If you go shopping for network equipment today, you
could wander the store shelves endlessly and never encounter any of the
old-style Ethernet connectors - the round BNC coaxial type that we
discussed in our Ethernet tutorial. Instead, nowadays you are much more
likely to run into equipment like this, that uses keyed, rectangular
connectors that look a lot like modular telephone jacks...
(Click on above image for enlarged view)
The industry evolved to that point through a couple of evolutionary
steps. During a transition period that lasted through several years, it
became commonplace to find dual-mode equipment like this...
(Click on above image for enlarged view)
that had two different kinds of connectors, allowing you to mix and
match the old-style coaxial segments with the new-style RJ45 connectors.
(Just one little point of interest here: “RJ” stands for “Registered
Jack.”) You could buy dual-mode Ethernet adaptors for your PC, and
you could also find networking equipment like this, with dual connector
types.
The new-style cables and connector types are better and more convenient.
They’re less expensive, and much easier to install, and they can carry
the signals faster, giving you the ability to move your data faster and
better on the network. And inserting a new Ethernet cable into one of
these new modular connectors is literally a snap!
But in order to bring all these new benefits to modern Ethernet, the
technology had to evolve.
Let's think back to our original Ethernet tutorial and the discussion we
had about collision domains and segments. It may seem counter-intuitive
now, but it turns out that with this old original-style Ethernet, the
most complicated problem was detecting collisions. It was difficult for
a station at the far end of a network cable to determine if another
station, way at the opposite end, was interfering with its
transmissions. In order to make this work, engineers chose a specialized
coaxial cable of high quality, but even with that cable, the results
were marginal, and they couldn’t go any faster than 10 million bits per
second and still reliably detect those collisions. That’s why the
original, popular Ethernet standard was limited to 10 million bits per
second. Furthermore, this coaxial cable was rather expensive; it wasn’t
very flexible; it was awkward and cumbersome to string between many,
many computers in a large building; and a single point of failure on a
cable broke the whole network.
A lot of people observed that big office buildings were already wired
with telephone wires, and there was a search for a way to use standard,
low-cost telephone wires with a high-speed Ethernet, and somehow detect
collisions. |
