PC Construction and Maintenance Week 7

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27 Οκτ 2013 (πριν από 4 χρόνια και 7 μήνες)

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PC Construction and

Week 7


Introduction to networks

In computing, the term Network generally means
connecting two or more machines together

Networking covers a wide area of computing.

Networking is becoming increasingly important,
even in the home environment

The cost of networking hardware has dropped

Why have networks?

The main reason is to share resources
between computers

Many computers can share a printer

Internet access can be shared amongst a
number of machines

Access to information and resources shared
across a network is often useful in practice

Type of networks

We are concerned with building a small LAN
(Local Area Network) in order to enable file and
printer sharing

Also, a connection to the internet is desirable, for
the download of drivers, patches, BIOS upgrades

The word internet literally means between

The internet is really just a large collection of
networks, themselves networked together

The theory behind networks

Network theory could itself encompass a whole

We are going to explore the tip of the ice
berg of
network theory

We only need to know the key points in order to
have enough knowledge to understand how a
small home or business network functions

There are a just few fundamental facts of
computer networking that interest us

Network Theory

Key Points

All networks are based on a layered model. The
layered model is the theoretical ideal model
of a computer model

Real networks are based on a simplified models of
the theoretical ideal. But always retain the
“layered” quality.

We are interested primarily in TCP/IP networks.
TCP/IP is the protocol that runs the Internet

We need at the very least to know the essential
properties of the layered model in order to
configure and troubleshoot basic networks

layer reference model

7. Application

6. Presentation

5. Session

4. Transport

3. Network

2. Data Link (Hardware Interface)

1. Physical Hardware Connection

ISO layers explained

Physical Layer:

Transmitting data bits. Voltages,
timing factors, cable standards, etc.

Data Link Layer:

Managing basic transmission

Error detection and correction; message

Network Layer:

Addressing and routing of

Transport Layer:

Establish, maintain, and
terminate logical connections. Generating
addresses; breaking packets: eliminating duplicate
packets; flow control.

Session Layer:

Initiating, maintaining, terminate
logical session.

Presentation Layer:

Display, formatting,

Application Layer:


The TCP/IP model

The Physical Layer

For ordinary networks, there are two common
ways of hooking up several computers

One way is to use BNC cabling, provided the
network cards have a BNC connector on them.

The most common way at the present time is to
use UTP (Unshielded Twisted Pair) cable, in
combination with a Hub

BNC based network

All machines are daisy chained together via BNC
cabling and T

There is no need for a hub

If a single wire is disconnected, then the whole
network fails

A terminator is plugged in to both ends of the

This sort of arrangement is known as “BUS

A 10
Mbit BNC network is known as 10

BUS topology (BNC networks)

UTP based network

Several machines are connected together via a hub

Several hubs can be chained together to form a
larger networks

For the simple case of a two
computer network,
you don’t need a hub, you can just use a
‘crossover cable’

UTP based networks are fast and reliable

If one wire is disconnected, then only one
computer is affected. The remaining network still
functions correctly

UTP networks are known as 10BASE
T, or
T, depending on the speed

Star Topology (UTP based

UTP Cable Wiring

UTP Cable Wiring

UTP Cable Wiring Reference

1 White/Orange

2 Orange

3 White/Green

4 Blue

5 White/Blue

6 Green

7 White/Brown

8 Brown

UTP cables

A standard UTP network cable is known as a
straight cable, or a patch cable

If the pairs #2 and #3 are swapped with each
other, then we have a crossover cable

Straight cables are the most common, and are used
to connect a PC to a hub

Crossover cables are used to connect a PC to a PC
(2 PC network) or , a hub to another hub

Receive/Transmit swapping

In the 10
base T case. One twisted pair is for
receiving a signal (Rx), and the other for
transmitting (Tx)

The hub swaps these over internally so that (Tx)
of machine A connects to (Rx) of machine B

Straight cables do not swap Tx and Rx, crossover
cables do.

