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Help with some previous exam questions please

  • 04-05-2008 7:01pm
    #1
    johnplayerblue
    Registered Users, Registered Users 2 Posts: 747 ✭✭✭


    Hey
    Sorry if this is the wrong forum. I'm looking over some previous exam papers for an exam i'm doing next week and theres a couple questions that have be kinda stumped.

    1) Why must sound modulate a radio frequency carrier to be transmitted?

    And

    2) Give an example of application, network and link layer addresses in the
    Internet.

    The part i can't figure out on Q2 is the Application layer address?


Comments

  • #2
    DublinDilbert
    Registered Users, Registered Users 2 Posts: 5,401 ✭✭✭DublinDilbert


    johnplayerblue wrote: »
    Hey
    Sorry if this is the wrong forum. I'm looking over some previous exam papers for an exam i'm doing next week and theres a couple questions that have be kinda stumped.

    1) Why must sound modulate a radio frequency carrier to be transmitted?

    And

    2) Give an example of application, network and link layer addresses in the
    Internet.

    The part i can't figure out on Q2 is the Application layer address?

    Q1, there's lots of ways to answer this question really... basically electro magnetic energy does not propagate very well at low frequencies. At very low frequencies it will not propagate very far at all in air, and will need a very large antenna. Typically sound which a human can hear is in the range from 30Hz to 20KHz, even at 20KHz this will not propagate very far. Hence the sound is used to modulate a carrier wave of a much higher frequency. The carrier wave can either be AM modulated or FM modulated by the sound input wave form. The whole idea is that the carrier wave will propagate much easier through the air. Depending on the application a particular carrier wave frequency will be chosen as properties of how waves propagate will vary as its frequency is increased / decreased.


    Q2, within TCP/IP there are various address numbers used to make sure that the packets are delivered to the correct PC and to the correct application on the PC.

    An example of link layer addresses would be on an 802.3(Ethernet) network the hardware Ethernet MAC address which are used to get packets around the local network, but not used out on the internet.

    As you probably know in the network layer IP addresses are used, which are a software address, which is globally unique and will identify the machine.

    At the application level, an incoming packet must be routed to the correct application this is done using port numbers. This allows a packet to be routed to the correct application running on the PC, eg port 80 for a web server etc...

    Think of the IP address as the external phone number for a company, this is used by anyone trying to ring that company. Think of the port number as the internal phone extension within a company. IE once someone rings the company they need the internal extension of the person they wish to talk to....


  • #3
    johnplayerblue
    Registered Users, Registered Users 2 Posts: 747 ✭✭✭johnplayerblue


    Hi
    Thanks for the reply.
    I was reading i little more than i should have into Q2, the obvious answer was of course Ports but its the way the questions are phrased sometimes that make you second guess yourself, its the first time i've seen ports been refereed to as address and as for Q1,

    you said what i was thinking , there are quiet a few ways to answer it and again its just a matter of not over thinking the question and just go with the obivious answer, its a 4 pointer question so be stupid not to make double sure.
    I'm in for my 1st yr mobile exams on Thurs morning so i may just be back with a question or two more if thats ok.
    Cheers


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