1. Unit 1
Network Models
and
Network Examples

2. Unit 1 - Part A
Network Models

3. Alternative definition of Network :
 A network is a combination of hardware and software
that sends data from one location to another.
• Hardware : The hardware consists of the physical
equipment that carries signals from one point of the
network to another.
• Software : The software consists of instruction sets
that make possible the services that we expect from a
network.

4. Sections in Part – A [ Network Models ]
 Layered Tasks
 OSI Model
~ Introduction
~ Layers in OSI Model
 TCP / IP Model
 Addressing

5. 2-1 LAYERED TASKS
Understanding Layered Tasks . . . . . . . . . . .
* We use the concept of layers in our daily life.
* Example :
Consider two friends who communicate through postal mail.
[ i.e. one friend sends a letter to another friend ]

6. Example of sending a letter ( postal mail )

7. Some notable points from the previous example . . . . . .
 Components - The three vital components in any communication
system are : Sender, Receiver and Carrier
 Hierarchy - Layers do exist on both the sites and these layers are
arranged in particular order. In other words, a particular
hierarchy of layers exists. [ Order Matters ! ]
 Services – Each layer at the sending site uses the services of the
layer immediately below it; while each layer at the receiving site
provides the services to the layer immediately above it.

8. 2-2 a) THE OSI MODEL ( Introduction )
What is ISO ?
Established in 1947, the International Standards Organization
(ISO) is a multinational body dedicated to worldwide agreement on
international standards.
What is OSI ?
An ISO standard that covers all aspects of network
communications is the Open Systems Interconnection (OSI)
model. It was first introduced in the late 1970s.
ISO is the organization.
OSI is the model.
Note

9. Topics discussed in this introductory section:
a) Layered Architecture
b) Peer-to-Peer Process
c) Encapsulation

10. a) Layered Architecture

11. b) Peer-to-Peer Processes

12. c) Encapsulation

13. 2-2 b) LAYERS IN THE OSI MODEL
In this section we briefly describe the functions of each
layer in the OSI model.
Topics discussed in this section:
1. Physical Layer
2. Data Link Layer
3. Network Layer
4. Transport Layer
5. Session Layer
6. Presentation Layer
7. Application Layer

14. 1) Physical layer
Note
The physical layer is responsible for movements of
individual bits from one hop (node) to the next.

15. 2) Data link layer
The data link layer is responsible for moving
frames from one hop (node) to the next.
Note

16. Hop-to-hop delivery

17. 3) Network layer
The network layer is responsible for the
delivery of individual packets from
the source host to the destination host.
Note

18. Source-to-destination delivery

19. 4) Transport layer
Note
The transport layer is responsible for the delivery
of a message from one process to another process.

20. Reliable process-to-process delivery of a message

21. 5) Session layer
The session layer is responsible for
dialog control and synchronization.
Note

22. 6) Presentation layer
The presentation layer is responsible for translation,
compression, and encryption.
Note

23. 7) Application layer
The application layer is responsible for
providing services to the user.
Note

24. Summary of layers

25. 2-4 TCP/IP PROTOCOL SUITE
 The original TCP/IP protocol suite was defined as having four layers :
host-to-network, network(internet), transport and application.

26.  The layers in the TCP/IP protocol suite do not exactly match
those in the OSI model.
 However, when TCP/IP is compared to OSI, we can say
that the TCP/IP protocol suite is made of five layers:
physical, data link, network, transport, and application
[next slide . . . . ]

27. Assumed TCP/IP Model ( Internet Model ) in the text book :

28. Overlap of TCP/IP Model (Internet Model) and OSI model

29. 2-5 ADDRESSING
Four levels of addresses are used in an internet employing
the TCP/IP protocols: physical, logical, port, and specific.

30. Relationship of layers and addresses in TCP/IP (Internet Model)

31. 1. Physical Address :
The physical address, also known as the link address,
is the address of the node as defined by its LAN orWAN.
~ It is included in the frame used by the data link layer.
~ It is the lowest-level address.

32. Example to understand physical address
In Figure below 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.

33. 2. Logical Address :
A logical address in the Internet is currently 32-bit
address that can uniquely define a host connected to the
Internet.
~ No two publicly addressed and visible hosts on the Internet
can have the same IP address.
[ Note : IP address is typical example of Logical Address on present day Internet ]

34. Example to understand logical address
Figure in the next slide 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.

36. 3. Port Address :
In TCP / IP model, the label assigned to a process is
called a port address.
~ A port in TCP / IP is 16-bits in length.

37. Example to understand port address
Figure in the next slide 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.

39. Note
The physical addresses change from hop to hop,
but the logical and port addresses usually remain the same.

40. 4. Specific Address :
User-friendly address designed at the level of application
layer is known as specific address.
Example : ~ email address (e.g. baforouzan@gmail.com )
~ website address. ( e.g. www.flipkart.com )