If the number of “swaps” between the source and
destination machines is odd, then they are wired
correctly, else they will not talk to each other

The datalink layer

The datalink layer deals with transfer of binary
data from one network interface card to another

The dominant datalink protocol used at the current
time in a LAN environment is

Some other datalink protocols are still found on
LANs (e.g. token ring), but these seem to be dying

Because of widespread use of Ethernet
equipment, it is now very cheap

Ethernet Networks

In the Ethernet environment, every network card
on the planet has a unique MAC address

The Media Access Code is used to address
different devices on the network

On a simple network, any device on the network
can address any other device within a given
using its MAC address

Devices cannot address other devices on other
subnets by using a MAC address

This is because the datalink protocol is non

The network layer

IP is the network protocol that drives the Internet
(simply IP=InteRnet Protocol)

It became widely used on UNIX systems to start
off with, but has now spread to virtually every
other operating system

IP is needed to ‘surf the web’

Unlike the datalink layer, IP is a routable protocol
and therefore can be used to build large networks
(e.g. the Internet)

IP architecture

In the IP scheme of things, the network as a whole
is treated as an interconnected set of subnets

Each subnet allows communication within itself
using the aforementioned datalink protocol

Subnet A is connected to Subnet B via a device
known as a router

Each machine on the network (even on the public
internet) must have a unique IP address

IP addresses

IP addresses have a four byte form and are
normally written using a dotted notation

For example

One some networks, static I.P addresses are used,
which means that each machine handles it’s own
IP configuration locally

Some networks employ protocols to allow an IP
address to be assigned dynamically at boot time

Configuring IP under windows

As a test case, we will go through the steps
of configuring IP networking under
windows 95

Firstly, we need to have a network adapter

We need to check using device manager
that a network card is installed

Installing the network card driver

If windows has automatically recognised the card,
then we will see it in device manager

If not, we may need to use the “add hardware

Sometimes, windows can see the card, but doesn’t
know what type it is. In this case, it will show up
as “Unknown device”, next to a question mark

If this happens, remove the unknown device from
device manager and reboot the PC

Windows should then properly detect the card on
the next boot

Installing the network

Once we have the card install correctly, we
need to add the TCP/IP component

click on Network
Neighbourhood (Or
select network) in Control Panel, and then
click on “Add” to add a protocol (You will
need the windows CD in the drive)

The protocol is Microsoft

TCP/IP Parameters

After adding the TCP/IP protocol, we need to
configure the relevant settings to run the machines
on our network

The main setting is IP address (I have reserved a
separate address for each group, written on a list)

The other settings are Subnet Mask,Gateway,
DNS servers and WINS servers

Subnet mask

For our network, the subnet mask is always

The subnet mask defines how we choose to
split our physical subnet into logical subnets

The non
zero (left hand portion) defines the
network part of the address

The zero portion (right hand portion)
defines the host part of the address


For our network, the address of the gateway
(a.k.a the router) is

The router is just a box that bridges the gap
between our network and the outside world

The network could work as a self contained
entity without a router (e.g. as in a home

The router is needed to access the internet

DNS servers

DNS servers are just other computers on our
network that translate things like web
site names
into IP addresses

Without them, we could theoretically still browse
the internet, but we would have to refer to
websites by number, rather than by name

The address of the three DNS servers on our
network are

WINS Servers

WINS servers are used to translate between
Microsoft networking names and IP addresses

We need to configure WINS servers to allow are
machines to use Microsoft network resources such
as shared printers and files

Our WINS servers are and

Completing the configuration

Any other protocols on the system, such as
NetBUI and IPX should be removed on PCs on
our network

After rebooting, the machine should be enabled
for TCP/IP

This can be tested by launching Internet explorer

If that fails, then try “ping” to
bounce a packet of data off the router from the
DOS prompt.

Notes on home networking

In the home environment, there are typically no
WINS or DNS servers available

In that case, it is still possible to run TCP/IP over
the network

Its just that local file configurations are used
instead of network servers

Local file configuration becomes impractical
when working with a large number of machines

Microsoft’s custom protocols may sometimes be
more suited to a small home network (but not for
internet sharing)