Suppose within your Web browser you use http://ip/url.html to obtain a Web page. Further suppose that suppose the HTML file references two very small objects on the same
server, consisting of a small amount of HTML text. Let RTT0 denote the RTT between the local host and the server containing the object. Assuming zero transmission time of the object, how much time elapses using Non‐persistent HTTP with no parallel TCP connections()?
假设在 Web 浏览器中,您使用 http://ip/url.html 来获取网页。进一步假设 HTML 文件引用了同一服务器上的两个非常小的对象,由少量 HTML 文本组成。让 RTT0 表示本地主机和包含该对象的服务器之间的 RTT。假设对象的传输时间为零,那么使用没有并行 TCP 连接的非持久性 HTTP ()需要多少时间?
Note: setup connection once+ request 5 files concurrently +request 3 files concurrently
=2RTT0+2RTT0+2RTT0
setup connection once+ receive 8 files without additional request
=2*RTT0+RTT0
=3*RTT0
2*RTT0+8*RTT0
DNS的作用是域名和IP地址的映射
DNS协议运行在UDP协议之上
DNS协议端口号为53
缩写 | 全称 | |
SOA | Start Of Authority Record | 起始授权记录 |
A(v4)、AAAA(v6) | Address Record 地址记录 | 地址记录 |
CNAME | Canonical Name Record 规范名称记录 | 规范(别名)记录 |
MX | Mail eXchange Record 邮件交换记录 | 邮件交换记录 |
NS | Name Server Record 名称服务器记录 | 域名服务器记录 |
PTR | PoinTer Record PoinTer 记录 | 记录用于定义与IP地址相关的名称 |
A user requests a Web page that consists of some text and three images. For this page, the
client will send one request message and receive four response messages.
用户请求一个由一些文本和三个图像组成的网页。对于此页面,客户端将发送一条请求消息并接收四条响应消息。
Two distinct Web pages (for example, www.mit.edu/research.html and
www.mit.edu/students.html ) can be sent over the same persistent connection.
两个不同的网页(例如,www.mit.edu/research.html 和 www.mit.edu/students.html )可以通过同一个持久连接发送。
-If the connection did not timeout, then it can be used to send another html
request over the same port
- 如果连接没有超时,则可以使用它通过同一端口发送另一个html请求
With nonpersistent connections between browser and origin server, it is possible for a single
TCP segment to carry two distinct HTTP request messages.
通过浏览器和源服务器之间的非持久连接,单个 TCP 段可以携带两个不同的 HTTP 请求消息。
False – One TCP segment can carry only one HTTP request message.
False – 一个 TCP 段只能携带一条 HTTP 请求消息。
The Date: header in the HTTP response message indicates when the object in the response was last modified.
False – the time in the response message indicates when the request was generate.
True – not matter the response of the request is successes or not, at least the Status response should be returned.