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1. Network Reference
Models
LECTURE (2)

2. Network Reference Models
Definition:
A framework (guideline) for network implementation and
troubleshooting.
Divides complex functions into simpler components.
Importance of reference model:
◦ Provides a standard for hardware development
◦ Allows for modular software development
◦ Speed development of new technology
◦ Better understanding of data transfer
Reference model types :
OSI (Open System Interconnection ).
TCP/IP (Transmission Control Protocol (TCP) and the
Internet Protocol (IP). DOD Model (U.S. Department of
Defense). )

3. OSI reference model
Although the protocols associated with the OSI model
are not used any more, the model itself is actually quite
general and still valid, and the features discussed at
each layer are still very important.
The OSI isn’t a physical model, though. Rather, it’s a
set of guidelines that application developers can use to
create and implement applications that run on a
network.

4. TCP/IP model
The TCP/IP model has the opposite properties: the
model itself is not of much use but the protocols are
widely used.

5. Advantages of R.M
It divides the network communication process into smaller and
simpler components, thus aiding component development, design,
and troubleshooting.
It allows multiple-vendor development through standardization of
network components.
It encourages industry standardization by defining what functions
occur at each layer of the model.
It allows various types of network hardware and software to
communicate.
It prevents changes in one layer from affecting other layers, so it does
not hamper development.

6. OSI Reference Model
OSI: Open Systems Interconnection
The OSI model is the primary architectural model for
networks.
It describes how data and network information are
communicated from an application on one computer,
through the network media, to an application on another
computer.
The model was defined by the International Organization
for Standardization (ISO)
The OSI reference model breaks this approach into layers.

7. The principlesof designof 7 layers
 The principles that were applied to arrive at the seven
layers can be briefly summarized as follows:
1. A layer should be created where a different
abstraction is needed.
2. Each layer should perform a well-defined function.
3. The function of each layer should be chosen with an
eye toward defining internationally standardized
protocols.

8. Cont. The principles of design of 7layers
4. The layer boundaries should be chosen to minimize
the information flow across the interfaces.
5. The number of layers should be large enough that
distinct functions need not be thrown together in the
same layer out of necessity and small enough that the
architecture does not become unwieldy.

10. OSI model

11. OSI Model
The OSI seven different layers can be divided into two
groups.
The top three layers define how the applications
within the end stations will communicate with each
other and with users.
The bottom four layers define how data is transmitted
end-to-end.

12. OSI Reference Model (cont.)

13. Layer 7 - The ApplicationLayer
•It’s the Sw on our pcs that is
used to represent a user
interface to the network & so
aids the user to make
applications.
Examples:
•Email (SMTP,POP3)
•Web browsers (HTTP)
•FTP
•Telnet
7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data Link
1 Physical

14. Layer 6 - The PresentationLayer
This layer is responsible for
presenting the data in the
proper format .
Examples:
ASCII, AVI,JPG,….
7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data Link
1 Physical

15. Layer 5 - The Session Layer
•Ensure that all information
required for opening a session is
available.
•Give orders for: establishment,
management, and termination
of the session.
7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data Link
1 Physical

16. Layer 4 - The Transport Layer
• Responsible for actual mechanism of:
1. Establishment of connection.
2. Management of connection:
2.1) segmentation.
2.2) sequencing.
2.3) end-to-end check.
2.4) error detection &correction.
2.5) flow control.
3. Termination of connection.
Examples:
• TCP (transmission control protocol).
• UDP (User Datagram Protocol).
7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data Link
1 Physical

17. Layer 3 - The NetworkLayer
Responsible for:
1. End-to-end delivery.
2. Logical addressing .
EX: IPv4,IPv6,IPX,APPLETALK
3. Routing (choose the best path
to destination.)
EX: RIP,OSPF,IS-IS,EIGRP
Devices : Router
7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data Link
1 Physical

18. Layer 2 - The Data Link Layer
Responsible for:
1. Hop-to hop data delivery.
2. Hop-to-hop addressing (MAC
Address in Ethernet).
3. Hop-to-hop error detection
4. Hop-to-hop flow control.
5. Data is framed
6. Devices are:
Bridges.
Switches.
Wireless access points (WAPs).
7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data Link
1 Physical

19. Layer 1 - The Physical Layer
It’s responsible for all Physical
properties of the network :
1. Cable length.
2. Cable type.
3. Bit rate send / receive.
4. Voltage levels.
5. H/W interface types. devices
NIC.
Repeaters.
7 Application
6 Presentation
5 Session
4 Transport
3 Network
2 Data Link
1 Physical

20. Draw the OSI model indicating the name of each layer in
the model ?

22. The TCP/IP Reference Model
TCP/IP (Transmission Control Protocol (TCP) and the
Internet Protocol (IP).
It is used in the grandparent of all wide area computer
networks, the ARPANET (Advanced Research Projects
Agency Network) , and its successor, the worldwide
Internet.
it is useful to mention a few key aspects of it now. The
ARPANET was a research network sponsored by the DoD
(U.S. Department of Defense).
It eventually connected hundreds of universities and
government installations, using leased telephone lines.

