Internet History, Technology and Security (Week 7)

Week 7

Technology: Application Protocols

Welcome to Week 7 of IHTS. This week has less material than other weeks. I like to think of it as a "seventh inning stretch" - where you get a little breather. This week wraps up the three weeks of "Technology" (i.e packets and stuff). After this week we have two weeks on Security and the final exam and then you are done. Thanks for sticking with it. You are almost there.
This week, we’ll be covering application protocols. With reliable 「pipes」 available from the Transport layer, we can build applications like web browsers, file transfer applications, or email clients and servers.

Layer 4: Applications

Application Layer

如今講Application Layer.

The services of the TCP layer are basically to give us a reliable, sequenced end to end stream, that can start in one application in one computer and end in an application in a different computer, and have a two way communication.

TCP give us a reliable pipe.當關注某一層級時，咱們就能夠忽略其餘層級的實現細節。

端口（port）：

像電話話號碼的擴展；
具體到某一個應用（application）。

關於應用層的兩個問題:

1. 哪一個應用獲得data；
2. 什麼規則和應用進行通話。
   

One is, which application gets the data. And this is done using a mechanism called ports, and ports allow a IP address, or a single computer, or a single server, to serve up multiple services, and then for a client to be able to dial up much like a telephone extension, and pick the service that they are interested in.

一句話來講：IP地址決定你鏈接哪臺電腦，端口決定你訪問這臺電腦以後，會與哪一個應用通訊。

下圖展現了各個不一樣的Ports:

經常使用的端口

既然TCP給咱們提供了一個可靠的通訊管道，那咱們能夠用這個管道作什麼呢？什麼問題又須要解決呢?

So, TCP gives us this reliable connection, we now can connect to the server that we desire to connect to by using ports, and the question is, what are we going to to say across that connection, and what we say across that connection, who talks first, what do you send, what comes back, depends on the kind of server that you are talking to。

即萬維網服務器。萬維網中的客戶端和服務端使用的是名爲HTTP的協議進行通訊。網址URL中的HTTP://dada.dada.dada就是。
下圖是 HTTP Request/Response Cycle.點擊一個運行在你電腦中的客戶端client的一個link，瀏覽器就會和web server 鏈接併發送一個請求，web server看到了就會返回請求，返回的document就會出如今客戶端的桌面上。

這裏老師給咱們展現了一個栗子：

接下來老師要介紹telnet client，不過人們認爲這不安全，由於這是一個old and less secure protocols.

Van Jacobson - Content Centered Networking

這裏是關於人物介紹，因此感興趣就留言吧~