A computer network allows devices to communicate with each other over a transmission medium. There are two main types of networks: local area networks (LANs) which connect devices within a limited geographic area like an office, and wide area networks (WANs) which interconnect multiple LANs across an unlimited geographic area. Common topologies for LANs include bus, star, and ring configurations. Network devices like switches and routers allow communication within and between LANs and WANs.

1. Networking
What is a Computer Networking ?
A networking is a collection of computers, printers,
routers, switches and other devices that are able to
communicate with each other over some transmission
media
Advantages of Networking
1.
2.
3.
4.
Resource Sharing
High Reliability
Communication Media
High Speed
Types of Networks
 Local Area Networks (LAN)
 Wide Area Networks (WANs)

2. Local Area Networks (LAN)
A Local Area Network (LAN)
is a group of computers and
network
communicating
devices within a limited
geographic area, such as an
office building.
Wide Area Networks (WAN)
A wide Area Networking (WAN)
interconnects LANs. It is not
restricted to a particular
geographic area and may be
interconnected around the world.
No third party involvement
here
High data transfer speeds
Generally less expensive
technologies
Limited geographic area
Third party network is involved.
Multiple interconnected LANs
More sophistificated to
implement than LANs
Exists in an unlimited
geographic area
Less error resistance due to
transmission travel distances

3. Features of LAN
•
•
•
•
•
•
•
Standard PC Hardware
Resource Sharing
Common Applications
File Sharing
Data Security
Fault Tolerance
Centralized Security

4. Client Server

5. Peer to Peer Network

6. Peer to Peer Network
In peer-to-peer networks, each computer is
considered as a server as well as a client and
holds its own accounts database. Each
computer can share resources that it owns, like
files, CD-ROM drives, printers, modems and
fax machines.
Eg. Windows workgroups.

7. Advantages of Peer to Peer Network
• Security responsibility of each workstation
• Each station runs same software
• Each computer has its own accounts
database
• Cheap and easy to set up for small
groups
• No centralized server required

8. Open Systems Interconnect (OSI) model
·
·
·
·
·
·
·
Application
Presentation
Session
Transport
Network
Data link
Physical

10. Layer 1 - Physical Layer Provides
•
•
•
•
Data Encoding
Physical Medium Attachment
Physical Medium Transmission
Relates the electrical, optical mechanical and
functional interfaces to the cable

11. Layer 2 – Data link Layer
•
•
•
•
•
•
•
Link Establishment and Termination
Frame Traffic Control
Frame Sequencing
Frame Acknowledgment
Frame Delimiting
Frame Error Checking
Media Access Management
The data link layer consists of two sub layers:
1. LLC (logical link control) layer
2. MAC (Media Access Control) layer

12. Layer 3 -Network layer
1. Defines logical addressing
2. Routing occurs at this layer
3. Routing: routes frames among
networks.
4. Subnet traffic control
5. Frame fragmentation
6. Logical-physical address mapping

13. Layer 4 - Transport layer provides:
•
•
•
•
•
•
Message segmentation
Message acknowledgment
Message traffic control
Session multiplexing
Responsible for packet creation.
Gateways operate at this layer.

14. Layer 5 - Session Layer
1. Session establishment
2. Session support
3. The session layer establishes,
manages, maintains and terminates
communication channels between
software programs on network nodes.

15. Layer 6 - Presentation layer provides
•
•
•
•
Character code translation
Data conversion
Data compression
Data encryption

16. Layer 7 - Application layer
•
•
•
•
•
•
•
•
•
Resource sharing and device redirection
Remote file access
Remote printer access
Inter-process communication
Network management
Directory services
Electronic messaging (such as mail)
Network virtual terminals
Serves as a window for applications to
access
• network services

17. Topology of LAN
In a bus topology :
 a single cable connects each workstation in a linear,
daisy-chained fashion
 signals are broadcasted to all stations, but stations only
act on the frames addressed to them

18. BUS TOPOLOGY
Advantages
•
•
•
•
•
Easy to implement
•
Low Cost
Easy to connect a
computer or peripheral •
to a linear bus
Requires less cable
length than a star top
•
Disadvantages
Entire
network
shuts
down if there is a break
in the main cable
Terminators are required
at both ends of the
backbone cable.
Difficult to identify the
problem if the entire
network shuts down

19. In a ring topology :
 Unidirectional links connect the transmit side of one device to
the receive side of another device.
 Devices transmit frames to the next device (downstream
member) in the ring

20. Star Topology
In a Star topology, each station is connected to a central hub or
concentrator that functions as a multi-port repeater. Each station
broadcasts to all of the devices connected to the hub. Physical LAN
topologies are usually characterized as either bus or ring

21. STAR TOPOLOGY
Advantages
Disadvantages
•
•
•
•
•
•
Easy Network
•
management
Initial installation of star
networks is easier
•
Network reliability is high.
Easy to install and wire.
No disruptions to the
•
network then connecting or
removing devices.
Easy to detect faults and
to remove parts
Requires more cable
length than a linear
topology.
If the hub or concentrator
fails, nodes attached
are disabled.
More expensive than
linear bus topologies
because of the cost of
the concentrators.

