A computer network is a collection of connected devices that enables communication and resource sharing, utilizing both wired and wireless connections. Key aspects of network functionality include performance, reliability, and security, as well as the OSI model which categorizes network communication into seven layers. The TCP/IP protocol architecture, established in 1974, serves as the foundation of the Internet and consists of four layers, each playing a critical role in data transmission and addressing.

1. Computer network :
A collection of computing devices that are
connected in various ways in order to
communicate and share resources.
Usually, the connections between computers in
a network are made using physical wires or
cables.
However, some connections are wireless, using
radio waves or infrared signals.

2. Computer network(Continue…)
The generic term node or host refers to any
device on a network.
Data transfer rate : The speed with which
data is moved from one place on a network to
another .
>>Data transfer rate is a key issue in computer
networks.

3. Computer network (Continue…)
Computer networks have opened up an entire
frontier in the world of computing called the
client/server model.

4. Network criteria (Continue…)
A network is selected on the basis of network
criteria. During the network selection, it is
important to consider these criteria for
improving network functionality.
These 3 factors are:
1. Network Performance :
I. Transmit time
II. Response time

5. Network criteria (Continue…)
2. Network Reliability : The reliability of the
network is measured by following factors:
I. Frequency of failure - Determines how
frequently the network fails.
II. Recovery time - It is the time taken by a device
or network to recover from the failure.
III. Catastrophe - Network must be protected from
the disasters such as fire, earthquake and fire.

6. Network criteria (Continue…)
3.Network Security :
I. Security of the network is considered as the
important aspect for improving the network
performance.
II. The network security may be affected due to
viruses and unauthorized access of other
users.

7. OSI Model :
The Open Systems Interconnection model (OSI
Model) is a conceptual model that characterizes
and standardizes the communication functions of
a telecommunication or computing system
without regard of their underlying internal
structure and technology.
The OSI model defines a networking framework
to implement protocols in seven layers.

8. OSI Model : (Continue…)
>> A convenient aid for remembering the OSI layer names is to use
the first letter of each word in the phrase:
All People Seem To Need Data Processing

9. OSI Model : (Continue…)
LAYER 7 – The APPLICATION Layer :
 The top layer of the OSI model.
 Provides a set of interfaces for sending and receiving
applications to gain access to and use network services,
such as: networked file transfer, message handling and
database query processing.
 The application layer is responsible for
providing services to the user.

10. OSI Model : (Continue…)
LAYER 6 – The PRESENTATION Layer :
 Manages data-format information for networked
communications (the network’s translator).
 For outgoing messages, it converts data into a generic
format for network transmission; for incoming messages,
it converts data from the generic network format to a
format that the receiving application can understand.
 This layer is also responsible for certain protocol
conversions, data encryption/decryption, or data
compression/decompression.
 The presentation layer is responsible for translation,
compression, and encryption.

11. OSI Model : (Continue…)
LAYER 5 – The SESSION Layer :
 Enables two networked resources to hold ongoing
communications (called a session) across a network.
 Applications on either end of the session are able to ex hange
data for the duration of the session.
 This layer is:
 Responsible for initiating, maintaining and terminating sessions
 Responsible for security and access control to session
information (via session participant identification).
 The session layer is responsible for dialog
control and synchronization.

12. OSI Model : (Continue…)
LAYER 4 – The TRANSPORT Layer :
 Manages the transmission of data across a network.
 Manages the flow of data between parties by segmenting long
data streams into smaller data chunks (based on allowed
“packet” size for a given transmission medium)
 Reassembles chunks into their original sequence at the
receiving end
 Provides acknowledgements of successful transmissions and
requests resends for packets which arrive with errors.
 The transport layer is responsible for the delivery
of a message from one process to another.

13. OSI Model : (Continue…)
LAYER 3 – The NETWORK Layer :
 Handles addressing messages for delivery, as well as
translating logical network addresses and names into their
physical counterparts.
 Responsible for deciding how to route transmissions between
computers.
 This layer also handles the decisions needed to get data from
one point to the next point along a network path.
 The network layer is responsible for the
delivery of individual packets from
 the source host to the destination host.

