OSI (open System Interconnection) Developed By ISO (International Organization for Standardization) and I'm rightful Member of that organization, I have separate chair just for myself there. I have relased this Educational presentation with slight misspelled name in order to divert the attention for time being and mislead fools primarily. © Mujmmil Shaikh mujmmil01@gmail.com

2. The Layered Model
© 1999, Cisco Systems, Inc. www.cisco.com

3. Layered Communication
Location A
Ik hou
Message
van
konijnen
L: EN Information
for the
I like Remote
rabbits Translator
Fax #:--- Information
L: EN for the
I like Remote
rabbits Secretary
Source: Tanenbaum, 1996

4. Layered Communication
Location A Location B
Ik hou J’aime
Message
van les lapins
konijnen
L: EN Information L: EN
for the I like
I like Remote
rabbits Translator rabbits
Fax #:---
Fax #:--- Information L: EN
L: EN for the
I like I like
Remote
rabbits Secretary rabbits

5. Layered Communication
Location A Location B
Layers
Ik hou J’aime
van Message
3 les lapins
konijnen
L: EN Information L: EN
I like for the
remote 2 I like
rabbits
rabbits translator
Fax #:---
Fax #:--- Information L: EN
L: EN for the
I like I like
remote
rabbits secretary 1 rabbits

6. Why a Layered Network Model?
7 Application • Reduces complexity (one big
problem to seven smaller ones)
6 Presentation
• Standardizes interfaces
5 Session
• Facilitates modular engineering
4 Transport • Assures interoperable technology
3 Network • Accelerates evolution
2 Data Link • Simplifies teaching and learning
1 Physical

7. Devices Function at Layers
7 Application
6 Presentation
NIC Card
5 Session
4 Transport
3 Network
2 Data Link
1 Physical
Hub

8. Host Layers
}
7 Application
6 Presentation Host layers: Provide accurate
5 Session data delivery between computers
4 Transport
3 Network
2 Data Link
1 Physical

9. Media Layers
}
7 Application
6 Presentation Host layers: Provide accurate
5 Session data delivery between computers
4 Transport
}
3 Network
2 Data Link
Media layers: Control
1 Physical physical delivery of messages over
the network

10. Layer Functions
7 Application Provides network services to application
processes (such as electronic mail, file transfer,
and terminal emulation)

11. Layer Functions
7 Application Network services to applications
6 Presentation Data representation
• Ensures data is readable by
receiving system
• Format of data
• Data structures
• Negotiates data transfer syntax for
application layer

12. Layer Functions
7 Application Network services to applications
6 Presentation Data representation
5 Session Inter-host communication
• Establishes, manages, and terminates
sessions between applications

13. Layer Functions
7 Application Network services to applications
6 Presentation Data representation
5 Session Inter-host communication
4 Transport End-to-end connection reliability
• Concerned with data transport issues
between hosts
• Data transport reliability
• Establishes, maintains, and terminates
virtual circuits
• Fault detection and recovery
• Information flow control

14. Layer Functions
7 Application Network services to applications
6 Presentation Data representation
5 Session Inter-host communication
4 Transport End-to-end connection reliability
3 Network Addresses and best path
• Provides connectivity and path selection
between two end systems
• Domain of routing

15. Layer Functions
7 Application Network services to applications
6 Presentation Data representation
5 Session Inter-host communication
4 Transport End-to-end connection reliability
3 Network Addresses and best path
2 Data Link Access to media
• Provides reliable transfer of data across
media
• Physical addressing, network topology, error
notification, flow control

16. Layer Functions
7 Application Network services to applications
6 Presentation Data representation
5 Session Inter-host communication
4 Transport End-to-end connection reliability
3 Network Addresses and best path
2 Data Link Access to media
1 Physical Binary transmission
• Wires, connectors, voltages, data
rates

17. Peer-to-Peer Communications
Host A Host B
7 Application Application
6 Presentation Presentation
5 Session Session
4 Transport Segments Transport
3 Network Packets Network
2 Data Link Frames Data Link
1 Physical Bits Physical

18. Data Encapsulation
Host A Host B
Application Application
Presentation
Session
Transport
} { Data Presentation
Session
Transport
Network Network
Data Link Data Link
Physical Physical

19. Data Encapsulation
Host A Host B
Application Application
Presentation
Session
Transport
} { Data
Network Data
Header
Presentation
Session
Transport
Network Network
Data Link Data Link
Physical Physical

20. Data Encapsulation
Host A Host B
Application Application
Presentation
Session
Transport
} { Data
Network Data
Header
Presentation
Session
Transport
Network Network
Frame Network Data Frame
Data Link Data Link
Header Header Trailer
Physical Physical

21. Data Encapsulation
Host A Host B
Application Application
Presentation
Session
Transport
} { Data
Network Data
Header
Presentation
Session
Transport
Network Network
Frame Network Data Frame
Data Link Data Link
Header Header Trailer
Physical Physical
0101101010110001

22. Layers 1 & 2:
Physical & Data Link Layers
© 1999, Cisco Systems, Inc. www.cisco.com

23. Physical and Logical Addressing
0000.0c12.3456

24. MAC Address
24 bits 24 bits
Vendor Code Serial Number
0000.0c12. 3456
ROM
RAM
• MAC address is burned into ROM on a network
interface card

25. Layer 3:
Network Layer
© 1999, Cisco Systems, Inc. www.cisco.com

26. Network Layer: Path Determination
Which Path?
Which Path?
• Layer 3 functions to find the best
path through the internetwork

