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
現在講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.當關註某一層級時，我們就可以忽略其他層級的實現細節。
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:
- 哪個應用得到data；
- 什麽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.
一句話來說：IP地址決定你連接哪臺電腦，端口決定你訪問這臺電腦之後，會與哪個應用通信。
下圖展示了各個不同的Ports:
常用的端口
既然TCP給我們提供了一個可靠的通信管道，那我們可以用這個管道做什麽呢？什麽問題又需要解決呢?
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為HTTP的協議進行通信。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 連接並發送一個請求，web server看到了就會返回請求，返回的document就會出現在客戶端的桌面上。
這裏老師給我們展示了一個栗子：
接下來老師要介紹telnet client，不過人們認為這不安全，因為這是一個old and less secure protocols.
Van Jacobson - Content Centered Networking
這裏是關於人物介紹，所以感興趣就留言吧~
Internet History, Technology and Security (Week 7)