1 introduction-to-computer-networking

Introduction to computer networking

Objective:
To be acquainted with:
 The definitions of networking
 Network topology
 Network peripherals, hardware and software

Definitions

1.1 Network Definition
 A network can be defined as two or more
computers connected together in such a way
that they can share resources.

 The purpose of a network is to share
resources.

Definitions (cont..)

A resource may be:
 A file
 A folder
 A printer
 A disk drive
 Or just about anything else that exists on
a computer.

Definitions (cont..)
A network is simply a collection of computers or
other hardware devices that are connected
together, either physically or logically, using
special hardware and software, to allow them to
exchange information and cooperate. Networking
is the term that describes the processes involved
in designing, implementing, upgrading, managing
and otherwise working with networks and network
technologies.

Advantages of networking
 Connectivity and Communication
 Data Sharing
 Hardware Sharing
 Internet Access
 Internet Access Sharing
 Data Security and Management
 Performance Enhancement and Balancing
 Entertainment

The Disadvantages (Costs) of Networking

 Network Hardware, Software and Setup
Costs
 Hardware and Software Management and
Administration Costs
 Undesirable Sharing
 Illegal or Undesirable Behavior
 Data Security Concerns

Fundamental Network Classifications

Local Area Networks (LANs):
 A local area network (LAN) is a computer network covering a small geographic area, like a
home, office, or group of buildings

Wide Area Networks (WANs):
 Wide Area Network (WAN) is a computer network that covers a broad area (i.e., any
network whose communications links cross metropolitan, regional, or national boundaries).
Or, less formally, a network that uses routers and public communications links
 The largest and most well-known example of a WAN is the Internet.
 WANs are used to connect LANs and other types of networks together, so that users and
computers in one location can communicate with users and computers in other locations

Metropolitan Area Network (MAN):
o A metropolitan area network (MAN) is a network that interconnects users with computer
resources in a geographic area or region larger than that covered by even a large local area
network (LAN) but smaller than the area covered by a wide area network (WAN). The term is
applied to the interconnection of networks in a city into a single larger network (which may
then also offer efficient connection to a wide area network). It is also used to mean the
interconnection of several local area networks by bridging them with backbone lines. The
latter usage is also sometimes referred to as a campus network.

Fundamental Network Classifications (cont)

The Local Network (LAN)
Client Client

Client Client

Client Client


 Wide Area Network


Metropolitan Area Network (MAN)

Intranet and Internet Specifications
 Intranet: An intranet is a private network that is contained within
an enterprise. It may consist of many interlinked local area
networks and also use leased lines in the wide area network.
 An intranet uses TCP/IP, HTTP, and other Internet protocols and
in general looks like a private version of the Internet. With
tunneling, companies can send private messages through the
public network, using the public network with special
encryption/decryption and other security safeguards to connect
one part of their intranet to another.
 Internet: is a worldwide system of computer networks - a network
of networks in which users at any one computer can, if they have
permission, get information from any other computer (and
sometimes talk directly to users at other computers).

Client and Server computer role in
networking
 Server computer is a core component of the network,
providing a link to the resources necessary to perform
any task.
 A server computer provides a link to the resources
necessary to perform any task.
 The link it provides could be to a resource existing on
the server itself or a resource on a client computer.
 Client computers normally request and receive
information over the network client. Client computers
also depends primarily on the central server for
processing activities

Peer-to peer network
 A peer-to-peer network is a network where the
computers act as both workstations and servers.
 great for small, simple, and inexpensive networks.
 In a strict peer-to-peer networking setup, every
computer is an equal, a peer in the network.
 Each machine can have resources that are shared
with any other machine.
 There is no assigned role for any particular device,
and each of the devices usually runs similar software.
Any device can and will send requests to any other.

Client/Server Networking

 Inthis design, a small number of
computers are designated as centralized
servers and given the task of providing
services to a larger number of user
machines called clients

Client/Server Networking (cont..)

Network topology

A topology is a way of “laying out” the
network. Topologies can be either
physical or logical.
 Physical topologies describe how the
cables are run.
 Logical topologies describe how the
network messages travel

Network topology (cont.)

 Bus (can be both logical and physical)
 Star (physical only)
 Ring (can be both logical and physical)
 Mesh (can be both logical and physical)

Bus
 A bus is the simplest physical topology. It consists of a
single cable that runs to every workstation
 This topology uses the least amount of cabling, but
also covers the shortest amount of distance.
 Each computer shares the same data and address
path. With a logical bus topology, messages pass
through the trunk, and each workstation checks to see
if the message is addressed to itself. If the address of
the message matches the workstation’s address, the
network adapter copies the message to the card’s on-
board memory.


 it is difficult to add a workstation
 have to completely reroute the cable and
possibly run two additional lengths of it.
 if any one of the cables breaks, the
entire network is disrupted. Therefore, it
is very expensive to maintain.