27. Network Layer: Communicate Path
5
2 9
6 8
4
10 11
1 3
7
 Addresses represent the path of media
connections
 Routing helps contain broadcasts

28. Addressing—Network and Node
Network Node
1 1
2.1
2
3 1.2
2 1 1.3 1.1 3.1
3 1
• Network address—Path part used by the router
• Node address—Specific port or device on the network

29. Protocol Addressing Variations
General Network Node
Example 1
1
Network Host
TCP/IP
Example 10. 8.2.48 (Mask 255.0.0.0)
Network Node
Novell IPX
Example 1aceb0b. 0000.0c00.6e25

30. Network Layer
Protocol Operations
X Y
C
C
A
A
 Each router provides its services to support
upper layer functions

31. Network Layer
Protocol Operations
X Y
C
C
A
A
B
B
Host X Host Y
Application Application
Presentation Presentation
Session Router A Router B Router C Session
Transport Transport
Network Network Network Network Network
Data Link Data Link Data Link Data Link Data Link
Physical Physical Physical Physical Physical
 Each router provides its services to
support upper layer functions

32. Routed Versus Routing Protocol
• Routed protocol
used between
routers to direct
user traffic
Examples: IP, IPX,
AppleTalk, DECnet Network Destination Exit Port
Protocol Network to Use
Protocol Name 1.0 1.1
2.0 2.1
3.0 3.1

33. Routed Versus Routing Protocol
• Routed protocol
used between
routers to direct
user traffic
Examples: IP, IPX,
AppleTalk, DECnet
• Routing protocol
used only between
routers to maintain
routing tables
Examples: RIP, IGRP, OSPF

34. Static Versus Dynamic Routes
Static Route
Uses a protocol route that a network
administrator enters into the router
Dynamic Route
Uses a route that a network protocol
adjusts automatically for topology or
traffic changes

35. Static Route Example
Point-to-point or
A
A circuit-switched
connection
Only a single network
connection with no need B
B
for routing updates
―Stub‖ network
 Fixed route to address reflects
administrator’s knowledge

36. Adapting to Topology Change
A
A B
B
D
D C
C
 Can an alternate route substitute
for a failed route?

37. Adapting to Topology Change
A
A B
B
X
D
D C
C

38. Adapting to Topology Change
A
A B
B
X
D
D C
C
 Can an alternate route substitute
for a failed route?
Yes—With dynamic routing enabled

39. Layers 4–7:
Transport, Session, Presentation,
and Application Layers
© 1999, Cisco Systems, Inc. www.cisco.com

40. Transport Layer
 Segments upper-layer applications
 Establishes an end-to-end connection
 Sends segments from one end host to another
 Optionally, ensures data reliability

41. Transport Layer—
Segments Upper-Layer Applications
Application Electronic File Terminal
Presentation Mail Transfer Session
Session
Transport Application Application
Data Data
Port Port
Segments

42. Transport Layer—
Establishes Connection
Sender Receiver
Synchronize
Negotiate Connection
Synchronize
Acknowledge
Connection Established
Data Transfer
(Send Segments)

43. Transport Layer—
Sends Segments with Flow Control
Transmit
Sender Receiver
Buffer Full
Not Ready
Stop
Process
Segments
Go Ready
Buffer OK
Resume Transmission

44. Transport Layer—
Reliability with Windowing
• Window Size = 1
Send 1 Receive 1
Ack 2
Sender Send 2 Receive 2 Receiver
Ack 3
• Window Size = 3
Send 1 Receive 1
Send 2 Receive 2
Sender
Send 3 Receive 3 Receiver
Ack 4
Send 4

45. Transport Layer—
An Acknowledgement Technique
Sender Receiver
1 2 3 4 5 6 7 1 2 3 4 5 6 7
Send 1
Send 2
Send 3
Ack 4
Send 4
Send 5
Send 6
Ack 5
Send 5
Ack 7

46. Transport to Network Layer
End-to-End Segments
Routed Packets

47. Session Layer
• Network File System (NFS)
• Structured Query Language (SQL)
• Remote-Procedure Call (RPC)
• X Window System
• AppleTalk Session Protocol (ASP)
• DEC Session Control Protocol (SCP)
Service Request
Service Reply
 Coordinates applications as
they interact on different hosts

48. Presentation Layer
• Text • Graphics
• Data • Visual images
ASCII PICT
login:
EBCDIC TIFF
Encrypted JPEG
• Sound GIF
MIDI
• Video
MPEG
QuickTime
 Provides code formatting and
conversion for applications

49. Application Layer
COMPUTER
APPLICATIONS
NETWORK
Word Processor APPLICATIONS INTERNETWORK
Presentation Graphics Electronic Mail
APPLICATIONS
Spreadsheet File Transfer Electronic Data Interchange
Database Remote Access World Wide Web
Design/Manufacturing Client-Server Process E-Mail Gateways
Project Planning Information Location Special-Interest Bulletin Boards
Others Network Management Financial Transaction Services
Others Internet Navigation Utilities
Conferencing (Voice,Video, Data)
Others
 Internetwork applications
can extend beyond the
enterprise (i.e., to suppliers, etc.)

50. Summary
 OSI reference model describes building blocks
of functions for program-to-program
communications between similar or dissimilar
hosts
 Layers 4–7 (host layers) provide accurate data
delivery between computers
 Layers 1–3 (media layers) control physical
delivery of data over the network