23. The TCP/IP Reference Model
It has the ability to connect multiple networks in a
seamless way was one of the major design goals.
This architecture later became known as the TCP/IP
Reference Model
another major goal was that the network be able to
survive loss of subnet hardware, without existing
conversations being broken off

24. TCP / IP
Benefits of TCP /IP
 TCP/IP is a widely published open standard and is
completely independent of any hardware or software
manufacturer.
 TCP/IP can send data between different computer
systems running completely different operating systems,
from small PCs all the way to mainframes and everything
everything in between.
TCP/IP is separated from the underlying hardware and
will run over Ethernet, Token Ring, and X.25 networks, to
name a few, and even over dial-up telephone lines.

25. TCP/IP is a routable protocol, which means it can send
datagrams over a specific route, thus reducing traffic on
other parts of the network.
 TCP/IP has reliable and efficient data-delivery
mechanisms.
 TCP/IP uses a common addressing scheme. Therefore,
any system can address any other system, even in a
network as large as the Internet

26. protocols

27. some abbreviations
(DNS) Domain Name System
UDP (User Datagram Protocol)
(SMTP) electronic mail
TCP (Transmission Control Protocol),
(FTP) file transfer protocol ,

28. some abbreviations
 PDU (Protocol Data Unit).
IP (Internet Protocol),
ICMP (Internet Control Message Protocol)
HTTP (HyperText Transfer Protocol),
RTP (Real-time Transport Protocol)
SONET (Synchronous Optical NETwork).
DSL, short for Digital Subscriber Line

29. Layers with TCP/IP and OSI Model
Compare OSI and TCP/IP model
data
segment
packet
frame
bits

30. A completecommunicationprocess
includes these steps:
1. Creation of data at the application layer of the
originating source end device.
2. Segmentation and encapsulation of data as it
passes down the protocol stack in the source end
device.
3. Generation of the data onto the media at the
network access layer of the stack.

31. Cont. A complete communication process
4. Transportation of the data through the
internetwork, which consists of media and any
intermediary devices.
5. Reception of the data at the network access layer of
the destination end device.
6. Decapsulation and reassembly of the data as it
passes up the stack in the destination device.
7. Passing this data to the destination application at
the Application layer of the destination end device.

32. Encapsulation
Encapsulation process is the addition of information to the
data to be transmitted over the network at each level .
Five steps to encapsulate data
 1- Build the data.
As a user sends an e-mail message, its alphanumeric
characters are converted to data that can travel across the
internetwork.
 2- Package the data for end-to-end transport.
The data is packaged for internetwork transport. By using
segments, the transport function ensures that the message hosts
at both ends of the e-mail system can reliably communicate.

33. Encapsulation
3 - Add the network IP address to the header.
The data is put into a packet or datagram that contains
a packet header with source and destination logical
addresses. These addresses help network devices send
the packets across the network along a chosen path.
backbone, and go out a WAN link until it reaches its
destination on another remote LAN

34. Encapsulation
 4-Add the data link layer header and trailer.
Each network device must put the packet into a frame. The frame
allows connection to the next directly-connected network device
on the link. Each device in the chosen network path requires
framing in order for it to connect to the next device.
 5- Convert to bits for transmission.
The frame must be converted into a pattern of 1’s and 0’s (bits)
for transmission on the medium. A clocking function enables the
devices to distinguish these bits as they travel across the medium.
The medium on the physical internetwork can vary along the path
used. For example, the e-mail message can originate on a LAN,
cross a campus backbone, and go out a WAN link until it reaches
its destination on another remote LAN

35. Encapsulation
Server
Data
HTTP
Header
TCP
Header
IP Header
Data Link
Header
Data Link
Trailer
HTTP Data
Encapsulation – Process
of adding control
information as it passes
down through the layered
model.
trailer

36. TheCommunicationProcess-Decapsulation
Data
HTTP
Header
TCP
Header
IP Header
Data Link
Header
Data Link
Trailer
Client
HTTP Data
trailer

37. TheCommunication
Process
Protocol Data Unit (PDU) –
The form that a piece of data takes at any layer.
At each stage of the process, a PDU has a different name to reflect its new
appearance.
PDUs are named according to the protocols of the TCP/IP suite.
◦ Data - The general term for the PDU used at the Application layer
◦ Segment - Transport Layer PDU
◦ Packet - Internetwork Layer PDU
◦ Frame - Network Access Layer PDU
◦ Bits - A PDU used when physically transmitting data over the medium

38. Addressing and Naming Schemes
Explain how labels in encapsulation headers are used to
manage communication in data networks
Processes communicating over an internet need
addresses for exchanging data between them as follows:


39. AddressingandNamingSchemes
Mac address: Defined by data link layer [identify hosts
in LANS].
 IP address: Defined by Network layer [define network
and host]
 Port address : Defined by transport layer [identify
process]

40. Difference Between IP & MAC addresses
MAC A
IP: 1.1.1.1
MAC B
IP: 1.1.1.2
MAC C
IP: 1.1.1.3
MAC D
IP: 2.2.2.1
MAC E
IP: 2.2.2.2

41. Report
What are the Differences between OSI Reference Model
and TCP/IP model ( 10 differences at least)
What are the Differences between IP address
and MAC address (10 differences at least )

42. What is the Address on myEthernet NIC?

43. Network devices capabilities