 Bus topology

Star Topology
 A physical star topology branches each network
device off a central device called a hub, making it very
easy to add a new workstation.
 Also, if any workstation goes down it does not affect
the entire network. (But, as you might expect, if the
central device goes down, the entire network goes
down.)
 Some types of Ethernet and ARCNet use a physical
star topology. Figure 8.7 gives an example of the
organization of the star network.

 Star topologies are easy to install. A
cable is run from each workstation to the
hub. The hub is placed in a central
location in the office.
 Star topologies are more expensive to
install than bus networks, because there
are several more cables that need to be
installed, plus the cost of the hubs that
are needed.


 Star Topology


Ring
 Each computer connects to two other
computers, joining them in a circle creating a
unidirectional path where messages move
workstation to workstation.
 Each entity participating in the ring reads a
message, then regenerates it and hands it to
its neighbor on a different network cable.

 The ring makes it difficult to add new
computers.
 Unlike a star topology network, the ring
topology network will go down if one
entity is removed from the ring.
 Physical ring topology systems don’t
exist much anymore, mainly because the
hardware involved was fairly expensive
and the fault tolerance was very low.


 Ring Topology

Mesh
 The mesh topology is the simplest logical topology in terms of
data flow, but it is the most complex in terms of physical design.
 In this physical topology, each device is connected to every other
device
 This topology is rarely found in LANs, mainly because of the
complexity of the cabling.
 If there are x computers, there will be (x × (x–1)) ÷ 2 cables in the
network. For example, if you have five computers in a mesh
network, it will use 5 × (5 – 1) ÷ 2, which equals 10 cables. This
complexity is compounded when you add another workstation.
 For example, your five-computer, 10-cable network will jump to
15 cables just by adding one more computer. Imagine how the
person doing the cabling would feel if you told them you had to
cable 50 computers in a mesh network—they’d have to come up
with 50 × (50 – 1) ÷ 2 = 1225 cables!

 Because of its design, the physical mesh topology is very
expensive to install and maintain.
 Cables must be run from each device to every other device. The
advantage you gain from it is its high fault tolerance.
 With a logical mesh topology, however, there will always be a
way of getting the data from source to destination.
 It may not be able to take the direct route, but it can take an
alternate, indirect route. It is for this reason that the mesh
topology is still found in WANs to connect multiple sites across
WAN links. It uses devices called routers to search multiple
routes through the mesh and determine the best path.
 However, the mesh topology does become inefficient with five or
more entities.


 Mesh Topology

 Advantages and Disadvantages of Network Topologies

Topology Advantages Disadvantages

Bus Cheap. Easy to install. Difficult to reconfigure.
Break in bus disables
entire network.

Star Cheap. Easy to install. More expensive than bus.
Easy to reconfigure.
Fault tolerant.

Ring Efficient. Easy to install. Reconfiguration difficult.
Very expensive.

Mesh Simplest. Most fault tolerant. Reconfiguration extremely difficult.
Extremely expensive.
Very complex.

Hardware, Software and Networks
Peripherals (device)
 Network Interface Card (NIC)
 Repeater
 Hub
 Bridge
 Routers
 Switch

Hardware, Software and Networks Peripherals (cont.)

Network Interface Card (NIC)
 NIC provides the physical interface between computer and
cabling.
 It prepares data, sends data, and controls the flow of data. It can
also receive and translate data into bytes for the CPU to
understand.
 The following factors should be taken into consideration when
choosing a NIC:
1. - Preparing data
2. - Sending and controlling data
3. - Configuration
4. - Drivers
5. - Compatibility
6. - Performance

Preparing Data

 In the computer, data moves along buses in parallel,
as on a four-lane interstate highway. But on a network
cable, data travels in a single stream, as on a one lane
highway. This difference can cause problems
transmitting and receiving data, because the paths
traveled are not the same.
 It is the NIC’s job to translate the data from the
computer into signals that can flow easily along the
cable.
 It does this by translating digital signals into electrical
signals (and in the case of fiber-optic NICs, to optical
signals).

Sending and Controlling Data

 For two computers to send and receive data, the cards must
agree on several things. These include the following:
- The maximum size of the data frames
- The amount of data sent before giving
confirmation
- The time needed between transmissions
- The amount of time needed to wait before sending
confirmation
- The amount of data a card can hold
- The speed at which data transmits
 In order to successfully send data on the network, you need to
make sure the network cards are of the same type and they are
connected to the same piece of cable.

