[Year 12 IT Apps] VITTA ITA exam 2 - my ideas of errata

[Mark Kelly]

Hmmm!  The "D" in (A)DSL is a bit of a distraction then!

Does this mean that ISDN is therefore also not really digital?

(And I wonder how kids in the practice exam would have coped with the 
question that prompted this original thread! It's more SD than ITA.)

Kevork Krozian wrote:
> Hi Mark,
> 
>  Yes it is a complex area.
> The fact you can hear a dial up modem is not what modulation/demodulation is limited to as much as we have become used to it.
> The human hearing range is only incidental to the frequency of transmission. The fact transmission with mod/demod can't be heard in DSL/Cable modems does not change the point about use of waveforms/frequencies to model digital data. We just can't hear these frequencies. 
> 
> You are right. We have become accustomed to our senses dictating what the technology is doing just like a router then a modem to connect. In reality, a modem is just an interface that is now absorbed into the routers.
> 
> Now, I hope that hasn't caused more confusion ........
> 
> Back to work - exams are looming and the kids have been dragging their feet . 
> Back in my days ......
> 
> Keep well
> Kevork
> 
>>>> Mark Kelly <kel at mckinnonsc.vic.edu.au> 16/10/2007 8:17 am >>>
> Thanks, Kevork.  It is a complex topic once you start delving into it. 
> I suppose what I meant about modulation/demodulation is that cable and 
> DSL modems don't convert digital data to and from _sound_ as the dial-up 
> modems do.  Or at least I hope they don't  :-)
> 
> Wiki has an informative page on DSL - http://en.wikipedia.org/wiki/Dsl 
> 
> 
> Kevork Krozian wrote:
>> Hi Mark and Russell,
>>
>>  I would add a few more cents here to the discussion. 
>>
>> The primary role of a router is " path determination and switching"
>> meaning it decides which interface an incoming packet has to be sent out
>> and how to transfer 
>> - switch -  the packet to that outbound interface. Various modules
>> within routers ( eg. ADSL module, WAN modules ) can be used to provide
>> connectivity to a WAN without a modem. Also, routers can provide
>> security functions through firewall services, that is not their primary
>> role.
>> So, a router connects LANs to either other LANs or WANs - it is a
>> connectivity device for different networks. Compare with a switch which
>> is a connectivity device for devices WITHIN a network.
>>
>> Broadband modems ( DSL and cable modems ) use complex waveforms to
>> carry digital data ( http://en.wikipedia.org/wiki/Modem ) therefore
>> still modulate/demodulate and therefore are analog in nature. The term
>> broadband refers to the ability to carry multiple signals ( voice, data,
>> TV ) as opposed to baseband which carries one type of signal. 
>> A DSLAM ( Digital Subscriber Line Access Multiplexer ) is found at the
>> exchange which allows aggregation of incoming ADSL signals to connect to
>> the digital network (internet ) backbone. So, despite the publicity an
>> ADSL digital service is only digital up to the DSLAM after which it is
>> analog up to the customer premises. That is still better than dial up no
>> doubt.
>>
>> Cable modems act like a bridge between a customer's LAN and the coax
>> cable network of the provider though they can provide higher layer
>> functions such as routing and other tasks
>> http://en.wikipedia.org/wiki/Cable_modem . The point is there is no
>> sign of fibre optic media here. 
>>
>> As in past years, to all readers,  Cisco Networking Academy ( a VET
>> subject ) is the way to go if you wish to formally learn more about this
>> fascinating area of IT.
>>
>> Best Wishes
>>
>> Kevork
>>
>>
>>>>> Russell Edwards <edwards.russell.t at edumail.vic.gov.au> 15/10/2007
>> 2:22 pm >>>
>> Hi Mark, I agree with most of what you have said, just a couple of  
>> minor points
>>
>> On 15/10/2007, at 1:36 PM, Mark Kelly wrote:
>>> Question 1
>>> Which of the following enables several LANS to connect over a WAN?
>>> Suggested answer: D. Router.
>>>
>>> A router protects a LAN from the outside world, but its role is not 
>>> principally to enable communications.  I suspect the best answer  
>>> would be a modem.
>> The primary role of the router is indeed to enable communications  
>> between two or more networks. It may include a firewall of some sort  
>> (=protection from the outside world) but need not.   A modem is not  
>> necessary as you may have a data link that doesn't require modulation/
>>
>> demodulation-- though you'd be hard pressed to find one that could  
>> offer distances that classify as "wide area"!
>>
>>> Question 3
>>> Which type of backup uses two sets of backup media and backs up the 
>>> most recent changes on the second media?
>>> Suggested answer: B. Differential.
>>>
>>> This can*t be right.,  The question is very odd.  Two sets of  
>>> backup media? From http://www.backuptool.com/incremental% 
>>> 20backup.htm...
>> I suppose what they're getting at is that incremental backups might  
>> use more than twos set of media. But in fact, the terms are about  
>> _what_ you backup, _when_ -- not _where_ you put the data (i.e.
>> media).
>>
>>> A modem is, for most people today, a digital device for ADSL or  
>>> cable internet that has no modulation or demodulation happening!   
>>> The question should have referred to analogue modems if it wanted  
>>> this answer.
>> No, ADSL and cable are still analog modems. ADSL goes over copper  
>> line just as dialup, simply using a much higher (analog) bandwidth  
>> than plain dialup and avoiding the voice band. Cable modems (afaik)  
>> use an optic fibre data link so again this is a modem, as a carrier  
>> wave (in this case a light wave) is modulated to transport data.   
>> Even wireless, 3G or satellite internet will rely on a pair of modems 
>>
>> (with an electromagnetic wave as a carrier) as part of the link, even 
>>
>> though the term isn't usually used in reference to them.
>>
>> cheers
>>
>> Russell Edwards
>> Whittlesea Secondary College
>>
> 
> 


-- 
Mark Kelly
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