Velocity Reviews > 100Mb networking... a few queries

# 100Mb networking... a few queries

T.N.O.
Guest
Posts: n/a

 09-11-2003
Why do they only have either 100 or 10 as speeds? why not have a 50Mb with
maybe a bit more range than 100.. just wondered.

Richard Malcolm-Smith
Guest
Posts: n/a

 09-11-2003
T.N.O. wrote:
> Why do they only have either 100 or 10 as speeds? why not have a 50Mb with
> maybe a bit more range than 100.. just wondered.

100 goes plenty far enough. I cant think of many cases where you would be
applying copper in the correct place and exceed the distance limitations.
Inevitably 100+metre runs should be fibre for one reason or another.

Michael Newbery
Guest
Posts: n/a

 09-11-2003
In article <bjossp\$lcjd7\$(E-Mail Removed)-berlin.de>,
"T.N.O." <(E-Mail Removed)> wrote:

> Why do they only have either 100 or 10 as speeds? why not have a 50Mb with
> maybe a bit more range than 100.. just wondered.
>
>

Leaving aside such curiosities as 1Mb Ethernet, there are 10Mb, 100Mb,
1,000Mb and 10,000Mb Ethernet. However, despite the impression that
using a 10/100 switch might give you, they are not very similar at the
bit (ISO layer 1) level. They are of couse essentially identical at
layer 2.

10M Ethernet uses a very inefficient mechanism called Manchester
Encoding, which transmits at 20MHz to send data at 10Mbps. I.e., 2 Hz
per bit.

100M Ethernet uses a more sophisticated encoding called 4B/5B, which
operates at about 30MHz. (31.25MHz to be precise)

The distance limits of 100Base-T are conservative and MOSTLY based on
signal loss in the cable (entirely based on signal loss/noise for
full-duplex operation).

For example, using fibre, you can get long range driver for 1000Base-F
(that's gigabit, not 100Mb), which will go about 150km!

So, the short answer to you question "why not have a 50Mb with maybe a
bit more range than 100?" is: there isn't any point. The cost far
outweighs the benefit.

--
Michael Newbery
surname at "actrix", 2ld "co", tld "nz"

Uncle StoatWarbler
Guest
Posts: n/a

 09-12-2003
On Fri, 12 Sep 2003 22:50:24 +1200, simon.A wrote:

>
> The main point is, the more power that you have thrown at the line will
> dictate what distance you can get. In the instance of Southern Cross, I
> belive

uh.. the 10kV feed is because all the repaters are connected in series. Each
one only drops a few volts (it's hard to run individual power feeds
underwater...)

T.N.O.
Guest
Posts: n/a

 09-12-2003
"Uncle StoatWarbler" wrote
> uh.. the 10kV feed is because all the repaters are connected in series.

Each
> one only drops a few volts (it's hard to run individual power feeds
> underwater...)

why not solar power... with big leads to a floating solar panel on the
surface...

sorry, I'm in a clean green mood today

Michael Newbery
Guest
Posts: n/a

 09-13-2003
In article <3f61a4d5\$(E-Mail Removed)>,
"simon.A" <(E-Mail Removed)> wrote:

> "Michael Newbery" <(E-Mail Removed)> wrote in message
> news:(E-Mail Removed)...
> >
> > For example, using fibre, you can get long range driver for 1000Base-F
> > (that's gigabit, not 100Mb), which will go about 150km!

> ------------------------
> Fibre is extremely variable in what distances it can go without repeaters,
> example, the main backbone cable from Christchurch to Dunedin has repeaters
> based in most towns (obvious reasons - pop), which leaves the maximum
> distance without a repeater about 60km. However, look at the Southern Cross,
> its about 150k or so between each repeater.
>
> The main point is, the more power that you have thrown at the line will
> dictate what distance you can get. In the instance of Southern Cross, I
> belive

At high speed, dispersion smears the waveform, which limits the distance
you can go without regeneration. You can aid by using dispersion shifted
fibre, but even that only works up to a point.

The drivers I'm refering to are special GBICs, which plug into a
standard GBIC port on a switch, and drive 100-150km on standard
dispersion fibre. They are fed up to 5.5VDC.

See
http://www.extremenetworks.com/servi...lidatedHWRev3-
Chapter10.asp (LX100)
and http://www.foundrynet.com/services/faqs/media.html (LHB)
--
Michael Newbery (email my .Mac account---my surname)