也是我们整个互联网得以有效工作的关键环节

Next is the layer 2 link layer
接下来是二层链路层

There is a lot of network
二层网络特别多

WIFI, 3G, 4G, and so on
比如说WIFI、3G、4G等

We are using more of the ethernet
我们用的比较多的是以太网

Ethernet is also the key to the development of the internet
以太网也是互联网发展起来的关键

And the network that we typically connect through the double stranded wire and the crystal head is the ethernet
我们常见的通过双绞线和水晶头连接的网络就是以太网

Ethernet is very widely used
以太网用的非常广泛

And the network size of ethernet can be very large
而且以太网的网络规模可以做的非常大

Like urban ethernet
比如城域以太网

Ethernet networks are also very fast
以太网的网络传输速度也非常快

There is a critical mechanism for ethernet switching networks
以太网交换网络有很关键的机制

Transmission network as a shared medium
作为共享介质的传输网络

To develop quickly
得以快速的发展

You can have a very large exchange network
可以组建非常庞大的交换网络

The key underlying functionality
里面关键的基础功能

It's the ability to forward filtering
转发过滤的功能

The learning, forwarding, and filtering capabilities of network switches
网络交换机的学习、转发和过滤功能

The forward filtering database is also the core
其中转发过滤数据库也是核心

And it's also a time to understand the workings of the internet
也是理解整个互联网工作机制的时候

A very important point
非常重要的一点

And how the network card works and so on
还有网卡的工作机制等等

So these are the kinds of protocols that we can use to get to the heart of the internet
以上我们选择这几种协议就可以了解互联网的核心

But at the end of the scale, the DNS protocol, which is the key protocol for the spread of the internet
但是最后还要加上DNS协议，也是互联网得以普及的关键协议

Because you are using the IP address
因为通过IP地址来上网

It's very inconvenient, right
非常不方便对吧

Memory IP address is very difficult
记忆IP地址非常困难

But with the domain name
但是有了域名之后

You can do domain name resolution
可以进行域名解析

Just remember the name of the website when you visit the website
在访问网页的时候直接记住网站的名字就好了

The DNS protocol is also the core of the internet architecture
DNS协议也是互联网架构中的核心

It's a key protocol that the internet has been able to spread effectively
是互联网得以有效普及的关键协议

While looking at the DNS protocol
研究DNS协议的同时

We connect the previous TCP, IP, routing table, ARP, ARP cache, and forward filtering network and we connect it effectively
把之前的TCP、IP、路由表、ARP、ARP缓存和转发过滤交换网络我们把它有效地串联起来

So you can track how the entire network protocol stack works
从而可以跟踪整个网络协议栈的工作机制

That's why we put the DNS domain name resolution protocol at the end
这是我们把DNS域名解析协议放在最后的原因

Through the agreements that we have chosen
通过我们选择的这几个协议

Effectively constitutes the core core of the internet architecture, understanding how they work with each other
有效地组成了互联网架构的核心核心部分，理解他们互相之间配合的工作机制

There is a general sense of the architecture of the entire internet in general
大致上对整个互联网的体系结构就有了本质上的把握

In the end
最后

This course
这门课程

By understanding the history of internet architecture evolution
通过了解互联网架构演化的历史

Why is it designed to be a distributed, decentralized structure
它为什么设计成分布式、去中心化的结构

Why did the internet architecture evolve into what it is today
互联网架构为什么演化成今天的样子

What are the design and implementation considerations behind it
背后有哪些设计和实现上的考虑

What are the functional requirements
有哪些功能需求上的考虑

And, of course, the weaknesses and shortcomings of the internet
当然还有互联网的缺点和不足

Why these defects and disadvantages
为什么会造成这些缺点和不足

Let's take a look at the history of the internet in general
我们从总体上来了解一下互联网的发展历史

And the philosophy or the origin behind the design
以及设计背后的哲学或者渊源像

We are going to be " learning by doing"
我们将以“做中学”的理念

Organize content in a progressive way
以循序渐进的方式组织内容

I want to have a relatively smooth learning curve
希望有相对平滑的学习曲线

And eventually hopefully it will be a little bit more easy for you
最终希望能达到深入浅出的效果

Through the course of this course
通过门课的学习

Let's take a look at the history of the internet
让我们一起来理解互联网的过去

Now and how the future of the internet evolves
现在以及展望互联网未来如何演化