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Thread: Questions About My Computer Science Textbook

  1. #1 Questions About My Computer Science Textbook 
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    Greetings everyone, I'm a newcomer here and I just enrolled in an information systems class at my local community college. I'm on chapter 2 so far, and I have a bunch of questions that the text does not answer, and my teacher is either too busy to answer or gives a very vague answer. So that's why I'm here. Any anwers would help greatly, I would really appreciate it. I'm going to declare myself a computer science major most likely, so I will probably check this forum more often. Thanks in advance folks.

    1. The text says on pg. 76 that Wi-Fi sends signals to a communications device that is connected to a high-speed Internet service. Let's say a user goes into Starbucks and gets on Wi-Fi, what is the communications device that is recieving the signal? And isn't Wi-Fi an Internet service itself? So the communications device is connected both to Wi-Fi and another service simultaneously? The examples of this other service were Cable and DSL, which you can't get at Starbucks, so it confuses me.

    2. On pg. 78 the text says AOL regulates the Internet services to which members have access. Why would they do this and can you please give me an example of this?

    3. On pg. 78 the text says AOL is an OSP but that it offers free access to its services to anyone with a broadband connection. This confuses me because wouldnít a subscriber already have Internet through AOL instead of also needing broadband the text speaks of?

    5. Does google.com have a unique IP address? Isnít it too big to be based on one server or mainframe? The understanding that Iím getting is that every computer has an IP address, but not all computers have domain names. And every Web site has a domain name, but not all of them have IP addresses. Is this true of do all Web sites have an IP address? Also, can multiple servers or computers share an IP address?

    6. Besides for going through a registrar, what other means do individuals or
    companies use to register a domain name?

    8. On page 80 the text says that the Internet stores domain names and their IP addresses using the domain name system. Where and how does the DNS store domain names and IP addresses? What would happen to these domain names and IP addresses if they werenít stored?

    9. On page 80 the text says when you specify a domain name the DNS servers take action so data and information can be routed to the correct computers. I feel like Iím reading another language with this sentence, can you explain it in more basic terms? When and in what situation does someone specify a domain name, and what is this correct computer the text speaks of?

    10. CNN.com always has changing material, but users canít modify the content of the Web page. (If I am missing something and they can, letís just say they canít for the sake of the question). Since by definition a dynamic Web page is one users can modify, does that mean CNN.com is a static Web site, even though itís content is always changing?

    11. Can you please give an example of a Web server?

    12. What other types of servers are there besides for Web servers (WWW)?

    13. Do Web servers have to increase their size as they get more traffic?

    14. On page 82 the text talks about downloading Web pages. I always had the impression that downloading meant that itís stored into your storage media. Web pages donít do this, do they? Downloads arenít necessarily always stored on oneís computer, correct?

    18. It seems most of what is on the Web is free. What specifically do content aggregators offer that you wouldnít otherwise be able to see? Can you give an example of a content aggregator that is well known?

    21. What is the purpose of SMTP and POP3? What would e-mail be like without these communications protocols?


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  3. #2 Re: Questions About My Computer Science Textbook 
    Forum Cosmic Wizard SkinWalker's Avatar
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    I'm a little pressed for time, so I'll only be able to answer the first two or three.

    Quote Originally Posted by alexh519
    1. The text says on pg. 76 that Wi-Fi sends signals to a communications device that is connected to a high-speed Internet service. Let's say a user goes into Starbucks and gets on Wi-Fi, what is the communications device that is recieving the signal? And isn't Wi-Fi an Internet service itself? So the communications device is connected both to Wi-Fi and another service simultaneously? The examples of this other service were Cable and DSL, which you can't get at Starbucks, so it confuses me.
    Strictly speaking, WiFi is a network method. You can have two or more devices connected via WiFi and not have them connected at all to the internet. However, the most oft used configuration is device --> WiFi --> Router --> Modem --> Internet. The modem could be connected to the internet via cable, DSL, ISDN, T2, Dialup, Satellite, etc. So, accessing the internet at Starbucks via WiFi might actually be putting you on a DSL line or even Cable -depending on what ISP that particular location is using (I think they all use AT&T, which could mean either of these as well as UVerse.

    2. On pg. 78 the text says AOL regulates the Internet services to which members have access. Why would they do this and can you please give me an example of this?
    I am not nor have I ever been an AOLamer (old internet joke), but I would assume this implies that different levels of customer might have different services. A business client, for instance, might have server space for a webpage and access to commercial products to handle purchase transactions (credit card services, PayPal, etc.). It could also just meant that some services like UseNet and webserver space are tiered along with bandwidth.

    3. On pg. 78 the text says AOL is an OSP but that it offers free access to its services to anyone with a broadband connection. This confuses me because wouldnít a subscriber already have Internet through AOL instead of also needing broadband the text speaks of?
    Remember those server spaces for personal and commercial websites? You want anyone with internet to access them for obvious reasons. AOL also has several services like television, music, video, etc. that it makes available to all internet users. Their ISP services get the user to the internet. Their media services brings their media (and associated advertising) to these customers as well as to the ISP customers of AT&T, Comcast, Roadrunner, and everyone else.


