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Networking
Basics
The OSI
Model
The hardest part of
networking is understanding the methodology behind how it
works. There are a group of standards set out for
networking, called the Open Systems Interconnection (OSI)
model.
There are 7 levels to
the OSI model, with each level containing it's own set of
properties. I wouldn't spend much time memorizing the
individual properties of each level. Just try to
memorize the names of the levels themselves and the basic
properties.
Here are the 7
levels;
|
Level (Top
To Bottom) |
Description |
| Application |
Links the
applications used by the client to the network.
(Technically wrong, but good enough for our
purposes.) |
| Presentation |
Responsible
for converting the data from and to the application
layer between the different formats used by the network
and the applications. |
| Session |
Creates and
maintains communication sessions. In order for two
computers to communicate, this layer must tell both
sides that a session is created. |
| Transport |
Breaks down
messages into the appropriate size for the network
type. |
| Network |
Provides
means for networks of different architectures to
communicate. |
| Data Link |
The Data Link
layer is actually split into 2 layers. One
controls how the signaling and data flow will take place
(Link Layer Control, or LLC), and the other maintains
the identification of each node on a network. (Media
Access Control, or MAC) |
| Physical |
This layer is
comprised of all the physical connections, adapters,
wires, terminators, and anything else used to connect
two computers physically. |
**Remember that the
OSI model has a top and a bottom. The Physical layer is
always at the bottom, and the Application layer is always at
the top. The easiest way to remember this is with
another acronym. In this case, try using "Please
Do Not Trust Sales People
Always." You can use your own, and there are many
that float about, but this is the easiest one I've found to
remember.
Network
Terminology
Networks exist for
essentially one reason to share
information. Data exchange and communication are the
basic reasons for every network in existence. (This is
an easy answer to a question you might find that says "What
are networks for?") There are dozens of network specific
terms you will need to know, including;
| Term |
Description |
| Media |
The media is
always the method used to transfer the signals.
The basic media types are copper wire, fiber optic
cable, and radio waves. |
| Nodes |
Every
computer and printer on a network is a
node. |
| Client |
Nodes that
are used by people in order to get data, perform
applications over networks, and use network services are
called Clients. (Also known as
Workstations) |
| Server |
Nodes that
provide services like file storage, application sharing,
and print services are called Servers. Servers can
also be Clients, but Servers generally perform more
functions, provide more services, and have better
equipment installed because they are a focal point on
the network. |
| Protocol |
In order to
communicate, all nodes on a networks must talk a
specific language. Protocols are networking
languages that state rules for how network communication
takes place, including error correction and data packet
size. |
| Topology |
The physical
layout of the network. Most networks come in
either bus, star, or ring topologies, or a mixture of
the three. |
| LAN |
Local Area
Network - A type of network where all the network nodes
are within a specific boundary. LAN's are not
defined as single-room, single-floor, or
single-building. Instead, the relationship between
each node determines if it is a LAN or a WAN. (See
next) |
| WAN |
Wide Area
Network - Networks spread over a wide distance. No
specific distance is stated, but any network that
communicates with other nodes outside of a standard LAN
configuration is a WAN. (To make this confusing, a
WAN is commonly made up of LANs, but you don't require a
LAN to make a WAN. All they'll ask you on the test
is what LAN stands for.) |
| Client/Server |
Client/Server
networking exists when a central node (The Server)
provides services to other nodes. (The Client)
Client/Server networks generally have better security,
central administration, more features (i.e. application
sharing), and easier logons. |
| Peer-To-Peer |
This form of
networking exists when every node in the network
maintains it's own security database, and no central
administration is present. You have to logon to
each node on the network separately, there is no
application sharing, and security is dependant on each
node. These kinds of networks are not suggested
for networks over 10 users. |
| Architecture |
When
referring to a network architecture, you are referring
to whether it is Peer-to-Peer of
Client/Server. |
Topologies
As we stated above,
networks come in different types. Some spread out from a
middle point, some look like a ring, and some are just all in
a row. Even more confusing, some networks are
combinations of these types. Here are the major
topologies you will need to know;
| Topology |
Description |
| Star |
Star networks
are defined by their central connection point.
Each computer on the network connects to a central
server or hub, and all data traffic goes through this
central connection. |
| Ring |
Also called
Token ring, each computer on the network connects only
to it's two next-door neighbors. Traffic travels
around the network in one direction from computer to
computer. The way that data travels is like a
ring, and you must have a complete circle in order to
use this topology. |
| Bus |
These are
essentially straight line networks. All the
computers are hooked up in a line, and data traffic
travels both directions up and down the line.
These are the simplest but least useful networks
available. |
| Hybrid |
A hybrid
network is a network that uses combinations of these
types of topologies. For example, a star network
can have several computers on a bus connection to the
central connection
point. |
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