📄 lainixwu.txt
字号:
Take Assessment: Exercise 5
This is a resumption of your previous attempt.
Please note: At this time, we cannot track responses you entered previously. Please answer the following question(s).
If the assessment includes multiple-choice questions, click the "Submit Answers" button when you have completed those questions.
1. Go to bottom of question. Prerequisites: Exercise 4
Direction: Use a word processor (Microsoft Word) to answer the questions in the exercise.
Question1. XML and HTML
One necessary component to facilitate electronic commerce is the capability to exchange data over varying systems. In this section, you will strengthen your knowledge of XML as a portable language that enables data to be handled by any computer system.
a. What does the term “XML” stand for? What is the function of XML tags, and how does the function of XML tags differ from the function of HTML tags?
XML stands for “extensible markup language”.
The XML tags are used to define the fields of data, i.e. to describe what a piece of data means.
Compared with the function of XML’s tags above, the HTML’s tags are used to specify the format of a document.
b. Contrast the flexibility of using XML tags and HTML tags.
Given that HTML tags are predefined, you cannot use the tags which are not included in the HTML. However, XML tags offer more flexibility, because they are not predefined and you can create your own tags.
c. What is XSL? What is the function of XSL in terms of XML?
XSL is Extensible Stylesheet Language. XSL is used to control the display of the data which is contained in an XML file.
d. What does a DTD file do?
A DTD file contains the tags that are created by the users, and is used to describe how tags are used to organize the data.
e. What is one reason why storing data in XML may be preferred to enable multiple systems to exchange data?
One of the reasons is that the XML files are composed of text, software and hardware independent
Download and save Movies100EX.xml and display.html on your Desktop.
Open Movies100EX.xml using Notepad.exe to see the content of the XML file.
f. For the movie titled, “Top Gun”, list the following:
Year: 1986
Score: 6.4
Open display.html using Notepad.exe to see the content of the HTML file. Note that the references used to embed the xml file are highlighted in bold font below:
<html>
<body>
<xml id="movies" src="Movies100EX.xml"></xml>
This is a nice use of non-standard HTML. Do we really want to use IE only items. Also, since it is non-standard will the students have gained the knowledge necessary to answer this question?
<table border="1" datasrc="#movies">
<tr>
<td><span datafld="Title"></span></td>
<td><span datafld="Year"></span></td>
<td><span datafld="Score"></span></td>
</tr>
</table>
</body>
</html>
Drag and drop display.html into an Internet Explorer window to see how it is displayed.
g. Generate another HTML file that displays additional data fields from the XML file, listing Movie_id, Title, Year, Score, and Votes. Save the HTML file as, “myXML.html”. Copy and paste your HTML code.
<html>
<body>
<xml src="Movies100EX.xml" id="movies"></xml>
<table datasrc="#movies" border="1">
<tr>
<td><span datafld="Movie_id"></span></td>
<td><span datafld="Title"></span></td>
<td><span datafld="Year"></span></td>
<td><span datafld="Score"></span></td>
<td><span datafld="votes"></span></td>
</tr>
</table>
</body>
</html>
h. Use Internet Explorer to display myXML.html. Copy the screen shot of this file showing 20 movie entries and paste the screen shot into your assignment submission.
Delete Movies100EX.xml, display.html, and myXML.html from Desktop.
To learn more about this topic, you can go to http://www.w3schools.com/xml/xml_data_island.asp
Question 2. Network Transmission
In this section, you will explore different network components and trace through how a string, "http://www.cmu.edu", is transmitted from a computer at home, through a modem using services provided by an ISP, and reaches the website on the Internet.
When requesting a Web page, the user types a URL in a Web browser that converts the string into binary so that the computer can understand. The binary data is then transmitted as digital signals that are sent through the modem at home to the receiving modem maintained by the ISP.
Figure 1 Network diagram
a. How does a dial-up modem work? Can you explain the noise you would hear if you were to pick up the phone when the modem is transmitting data? What happens to the data at the receiving modem?
A dial-up modem works by converting from digital signals to analog signals.
When the modem is sending analog signals to the receiving modem, it is as if they are talking to each other. So when you pick up the phone, the tones you hear are the analog signals, just like the words of the modem.
At the receiving modem, the analog data transmitted from the lines is converted to digital signals again.
b. What is DSL, and why is it better than a dial-up modem?
DSL digital subscriber line) is a kind of services or technologies which use standard copper line to carry digital signals.
It is better than a dial-up modem because it’s speed is faster, and it allow the users to phone while they are getting on line.
c. What is an ISP and what does it do?
An ISP is an Internet service provider. It’s a company which provides Internet access to individuals or businesses, and changes fee monthly or yearly.
d. A website is hosted by a computer connected to the Internet. In order to reach the website on the Internet, your computer sends a request for an IP address through the ISP. What is an IP address?
An IP address is a unique, identifying number assigned to each computer connected to the Internet.
e. What service does an ISP provide to determine the destination IP address for a URL?
The ISP offers DNS (domain name service), by maintaining DNS servers which can convert the URL into a valid IP address. When you types in a URL, a domain name request is sent through your ISP to its DNS server, the DNS server then search its database to find a corresponding IP address and sends back to your computer.
f. After the IP address is returned to your computer, data is sent from your computer to the destination computer hosting the website. The data sent is split into packets. What information is contained in these packets?
These packets contain requests for Web pages, with the address of your computer, the destination IP address, sequence numbers, and some other data.
g. The packets of data are then sent to a router. What does a router do? What information does a router store? How does it handle packets?
A router is a device that is connected to at least two networks, makes decisions about the best route for data.
