[HW] HW#03S 2020

[Prof. Hsiao]

Ture (select A in the homework system) or false (B).

Q1. There are in total 2^32 unique IPs for IPv4.

A. True. Since IPv4's address field is 32 bit long. 

Q2. For TCP, there are 2^16 unique port numbers.

A. True. Since TCP's source and destination port fields are both 16 bits long.

Q3. HTTP and POP3 are both client-server architecture. SMTP is not client-server

architecture (it is P2P architecture), since an SMTP host can both act as a client

and server.

B. False. HTTP is client-server, and POP3 is client-server. SMTP is still client-server. When a SMTP server acts as a SMTP client to push email to the next SMTP server, such connection is still client-server, because one of the peer play a roles as client and the other one plays a role as server. When we say "P2P", it means every peers can be a server and can be a client. However, your UA would never act as a SMPT server.

Q4. Both fiber and coaxial cable are employed in the cable system, it is often referred

to as hybrid fiber coax (HFC).

A. True. Nowadays, cable system uses fiber and coax at the same time to construct the cable system, just like Hinet uses fiber and phone line to provide DSL service.

Q5. “Multi-home” can provide a backup, in case one of the ISP fails to provide

service.

A. True. Campus and company network usually have more than one access links to prevent single point failure.

Q6. Suppose you would like to urgently deliver 40 terabytes data from Boston to Los

Angeles. You have available a 100 Mbps dedicated link for data transfer. You

would prefer to transmit the data by using FedEx over-night delivery.

A. True. For using FedEx over-night delivery, we assume the hard disk will arrive Los Angeles in 24 hours. As for the network transmission, if we only count transmission delay, it takes 37 days to deliver 40TB data. So, of course we use FedEx, which is much faster.

40 TB / 100Mbps = 40 * 10^12 * 8 bit / 100 *10^6 bps = 3.2 *10^6 s = 37 days

Q7. “YouTube” uses TCP for video transmitting. (Try to use Wireshark to monitor your

YouTube traffic)

A. True. YouTube use TCP. (You get points if evidence is provided.)

Q8. HTTP is a stateful protocol, since Cookie can remember some past information.

B. False. HTTP itself is a stateless protocol. Cookie is an additional mechanism built on the top of HTTP header. HTTP's response (including the status line and response headers) is made only depends on the request (i.e., request line and headers).

Q9. PTT uses “301 Moved Permanently” to redirect traffic from

http://www.ptt.cc/index.html to https://www.ptt.cc/index.html

A. True. (You have to provide evidence.)

Q10. NCCU uses “301 Moved Permanently” to redirect traffic from

http://www.nccu.edu.tw/ to https://www.nccu.edu.tw/

B. False. It use "302 Found" with "Location" header to redirect the page.

[思琪唐]

老師你好

有關第七題，我使用wireshark查出來的是UDP，如附圖。

請問這樣是否能加分呢？

謝謝。

Prof. Hsiao 在 2020年10月28日 星期三下午8:40:19 [UTC+8] 的信中寫道：

[Prof. Hsiao]

Hi,

跟任何(http/https)網站通訊之前, 都會有 DNS 的連線,

要把 domain name 網址轉換成 IP.

你所蒐集到的是你的電腦跟你的 DNS server 索取 youtube server 的 A record 的紀錄,

這個 DNS 是 UPD 沒有錯.

但是稍後你的瀏覽器會跟 Youtube 進行連線傳送影音資料的時候,

一般來說應該是 TCP 的連線.

你可以看看 A recoed 裡面寫了 youtube server 的 IPv6 位置是 2404:68xxxxxxxx

你如果繼續抓封包下去, 可以看一下你的電腦跟 2404:68xxxxxxxx 這一個 youtube 的 server,

兩者之間的連線是不是有 TCP 的連線.

Thanks,

Hsiao

ritat...@gmail.com 在 2020年10月30日 星期五上午11:50:53 [UTC+8] 的信中寫道：