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    Thank you kindly for the response. You said Wi-Fi is a network method. Pardon my ignorance but I am just beginning to learn the basics of computers.

    What's the difference between a network method and an Internet service such as cable or DSL?
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  5. #4  
    Forum Cosmic Wizard SkinWalker's Avatar
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    A network is two or more computers connected to share resources (files, drives, printers, etc.).

    In essence, the internet itself is a network (a very big one) but two computers connected with a CAT 5 cable and a couple of Network Interface Cards (NICs) would also be considered a network if they could share a printer and files.

    There are many different kinds of networks and what I describe above is a very basic home network. But you can have a more elaborate one at home or a small to medium sized business by using a Network Hub and a Switch, which connects computers together. Sometimes a Hub and a Switch can be the same piece of hardware, but mostly they're not. These allow for many computers and printers to share their resources and for certain software to take advantage of this (network enabled applications like databases, spreadsheets, etc. -even games). The switch allows for increased distance with cabling like CAT5 (signals degrade with cable length and the switch boosts the signal). CAT5 Cable is the most used these days, but you still some RG58, which is much like cable TV line.

    You can substitute the cable of one or more nodes of the network (each computer workstation is a node; so is a printer) with WiFi, but you have to then deal with problems of security, signal, RF interference, compatibility, etc. Security is a very real issue and the good thing about Cable is that it is relatively more secure than radio, which is what WiFi is. Bluetooth is another radio network medium (or method if you prefer), though it has a much smaller, narrower range. You can use just about any method or medium you can modulate a signal across if you really wanted, even laser. They all have their pros and cons in security, range, signal loss, bandwidth, packet efficiency, etc.

    Internet is a just what it says: an inter-network. Think of many, many different networks connected together by IP addresses and if you think of IP addresses like phone numbers it helps. Imagine your phone at home. By picking up a receiver, you can dial a 10 digit number and reach just about anyplace in the United States (different number of digits and country codes would apply to the entire world). Your home phone is a single node on a network, which is the entire phone system. But if your phone is handled through Pacific Bell, and mine is handled by Southwestern Bell, and our mutual friend is on the Sprint network, we can all still call each other using the same agreed upon system of country codes, area codes, local exchanges and local node numbers (the last four digits of U.S. phone numbers).

    The same is true for the internet in many, if not most, respects. An IP address is very much like a phone number in that ISPs get assigned certain ranges of IPs. These ISPs can then determine which of their users get which unique IP addresses. And the combinations and permutations of IPs are far greater than with phone numbers. Even still, most users have a dynamic IP, which means it can change depending on how long their modem "leases" the connection. Sometimes you can log off, reboot your modem, and your ISP will even give you back the same IP address.

    So, there really isn't a difference between a network method or medium and the Internet (such as that provided by cable or DSL). The internet is an amalgam of mediums and methods ranging from WiFi, WLAN, DSL, dial up phone lines, RG58, CAT5, Satellite, fiber optics, and probably many more.

    And I never expected to type so much about this! Whew! I didn't even mention about servers, which are integral to the internet as well as intranets (networks that are independent of the internet, but can have "gateways" to it).

    Maybe someone else will take some shots at alex's questions?
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    Thanks for the response, Skinwalker. I will admit some if not a lot of that was confusing, but I'm sure that with enough learning and research on my part that I'll get the hang of it. I'm going to try wikipedia for a lot of those key words. Chapter 3 is going to be on application software. Can't wait!

    (By the way, I just discovered this new site called "Quora" at quora.com. It is kind of like Yahoo answers with a LOT more knowledge base and depth. Check it out if you have the time.)
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    I'll take a shot at some of these

    5. Does google.com have a unique IP address? Isnít it too big to be based on one server or mainframe? The understanding that Iím getting is that every computer has an IP address, but not all computers have domain names. And every Web site has a domain name, but not all of them have IP addresses. Is this true of do all Web sites have an IP address? Also, can multiple servers or computers share an IP address?

    yes google has a unique IP - several, in fact.
    ok first of all Google is way way to big to be based on one single server. Rather its a "farm" of servers each dedicated to a specialized function. Some are spiders that go out and get data and content from the web and classify it. Others store all of that information. And still others are exposed publicly - they show the google.com homepage and collect the queries from the user and display the results. There are usually multiple external servers sitting behind a "load balancer". The load balancer is a machine that knows the IP addresses of the individual servers. When a request for the page comes to it, it looks to find the server that is least "busy" and routes the request to that server. This is ONE way (there are others as well) a "farm" of webservers can have one IP - the IP of the load balancer.

    Not all websites have their own dedicated IP address. In webservers you can do shared hosting, where multiple websites share an IP address. The request comes to the webserver and it looks at the domain (called a host) to see what website should be returned.

