Re: Speed


"w2aew" <w2aew@xxxxxxxxx> wrote in message
news:1142176878.952755.73370@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
Jon,

Encoding schemes are used to overcome certain problems (long run
length, transmission spectra, clock recovery, etc.). While many
encoding schemes increase the BW, there are many that also decrease the
BW required. A good example is your old 56K modem. This uses an
encoding scheme that squeezes 56kilobits/sec through about 3KHz of
bandwidth on the phone line.

I would say that in most cases, when someone quotes a datarate, then
they are referring to the actual information rate, or resulting
bits/sec of real information, rather than the encoded or transmitted
baudrate.

In basic, digital baseband serial transmission, without encoding, the
basic frequency is equal to 1/2*1/bitrate, as explained above.

In the 10Gb/s optical transmission I mentioned - this is basically the
transmission rate. There's a standard for 9.953Gb/s transmission,
which includes the header, framing info, etc., so the actual "data
information rate", or "payload" rate is slightly lower. Many
transmission systems include forward error correction, which adds bits
and thus increases the signally rate for the same payload rate. Common
FEC rates are in the range of 11.5Gb/s to 12.5Gb/s for the same payload
rate as the unencoded 9.953Gb/s basic rate. The optical transmission
is most commonly done with simple two-level transmission (i.e. light=on
for a 1, light=off for a 0). Thus, for 10Gb/s, the maximum optical
square wave frequency is 5GHz.

Mainstream silicon bipolar and silicon CMOS process can produce devices
that support serial bitrates in excess of 10Gb/s. There are exceptions
of course. In many cases, more high-performance processes such as
silicon-gemanium, galium-arsenide, or other heterojunction
semiconductors are used for >10Gb/s. There are processes that produce
devices capable of operating at speeds in excess of 100Ghz.

There are ways of directly handling ultra high speeds like 1THz, but
generally these speeds are acheived in a parallel fashion - lots of
high speed signals processed simultaneously.


Ok, Thanks for the indepth explinations.

Jon


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