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1. Top school in Ghaziabad
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2. Protocol Architecture
The “Common Language”
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3. Need for Protocols
 Protocols are a set of rules and
conventions. By enforcing that
communicating parties adhere to a
common protocol, communication
is made possible.
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Copyright by Jorg Liebeherr 98, 99

4. Network Architecture
 A Network Architecture is a
structured set of protocols that
implement the exchange of
information between computers
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5. Programming the
Communication
 Any complex programming task is made
simpler by using several levels of abstraction
 Abstraction hides the programming details of
lower levels
 Communication tasks give rise to standard
abstractions
 Committees such as the IETF (Internet
Engineering Task Force) are in charge for
standardizing the abstractions related to
internet communication
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Copyright by Jorg Liebeherr 98, 99

6. The Levels of Abstraction
 Multiple levels of communication abstractions
have been defined by standardization bodies
 Each level is enforced by a corresponding
protocol
 Each level uses the abstract services of the
level below
 Abstraction achieves separation of concerns
 A protocol needn’t know how the lower-level
abstractions are implemented and what the higher
level abstractions are.
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7. Layered Network Architecture
 In a Layered Network Architecture, the
services are grouped in a hierarchy of layers.
 A protocol of layer N uses only services of layer N-1.
 A protocol of layer N provides services only to layer
N+1.
A
Copyright by Jorg Liebeherr 98, 99
C
E
B
D E
B layer 3
layer 2
layer 1
not layered layered
A
C
D
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8. Service Primitives
 Assume that some protocol implements
service “X”.
N+1 Layer
Entity
Copyright by Jorg Liebeherr 98, 99
N+1 Layer
Entity
N Layer
Entity
N Layer
Entity
N+1 Layer Protocol
X. Request X. Confirm X. Indication X. Response
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9. Service Primitives
Recall: A layer N+1 protocol entity sees the
lower layers only as an abstract service
provider
N+1 Layer
Entity
Copyright by Jorg Liebeherr 98, 99
N+1 Layer
Entity
N+1 Layer Protocol
X. Request X. Confirm X. Indication
Service Provider
X. Response
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10. Example: Sending a Letter
Logical flow of information
Bob Alice
Bob’s
mailbox
Copyright by Jorg Liebeherr 98, 99
Alice’s
mailbox
Postman
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11. (Un-)Acknowledged Service
 Unconfirmed service:
 Acknowledged service:
L.Request L.Indicate
Copyright by Jorg Liebeherr 98, 99
US Mail
L.Request L.Indicate
US Mail
L.Confirm L.Indicate
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12. Protocol Architectures
 There are only few protocol
architectures that are relevant
today:
 OSI Reference Model
 TCP/IP Protocols Suite
 ATM Protocol Stack
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13. OSI Reference Model
 The OSI model defines seven layers:
Copyright by Jorg Liebeherr 98, 99
Layer 7: Application Layer
Layer 6: Presentation Layer
Layer 5: Session Layer
Layer 4: Transport Layer
Layer 3: Network Layer
Layer 2: Data Link Layer
Layer 1: Physical Layer
Interconnection Media
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14. OSI Layers
HOST
Session
Lay er
Phy sical
Lay er
Copyright by Jorg Liebeherr 98, 99
Phy sical
Lay er
Phy sical
Lay er
Phy sical
Lay er
Data Link
Lay er
Data Link
Lay er
Data Link
Lay er
Data Link
Lay er
Network
Lay er
Session
Lay er
Transport
Lay er
Transport
Lay er
Application
Lay er
Application
Lay er
Presentation
Lay er
Presentation
Lay er
Network
Lay er
Network
Lay er
Network
Lay er
Application
NODE
HOST
NODE
Application
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15. OSI Layers and Encapsulation
Data
Application
Data
Application Application
Session
Lay er
Phy sical
Lay er
Copyright by Jorg Liebeherr 98, 99
Phy sical
Lay er
Data Link
Lay er
Data Link
Lay er
Network
Lay er
Session
Lay er
Transport
Lay er
Transport
Lay er
Application
Lay er
Application
Lay er
Presentation
Lay er
Presentation
Lay er
Network
Lay er
AH
PH
SH
Header of
Application
Layer
TH
NH
DH
Bits
Data
AH Data
PH AH Data
SH PH AH Data
TH SH PH AH Data
NH TH SH PH AH Data
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16. OSI Model in a Switched
Communication Network
Node (Router)
Application
Presentation
Session
Transport
Network
Data Link
Copyright by Jorg Liebeherr 98, 99
Application
Presentation
Session
Transport
Network
Data Link
Physical
Network
Data Link
Physical
Network
Data Link
Physical
Network
Data Link
Physical
Network
Data Link
Physical
Physical
Station (Host)
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17. A Tour of the OSI Layers
 Physical Layer (Layer 1):
 Converts bits into electrical or optical
signals
 Transmits these signals over the hardware
communication medium
 Example: RS-232
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Copyright by Jorg Liebeherr 98, 99

