📄 lianxisd.txt
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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?
Answer: It stands for Extensible Markup Language . HTML tags are primarily concerned with how text should be displayed ,XML tags can be used to describe what a pieces of text means .Another major difference between them is that there are no predefined tags in XML.Users have the freedom to define their own tags .
b. Contrast the flexibility of using XML tags and HTML tags.
Answer: An HTML file is a text file containing a set of predefined tags that are used to specify how data should be displayed in a browser or another application program while there are no predefined tags in XML. Users have the freedom to define their own tags.
c. What is XSL? What is the function of XSL in terms of XML?
Answer: It stands for Extensible Stylesheet Language .In terms of the XML ,it is used to specify how an XML document would be interpreted and displayed by the browser .
d. What does a DTD file do?
Answer: It is used to describe how tags are used to organize the data .It used to ensure that all the documentation is formatted in the same way .Application can use the DTD to read and display the content of the document .
e. What is one reason why storing data in XML may be preferred to enable multiple systems to exchange data?
Answer: As a kind of text document markup language ,it is more independent ,users have the freedom to define the tags .
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:
Answer:1986
Score:
Answer: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.
Answer: <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>
<td><span datafld="Movie_id"></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.
Answer:
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?
Answer: It converts the Simulated signals to digital signals between binary bits and sounds transmitted as analog electrical signals over the telephone line .The noise is produced because of the interference that destroys the integrity of signals on a line .
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?
Answer: It stands for digital subscriber line technologies .Because its asymmetry ,it has a low speed of upstream transmissions but a high speed of downstream transmissions ,so the asymmetry can work very well for individuals running Web browsers ,where only a small amount of data travels upstream but large amounts of text and images (and maybe even streaming audio or video) are transferred downstream.
c. What is an ISP and what does it do?
Answer: It is short for the Internet Service Provider , stands for companies that maintains an Internet host computer
It provides Internet access to business and individual , charges monthly fee ,and offered over telephone lines ,cables TV, or satellite dish .
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?
Answer: An identifier for a computer or device on a TCP/IP network .
e. What service does an ISP provide to determine the destination IP address for a URL?
Answer: 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?
Answer: It keeps a list of IP addresses and corresponding LAN addresses for all the hosts on those networks.
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?
Answer: When a router receives a packet from one of them, one of two things can happen. If the destination IP address is in its host table, the router delivers the packet directly to that host, using the host's LAN address. If not, it must forward the packet to another router, hopefully one that is closer to the ultimate destination
A router stores a lot of IP address for the host 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 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?
Answer:3 ,The first three parts of the three IP address are the same ,but the fourth are different .
b. Why are there multiple IP addresses? (Hint: consider the workload the website encounters.)
Answer: Because one website may cover a large area ,so there are many people sent many requests to it at the same time ,if it use multiple addresses they can separate the work .
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"?
Answer: To look up www.yahoo.com the first step is to ask the DNS server for the com domain for the IP address ,then we ask that DNS server for the IP address of the DNS server for the yahoo.com domain .finally we ask that DNS server for the IP address of the host we are trying to contact .
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 to 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.
Answer: I type the web address in the http://www.linkwan.com/vr2/ to do traceroute.
My traceroute starts from my computer’s address.192.168.19.115
e. What is indicated by each part of "www.yahoo.com"?
Answer: www indicates the host name oc the organization’s front door web server ,yahoo indicates the 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?
Answer: It represents the server that 209.13.36.15
g. How many hops did it take to reach the destination?
Answer: 16
h. What is the IP address of the node that took the longest time?
Answer: 217.6.49.177
Do Traceroute to "www.yahoo.com" again.
i. Record the result of this command.
Answer:
j. Did the two Traceroute results show that the packets were sent through the same path? Explain your answer.
Answer: No ,the packets were sent through 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)?
Answer: I think the problem may be the server
l. What if your packets are lost after they have reached your ISP?
Answer: The problem may be the ISP server
m. What if your packets are lost just before it reaches your destination server?
Answer: The problem may be the destination server
n. Do a Traceroute to www.icarnegie.com. What may be a cause of the Tracert result?
Answer: Yes ,it is mainly because that my computer is behind a firewall ,the packets which has been sent are blocked
o. List two problems that may be diagnosed using Traceroute?
Answer: The first , it may diagnose which part of links malfunctions
The second is that 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.
Answer: No ,
b. What is your IP address?
Answer: 192.168.7.1
c. What are the IP addresses of your DNS servers?
Answer: 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.
Answer:
e. Did you get a response from the target server?
Answer: No ,I didn’t
f. List two possible explanation(s) for the result of the Ping command below:
Figure 2 Ping Result
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.
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