[Year 12 IT Apps] Re: Modems and Routers thread..

[Russell Edwards]

On 15/10/2007, at 4:36 PM, Kent Beveridge wrote:

> Scuse my ignorance, but where would a multiplexor fit here, or  
> wouldnt it? Yep, I know its not the question, but now I just got  
> curious!

A multiplexor is a device for sending more than one communication  
"channel" (virtual dedicated connection) down a single physical  
connection.  Nowadays most network traffic is packet switched so this  
does the multiplexing by default-- the packet header identifies which  
"channel" it pertains to and the actual data link just sees packets  
without caring what's in them.   This would be a form of "time  
division" multiplexing.   Another type of multiplexing is frequency  
division. This is how DSL works on a phone line. Voice and dial codes  
etc all take up a different part of the frequency spectrum to the DSL  
modulation... Roughly (off the top of my head), the boundary is at  
about 8 kHz, and the "line filter" you have to use on any handsets is  
to enforce that cutoff so that there's no interference between the  
DSL and voice services.  Sending more than one signal down an optical  
fibre using different wavelengths of light is another example, as is  
sending multiple signals across a given band in the radio spectrum as  
in wireless networking or mobile phones.

Russell



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