18. A Tour of the OSI Layers
 Data Link Layer (Layer 2):
 Reliably transfers frames over a link
 Performs synchronization, error control,
flow control
 Example: PPP
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Copyright by Jorg Liebeherr 98, 99

19. A Tour of the OSI Layers
 Network Layer (Layer 3):
 Moves packets inside the network
 Performs routing, addressing, switching,
congestion control
 Example: IP
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20. A Tour of the OSI Layers
 Transport Layer (Layer 4):
 Controls delivery of data between hosts
 Connection management, error control,
flow control, multiplexing, TCP, UDP.
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Copyright by Jorg Liebeherr 98, 99

21. A Tour of the OSI Layers
 Session Layer (Layer 5):
 Support the dialog between cooperating
application programs
 Session management, synchronization
 Example: RPC
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Copyright by Jorg Liebeherr 98, 99

22. A Tour of the OSI Layers
 Presentation Layer (Layer 6):
 Data conversion into application format
 Encryption/decryption
 Secure sockets
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Copyright by Jorg Liebeherr 98, 99

23. A Tour of the OSI Layers
 Application Layer (Layer 7):
 Provides network access to application
programs
 Everything is application specific
 Example: File Transfer, Electronic Mail
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Copyright by Jorg Liebeherr 98, 99

24. TCP/IP Protocol Suite
 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
Copyright by Jorg Liebeherr 98, 99
Application
Layer
Transport
Layer
Internet
Network
Interface
telnet, ftp, email
TCP, UDP
IP, ICMP, IGMP
Device Drivers
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25. Example: File Transfer
Host A Router Host B
FTP
program
TCP
IP
Ethernet
Driver
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Ethernet
Driver
Ethernet
Driver
IP
FTP
program
TCP
IP
Ethernet
Driver
FTP protocol
TCP protocol
IP protocol IP protocol
Ethernet
protocol
Ethernet
protocol
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26. Encapsulation in the TCP/IP
Suite
Application
TCP
IP
Ethernet
Driver
Copyright by Jorg Liebeherr 98, 99
User data
User data Application
Header
TCP Header Application data
TCP segment
IP Header TCP Header Application data
IP Header TCP Header Application data
Ethernet
Header
Ethernet
Trailer
IP datagram
Ethernet frame
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27. TCP/IP Protocol Suite
User
Process
ICMP IGMP
Copyright by Jorg Liebeherr 98, 99
Application
Layer
Network
Layer
Link Layer
IP
ARP
Hardware
Interface
RARP
Media
Transport
Layer
TCP UDP
User
Process
User
Process
User
Process
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28. Comparison of OSI Model and
TCP/IP Suite
OSI TCP/IP
Application
Presentation
Session
Transport
Network
Data Link
Physical
Copyright by Jorg Liebeherr 98, 99
Application
Transport
Internetwork
Network
Access
Physical
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29. Quiz
 Name one function of the network layer
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