14. OSI Model : (Continue…)
LAYER 2 – The DATA LINK Layer :
 Handles special data frames (packets) between the Network
layer and the Physical layer.
 At the receiving end, this layer packages raw data from the
physical layer into data frames for delivery to the Network
layer.
 At the sending end this layer handles conversion of data into
raw formats that can be handled by the Physical Layer.
 The data link layer is responsible for moving
frames from one hop (node) to the next.

15. OSI Model : (Continue…)
LAYER 1 – The PHYSICAL Layer :
 Converts bits into electronic signals for outgoing messages.
 Converts electronic signals into bits for incoming messages.
 This layer manages the interface between the the computer and
the network medium (coax, twisted pair, etc.).
 This layer tells the driver software for the MAU (media
attachment unit, ex. network interface cards (NICs, modems,
etc.)) what needs to be sent across the medium.
 The bottom layer of the OSI model.
 The physical layer is responsible for movements of individual
bits from one hop (node) to the next.

16. TCP/IP Protocol Architecture :
The TCP/IP protocol
suite was first
defined in 1974.
The TCP/IP protocol
suite is the protocol
architecture of the
Internet.
The TCP/IP suite has
four layers :
Application,
Transport, Internet,
and Network
Interface Layer.
Application
Layer
Transport
Layer
Internet
Network
Interface
telnet, ftp, email
TCP, UDP
IP, ICMP, IGMP
Device Drivers

17. TCP/IP Protocol Architecture (Con…)
FTP
program
TCP
IP
Ethernet
Driver
Ethernet
Driver
Ethernet
Driver
IP
FTP
program
TCP
IP
Ethernet
Driver
FTP protocol
TCP protocol
IP protocol IP protocol
Ethernet
protocol
Ethernet
protocol
Example: (File Transfer)

18. TCP/IP Protocol Architecture (Con…)
TCP/IP Protocol Suite :
Application
Layer
Network
Layer
Link Layer
IP
ARP
Hardware
Interface
RARP
Media
ICMP IGMP
Transport
Layer
TCP UDP
User
Process
User
Process
User
Process
User
Process

19. Comparison of OSI Model and TCP/IP
Suite.
Application
Presentation
Session
Transport
Network
Data Link
Physical
Application
Transport
Internetwork
Network
Access
Physical
OSI TCP/IP

20. Addressing in TCP/IP :
Four levels of addresses are used in an internet employing
the TCP/IP protocols: physical, logical, port, and specific
Address.
Addresses in TCP/IP :

21. Addressing in TCP/IP (Continue….)
Relationship of layers and addresses in TCP/IP.

22. Addressing in TCP/IP (Continue….)
Example :
In Figure 2.19 a node with physical address 10
sends a frame to a node with physical address
87. The two nodes are connected by a link (bus
topology LAN). As the figure shows, the
computer with physical address 10 is the
sender, and the computer with physical address
87 is the receiver.

23. Addressing in TCP/IP (Continue….)
Figure 2.19 Physical addresses :

24. Addressing in TCP/IP (Continue….)
Example :
Figure 2.20 shows a part of an internet with two
routers connecting three LANs. Each device
(computer or router) has a pair of addresses
(logical and physical) for each connection. In this
case, each computer is connected to only one link
and therefore has only one pair of addresses. Each
router, however, is connected to three networks
(only two are shown in the figure). So each router
has three pairs of addresses, one for each
connection.

25. Addressing in TCP/IP (Continue….)
Figure 2.20 IP addresses :

26. Addressing in TCP/IP (Continue….)
Figure 2.21 shows two computers communicating via
the Internet. The sending computer is running three
processes at this time with port addresses a, b, and c.
The receiving computer is running two processes at this
time with port addresses j and k. Process a in the
sending computer needs to communicate with process j
in the receiving computer. Note that although physical
addresses change from hop to hop, logical and port
addresses remain the same from the source to
destination.
Example :

27. Addressing in TCP/IP (Continue….)
Figure 2.21 Port addresses