23. TREE TOPOLOGY
Advantages
Disadvantages
•
•
Point-to-point wiring for
individual segments.
Supported by several
hardware and software
venders
•
•
•
Overall length of each
segment is limited by the
type of cabling used.
If the backbone line
breaks, the entire
segment goes down.
More difficult to configure
and wire than other
topologies.

25. Local Area Network Cabling
The earliest LANs used coaxial cables. Over time, the
twisted Pair cables used in telephone systems were
improved to carry higher frequencies and support LAN
traffic. More recently, fibre optic cables have emerged as a
high speed cabling option.
Local Area Networks use four types of cables :
 Coaxial
 Unshielded Twisted Pair (UTP)
 Shielded Twisted Pair (STP)
 Fibre Optics

26. Coaxial Cables
BNC Connector

27. Unshielded Twisted Pair

28. Unshielded Twisted Pair
Unshielded twisted pair (UTP) cable is used for both LANs and telephone
systems. UTP cables are composed of four colour-coded pairs of copper
conductors twisted around each other. An outer jacket provides protection
and keeps the pairs in alignment. UTP cable connects to devices via 8 pin
modular connectors called RJ – 45 plugs. All LAN protocals can operate over
UTP. Most modern LAN devices are equipped with RJ-45 Jacks

29. Shielded Twisted Pair (STP)
STP cable is also used for Data Networks. It
originated with IBM’s Token – Ring Networks.
It shielding allow greater tolerances for
protection from EMI interference, such as
from fluorescent light fixtures and electronic
motors.

30. Fibre Optics
Fibre optics cables are the latest development in cabling
technology. They are constructed from optical glass.
There is a central glass filament, called the core, and
surrounding layers of cladding, buffer coatings,
strengthening materials and an outer jacket.
Information is transmitted by wavelengths of light. This
is accomplished through devices that convert electrical
signals into rapid pulses of either LED or Laser light.
Advantages of Fibre Optics
 High bandwidth capacity (many giga bits per second)
 Longer distances between devices (from 2 to over 60
Kilometers)
 immunity to electromagnetic interferences

32. Fibre optic cables are widely used in WANs for both voice
and data communications. The primary barrier to their
widespread use in LANs is the cost of electronics.

33. Physical
Topology
Common
Cable
Common
Protocol
Linear Bus
Twisted Pair
Coaxial
Fiber
Ethernet
Local Talk
Star
Twisted Pair
Fiber
Ethernet
Local Talk
Star-Wired
Ring
Twisted Pair
Token Ring
Tree
Twisted Pair
Coaxial
Fiber
Ethernet

34. LAN Infrastructure Devices
 Repeaters
 Bridges
 Hubs
 Switches
 Routers

35. Repeaters
Repeaters, located within physical layer of
a network, regenerate and propagate
signals from one to another. They do not
change any information being transmitted,
and they can not filter any information.
Repeaters help to extend the distances of
networks by boosting weak signals.

36. Bridges
Bridges are intelligent repeaters. They regenerate
transmitted signals, but unlike repeaters, they
can also determine destinations.

37. Hubs
Hubs connect all computer LAN connections into
one device. They are nothing more than multiport
repeaters. Hubs cannot determine destinations.
They merely transmit to every line attached in a
half-duplex mode

38. Routers
Routers are a step up from bridges. They
are able to route and filter information to
different networks. Some routers can
automatically detect problems and redirect
information around the problem area.
These are called “Intelligent routers.”

39. Switches
Switches connects all computer LAN
connections, the same as hubs do. The
difference is that switches can run in fullduplex mode and are able to direct and
filter information to and from specific
destinations.

40. WAN infrastructure Devices
ATM Switches
Asynchronous Transfer Mode (ATM)
Switches provide high speed transfer
between both LANs and WANs.

41. Modem
Modems convert digital and analog signals. At
the source, modems convert digital signals to a
form suitable for transmission over analog
communication facilities (Public telephone lines).
At the destination, modems covert the signal back
to a digital format.

42. CSU/DSU (Channel Service Unit /
Data Service Unit)
CSUs / DSUs are similar to modems, however
they send data in digital format across digital
telephone loops. They are usually in a physical
box, but they may come in two separate units.
CSUs or DSUs
Multiplexers
A multiplexer combines multiple signals for
transmission over a single circuit. This allows for
the transfer of various data simultaneously, such
as video, sound, text, etc.

43. Communication Servers
Communication Servers are typically dial in/out
servers that allow users to dial in from remote
locations and attach to the LAN
X.25 / Frame Relay Switches
X.25 band Frame Relay Switches connect private
data over public data circuits using digital signal.
These units are very similar to ATM switches, but
the transfer rate of data is not comparable.

44. Protocols
Communication protocol or network protocol is
the specification of a set of rules for a particular
type of communication.
A commonly used protocols :
 HTTP : Hyper Text Transfer Protocol
 TCP - Transmission Control Protocol
 IP - Internet Protocol
 Ethernet Protocol

45. Other Protocols
 FTP - File Transfer Protocol
 UDP - User datagram protocol
 ICMP - Internet Control Message Protocol
 Telnet Protocol
 IMAP - Internet Message Access Protocol (Previously
called Interactive Mail Access Protocol)
 SMTP - Simple Mail Transfer Protocol
 NTP - Network Time Protocol
 NNTP - Network News Transfer Protocol