[LINK] terrabit per second internet
pbrooks-link at layer10.com.au
Wed Sep 9 10:18:07 AEST 2009
Roger Clarke wrote:
> At 21:51 +1000 8/9/09, David Boxall wrote:
>> What impressed me was to hear Aussies pronouncing router as 'rowter'.
>> When I was studying (just this side of the Jurassic) it was 'rooter'.
> As one of the rapidly declining band of guardians of Orstralian as
> she wuz spoke ...
> ... the word 'route' has been pronounced 'rowte' in the Australian
> military for a very long time.
> It's very difficult to sustain credibility in front of your troops if
> you say something like 'and for your final exercise prior to
> graduating as a driver, instead of me planning where you're driving
> tomorrow, you can all route yourselves'.
Yet oddly, in the military term 'route march' is always pronouced 'root
march', while a standalone 'route' prononced 'rowte' is a hasty retreat
- and when an army is 'routed (rowted)' and runs away they are probably
'rooted' as well.
Also, while router = rooter is through to be Australian, the router that
makes moulded edgings in timber has always been pronounced 'rowter' in
our house (from well before packet-directing routers were invented).
Anyhoo, back on topic (terabit-per-second optical switching, if you've
forgotten the subject line by now!) for a minute...
I ran a few calculations recently for a conference talk on 100Gbps
optical transmission technologies...
Did you know that at the speed of light in glass, a (todays) standard
10Gbps optical signal switches the laser signal on and off 54 times
before the first pulse has travelled just 1 metre through the fibre?
A 40Gbps optical signals (220 pulses per light-metre, or just 22
picoseconds between pulses) appears to be approaching a limit for
practical long-distance communications - the emerging 100Gbps
technologies are falling back to 10 parallel channels of 10Gbps, or
smarter use of 25 Gbps signals, but not any sign of real 100Gbps optical
signals being viable, because dispersion in the glass smears the pulses
together before it has travelled more than a few kilometres down the fibre.
Yes, the magic crystals may be able to switch terrabit per second
signals - but those signals will only be able to travel a very short
distance before they become smeared together, and on long-haul fibre I
suspect the bitstream will need to be split across many much slower
bit-rate channels to have much impact in the Internet.
(Telco Trivia: did you know that a 10Gbps optical channel between Sydney
and San Francisco acts as an optical delay-line memory, storing 745
Mbytes of data as photons inside the glass before the first bit pops out
at the far end?)
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