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

Tue Oct 16 18:45:44 EST 2007

Hi again Mark,

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

The D is a distraction in so far as the digital component starts at the 
DSLAM ( exchange ) and onto the internet backbone. Customer premises to 
exchange is still analog.

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

Great question about ISDN ...

By contrast ISDN ( Integrated Services Digital Network ) is digital all the 
way from the customer onwards. A special "digital" phone line is needed to 
set up ISDN. No such special line is needed to get your ADSL service up and 
running.
One can plug a normal analog phone on an ADSL link but not on an ISDN link. 
Another device called a Terminal Adapter sits between an analog phone and 
the ISDN service.  The ISDN and non ISDN devices have different voltages.
Interestingly ISDN is only a fallback/emergency type of service these days 
and not the primary choice of WAN link for organisations. The most common 
WAN technologies now are DSL and leased lines.
Most of this is knowledge covered in Semester 4 of Cisco CCNA - a VET 
subject . I don't own any shares in Cisco systems for the record, but 
teaching the course has made my configuring, understanding and 
troubleshooting of networks so much clearer.......

I think this is much more than ITA and more than SD frankly, but very 
useful, just like how to fix your car,
how to cook a nutritious meal and how to win friends and influence people 
through humour, sarcasm or anything else that works .........  :))

Keep well

Kevork

Kevork Krozian
Edulists Creator and Administrator
www.edulists.com.au
kevork at edulists.com.au

----- Original Message ----- 
From: "Mark Kelly" <kel at mckinnonsc.vic.edu.au>
To: "Year 12 IT Applications Teachers' Mailing List" 
<itapps at edulists.com.au>
Sent: Tuesday, October 16, 2007 12:41 PM
Subject: Re: [Year 12 IT Apps] VITTA ITA exam 2 - my ideas of errata

> 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
> Manager - Information Systems
> McKinnon Secondary College
> McKinnon Rd McKinnon 3204, Victoria, Australia
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>
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