Configuration

 The NIC’s configuration includes things like a
manufacturer’s hardware address, IRQ
address, Base I/O port address, and base
memory address. Some may also use DMA
channels to offer better performance.
 Each card must have a unique hardware
address. If two cards have the same hardware
addresses, neither one of them will be able to
communicate.

Drivers

 For the computer to use the network
interface card, it is very important to
install the proper device drivers.
 These drivers communicate directly with
the network redirector and adapter. They
operate in the Media Access Control
sublayer of the Data Link layer of the
OSI model.

Compatibility

 When choosing a NIC, use one that fits
the bus type of your PC. If you have
more than one type of bus in your PC
(for example, a combination ISA/PCI),
use an NIC that fits into the fastest type
(the PCI, in this case).
 This is especially important in servers,
as the NIC can very quickly become a
bottleneck if this guideline isn’t followed.

Performance

 The most important goal of the network
adapter card is to optimize network
performance and minimize the amount
of time needed to transfer data packets
across the network.
 There are several ways of doing this,
including assigning a DMA channel, use
of a shared memory adapter, and
deciding to allow bus mastering.

Repeaters

 Repeaters are very simple devices. They allow a cabling system
to extend beyond its maximum allowed length by amplifying the
network voltages so they travel farther.
 Repeaters are nothing more than amplifiers and, as such, are
very inexpensive.
 Repeaters can only be used to regenerate signals between
similar network segments.
 For example, we can extend an Ethernet 10Base2 network to 400
meters with a repeater. But can’t connect an Ethernet and Token
Ring network together with one.
 The main disadvantage to repeaters is that they just amplify
signals. These signals not only include the network signals, but
any noise on the wire as well.
 Eventually, if you use enough repeaters, you could possibly
drown out the signal with the amplified noise. For this reason,
repeaters are used only as a temporary fix.

Repeaters

Hubs

 Hubs are devices used to link several computers
together.
 They repeat any signal that comes in on one port and
copy it to the other ports (a process that is also called
broadcasting).
 There are two types of hubs: active and passive.
 Passive hubs simply connect all ports together
electrically and are usually not powered.
 Active hubs use electronics to amplify and clean up
the signal before it is broadcast to the other ports.
 In the category of active hubs, there is also a class
called “intelligent” hubs, which are hubs that can be
remotely managed on the network.

Hubs

Bridges

 They join similar topologies and are used to divide network
segments.
 For example, with 200 people on one Ethernet segment, the
performance will be mediocre, because of the design of Ethernet
and the number of workstations that are fighting to transmit. If you
divide the segment into two segments of 100 workstations each,
the traffic will be much lower on either side and performance will
increase.
 If it is aware of the destination address, it is able to forward
packets; otherwise a bridge will forward the packets to all
segments. They are more intelligent than repeaters but are
unable to move data across multiple networks simultaneously.
 Unlike repeaters, bridges can filter out noise.
 The main disadvantage to bridges is that they can’t connect
dissimilar network types or perform intelligent path selection. For
that function, you would need a router.

Bridges

Routers

 Routers are highly intelligent devices that connect multiple
network types and determine the best path for sending data.
 The advantage of using a router over a bridge is that routers can
determine the best path that data can take to get to its
destination.
 Like bridges, they can segment large networks and can filter out
noise.
 However, they are slower than bridges because they are more
intelligent devices; as such, they analyze every packet, causing
packet-forwarding delays. Because of this intelligence, they are
also more expensive.
 Routers are normally used to connect one LAN to another.
 Typically, when a WAN is set up, there will be at least two routers
used.

Routers

Switch

 A network switch is a computer networking device that connects network
segments.
 Low-end network switches appear nearly identical to network hubs, but a switch
contains more "intelligence" (and a slightly higher price tag) than a network hub.
 Network switches are capable of inspecting data packets as they are received,
determining the source and destination device of that packet, and forwarding it
appropriately.
 By delivering each message only to the connected device it was intended for, a
network switch conserves network bandwidth and offers generally better
performance than a hub.
 A vital difference between a hub and a switch is that all the nodes connected to
a hub share the bandwidth among themselves, while a device connected to a
switch port has the full bandwidth all to itself.
 For example, if 10 nodes are communicating using a hub on a 10-Mbps network,
then each node may only get a portion of the 10 Mbps if other nodes on the hub
want to communicate as well. .
 But with a switch, each node could possibly communicate at the full 10 Mbps.

Switch

LAB1
 Connect 2 buildings 3 storey high with a distance of
500m between each building.
 Each floor is occupied by the Finance Department,
Administration Department and Computing
Department.
 Your report should have the following items. Anything
extra is encouraged.
a. Introduction
b. Network Diagrams
c. Devices that will be used.
 You are required to use MS Visio to draw the Network
Diagrams.

1 introduction-to-computer-networking

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