A router stores a list of IP addresses (a host table) for the hosts in the networks which it is connected to, and a list of IP addresses of its nearby routers.
If the destination address attached to the packets is in the router’s host table, the router will deliver them to the host; otherwise, the router must send these packets to another router. This process will go on until these packets reach their destination.
h. One way to ensure that the data is transmitted correctly is to use parity bits, which involves keeping track of the number of 1’s and 0’s the data should contain. Using even parity protocol, fill in the parity bits for the following data:
Data Parity Bit
00000000 0
01010101 0
11010101 1
01010111 1
11111111 0
10000000 1
Question 3. Live Networks
You will now use application programs to see a list of gateways through which a packet passes while traveling to its final destination:
Let’s first explore the properties of DNS servers using NSLookup, a program to query Internet domain name servers.
Go to an Internet website such as http://www.webreference.com/cgi-bin/nslookup.cgi or http://www.cosc.brocku.ca/cgi-bin/nslookup and enter the domain name "www.yahoo.com". You can also locate other NSLookup sites by searching for "NSLookup gateways" in http://www.google.com.
a. How many IP addresses are listed? How are they different?
3
An IP address is divided into four parts by three periods. The first three parts of each IP address are the same, and the last part of each address is different.
b. Why are there multiple IP addresses? (Hint: consider the workload the website encounters.)
Multiple IP addresses mean several Web servers for the website. When the request for the web pages or other requests become too much, these servers, each stores the website, can separate the work load.
c. Recall the function of a DNS server. How does a DNS server handle a request to a popular destination such as "www.yahoo.com"?
If the destination is a popular one, it means that the DNS server has already caches the results of the previous queries. So when your browser generates a domain name request, the DNS server directly find the IP address and sends it back.
Now let’s explore the properties of routers.
The program you will be using is called Traceroute. It is called Tracert in some systems such as Windows. The Traceroute program attempts to trace the route an IP packet would follow to a specified Internet host by sending three probe packets and then listening for a "time exceeded" reply from a gateway. If there is no response within a three second timeout interval, a "*" is printed for that probe.
In the Windows command console, at the prompt C:\, type "tracert www.yahoo.com". If that does not work for you, you may be behind a firewall. Try going to http://www.belnet.be/cgi-bin/traceroute, http://tcruskit.telstra.net/cgi-bin/trace, or http://visualroute.brd.net.au/. You can also locate other Traceroute sites by searching for "Traceroute gateways" with http://www.google.com.
d. How did you do Traceroute? From what site did your Traceroute start? Record the result of this command.
I got on the website http://www.linkwan.com/vr2/ to do traceroute.
My traceroute starts from 192.168.19.115, which is my computer’s IP address.
e. What is indicated by each part of "www.yahoo.com"?
“www” indicates the host name of the organization’s front door Web server; “yahoo” indicates its domain; “com” indicates the server is maintained by a commercial business.
f. What is the IP address of www.yahoo.com used in this Traceroute?
209.13.36.15
g. How many hops did it take to reach the destination?
16
h. What is the IP address of the node that took the longest time?
217.6.49.177
Do Traceroute to "www.yahoo.com" again.
i. Record the result of this command.
j. Did the two Traceroute results show that the packets were sent through the same path? Explain your answer.
No. The packets were sent through the different path.
Each router makes decisions about the best route for the packets based on the state of the available network links. The state of the network links changes every second, so each time you do the traceroute, the path will be different.
Traceroute command can also be used to determine where packets may have been lost. You can check the following:
-whether the packets were sent successfully from your computer to your ISP
-whether the packets were sent successfully from your ISP to the destination
k. Using Traceroute, you noticed that your packets were lost before they reach your ISP server. Where may the problem be (your server, your ISP server, or the destination server)?
The problem will be in my server.
l. What if your packets are lost after they have reached your ISP?
The problem will be in the ISP server.
m. What if your packets are lost just before it reaches your destination server?
The problem will be in the destination server.
n. Do a Traceroute to www.icarnegie.com. What may be a cause of the Tracert result?
The result is request time out.
It is mainly because that my computer is behind a firewall, the packets that’s sent are blocked.
o. List two problems that may be diagnosed using Traceroute?
1. it may diagnose which part of links malfunctions.
2. it may also diagnose which nodes in the Internet have problems.
Question 4. Network Failure
In addition to Tracert, other network tools such as IPconfig and Ping can be used to troubleshoot network issues.
You can use ipconfig command to see whether your computer is connected to the Internet.
Pull up the command console. Type “ipconfig /all”.
a. Are you connected to the Internet? Paste the screenshot showing the result of the command, ipconfig.
Yes.
b. What is your IP address?
192.168.19.115
c. What are the IP addresses of your DNS servers?
202.117.80.3
You can use Ping to test the response of the destination server.
d. First, launch the Windows Command Console. Type, “ping www.yahoo.com”. Copy and paste the screenshot of the Ping command.
e. Did you get a response from the target server?
No, I didn’t.
f. List two possible explanation(s) for the result of the Ping command below:
1. The host with this IP address 216.109.118.71 doesn’t exist.
2. The host exists, but the links between it and your computer has broken down and you can’t get access to the host.
Figure 2 Ping Result
Your grade will be based upon the following:
Questions
1. XML and HTML (16%)
2. Network Transmission (40%)
3. Live Networks (32%)
4. Network Failure (12%)
Go to top of question.
⌨️ 快捷键说明
复制代码
Ctrl + C
搜索代码
Ctrl + F
全屏模式
F11
切换主题
Ctrl + Shift + D
显示快捷键
?
增大字号
Ctrl + =
减小字号
Ctrl + -