    Also keep in mind that any machine can have more than one IP address. The Network card will be associated to one or more IP's (as long as they are distinguished from one another in some form).

    6. Besides for going through a registrar, what other means do individuals or
    companies use to register a domain name?

    Some companies host their own DNS Servers and just add the domain there. They tell their ISP how to get to their DNS server for updates.

    8. On page 80 the text says that the Internet stores domain names and their IP addresses using the domain name system. Where and how does the DNS store domain names and IP addresses? What would happen to these domain names and IP addresses if they werenít stored?


    The Domain to IP data is stored on a DNS Server (different DNS server brands have different means) as a file (either a database file, flat file, metadata, etc). If this data wasn't stored to a permanent storage location, when the machine was rebooted all of the Name to IP mappings would be lost.

    9. On page 80 the text says when you specify a domain name the DNS servers take action so data and information can be routed to the correct computers. I feel like Iím reading another language with this sentence, can you explain it in more basic terms? When and in what situation does someone specify a domain name, and what is this correct computer the text speaks of?


    A: The DNS server receives a request from someone, like "Get the Location of Google.com on the internet". It looks up in a table the name Google.Com (and if it can't find it, it asks another DNS server) and gets the IP Address that google.com is associated with. It sends that IP address back to the requester. Now that the requester has the IP, it can communicate to that IP in the way it needs to (HTTP. FTP, SMTP, etc)

    B: People use Domain Names because they are easier to remember and manage than the IP Addr like 175.38.20.101. They also use domain names when they are sharing a single IP and need to differentiate between websites.

    10. CNN.com always has changing material, but users canít modify the content of the Web page. (If I am missing something and they can, letís just say they canít for the sake of the question). Since by definition a dynamic Web page is one users can modify, does that mean CNN.com is a static Web site, even though itís content is always changing?

    A: Static websites are sites where you, the user, go and read the content, but you do not CHANGE or CONTRIBUTE or CREATE content. The content is chosen by the owners of the site, not the users. Contrast that with WikiPedia.org where users are the ones that add or modify the content. That is known as Dynamic (or also, Web 2.0 *rolls eyes* its a cliche term)

    11. Can you please give an example of a Web server?

    a: Apache and Microsoft Internet Information Services are two big name webserver technologies.

    12. What other types of servers are there besides for Web servers (WWW)?

    a: DNS server, Database Servers, Mail Servers (SMTP), FTP Servers, etc

    13. Do Web servers have to increase their size as they get more traffic?

    a: That all depends. The more users coming to your site, the bigger the bandwidth they consume. It's like a highway - there is a limit to the width ( lets say 2 lanes) and the more cars on those two lanes, the slower everything goes. So more users means you will need to expand your bandwidth. Also, everytime a user requests a page, especially if it runs server side code, there is processing involved on the server (CPU time). While a webserver is designed to handle multiple requests at the same time, the CPU and Memory space is not infinite, and eventually you will notice a performance decrease. So I would say yes - Size as in Bandwidth and size as in CPU+Memory.

    14. On page 82 the text talks about downloading Web pages. I always had the impression that downloading meant that itís stored into your storage media. Web pages donít do this, do they? Downloads arenít necessarily always stored on oneís computer, correct?

    A: no, the pages are always stored to the client machine (your computer) even if you have your cache turned off (except in the cases with like google Chrome's Private Mode). The pages and images and CSS and other supporting files are downloaded to a temporary cache folder. This speeds up future requests for that same page because instead o having to go over the net to get it, the browser looks at local storage. moreover, if every page you viewed, and all of its images, javascript, css, etc were stored in browser memory, you would find yourself running out of memory quickly. When you have caching turned off, those resources are deleted when the browser has completed its need of them.

    18. It seems most of what is on the Web is free. What specifically do content aggregators offer that you wouldnít otherwise be able to see? Can you give an example of a content aggregator that is well known?

    Content Aggregators "spider" the web and collect information (content). Google and Bing are well known content aggregators, but there are other things like news feed aggregators and blog aggregators. They collect "relevance" information that you wouldn't normally see by looking at the whole picture of what they've taken (a page in a football website about The Gators is relevant to NCAA), they also pick up tags in the HTML code of the page to try and collect relevancy. They also look at pages that link TO this page and links to OTHER pages to try and establish the "meaning" of the content on the page. That's not normally something some can see.

    21. What is the purpose of SMTP and POP3? What would e-mail be like without these communications protocols?

    SMTP (Simple Mail Transfer Protocol) Establishes to each client exactly HOW it needs to be spoken to get things SENT. POP3 (Post Office Protocol) establishes to each client the rules and what needs to be spoken in order for users to GET mail. Without these protocols, the clients and servers wouldn't know how to talk to each other. It'd be like a french guy who only speaks french talking with a chinese guy who only speaks mandarin. Some form of standard must be used for both to know how to communicate.

    Hope this helps!
    TheNerd
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