This week, let's talk Internet structure! Oh yeah, baby...
let the good times rollout and rollover. Using words like
backbone and NAP and brouter, let's dig into the nitty-
gritty behind-the-scenes stuff that gets one web page from
a server in Walla Walla to your laptop in a hotel room in
Las Vegas, or a file on your office computer to your mother-
in-law's house in Moosejaw.
How does data get from you to me? How does my web page get
to your desktop and all the places it has to go and things
to do in between? What pieces of equipment lie in between?
Wow. When you think about it, it's just amazing what we can
take for granted nowadays. The stuff of science fiction
books and Gene Roddenberry series.
The Hard Parts
Okay, I'm not going to insult your intelligence by
beginning with definitions of LAN and WAN–-I'm assuming
you've come at least that far in the game. And I'm going to
assume you know the difference between a workstation and a
server – cuz otherwise, YEEESH. So, this section covers
everything between you and another computer hosting a web
page somewhere across the planet.
Network Interface Card
The NIC is just that: the interface between your
workstation/desktop and the network to which you connect.
When installed into an expansion slot on a motherboard,
or inserted into the PCMCIA slot on a laptop, it is the
electrical, electronic, and physical connection between a
PC and a network. A NIC is designed for a particular type
of network—-Ethernet or Token Ring—-so that it knows how
to communicate.
The one thing you should remember about the NIC card is
that every single NIC has a unique identification tag
called the MAC address. The Media Access Control address
comes from the manufacturer and cannot be changed. It is
used to identify the particular node, aka your workstation,
on the network.
Cabling
There are basically 3 types of cables used in
internetworking:
Coaxial (coax)
Twisted-pair
Fiber Optic
Coax cables have a copper wire in the centre surrounded by
an insulator, shield, and a plastic jacket of either PVC or
Teflon. There are 2 main types of coaxial cables: Thicknet
and Thinnet. Thicknet (Thick Ethernet) is thick (DUH!
almost half an inch in diameter) and inflexible. It can
carry a signal 500 meters in a single segment, and is also
known at 10base5: the first Ethernet cabling system.
Thinnet (Thin Ethernet or 10base2), in contrast, is
thinner, more flexible and can carry a signal 185 meters in
one segment. Coax cables connect to a BNC connector.
Twisted-pair cables have several sets of wires twisted, in
pairs, inside a jacket. They can be shielded, called STP
(shielded twisted pair) or UTP (unshielded twisted pair).
STP is most often used in a token ring network, whereas UTP
is found on most star networks. The pairs of wires within
the cable are twisted to reduce EMI or crosstalk. When you
vary the rate of twists, you reduce the amount of crosstalk
even further. UTP is separated into categories, 1 to 6.
Category 1 has two twisted-pairs and is rated for voice
communications only. Category 3 has four twisted-pairs with
about 3 twists per foot that enables transmission rates
around 10Mbps, in theory. Category 5 cables-—the most
common category of UTP—-have 4 pairs of wires (8 wires all
together) and are rated for transmission rates of 100 Mbps.
Cat5e is the same as Cat5, except that the rate of twists
varies. Category 6 (the most recent standard) also has 4
pairs of wires, but is rated for 1000 Mbps. Twisted pair
cables connect to an RJ-45 connector, a larger version of
your RJ-11 (registered jack) for your telephone.
Fiber Optic cables are made of glass and transmit signals
with light. These cables are expensive and require special
training to install them. There is no EMI with fiber optic
cables,...
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