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Protocol ArchitectureThe Common Language
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Copyright by Jorg Liebeherr 98, 99
Need for Protocols
Protocols are a set of rulesand conventions. By enforcingthat communicating parties adhere
to a common protocol,communication is made possible.
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Network Architecture
ANetwork Architecture is astructured set of protocols thatimplement the exchange of
information between computers
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Programming the
Communication Any complex programming task is made
simpler by using several levels of abstraction
Abstraction hides the programming details oflower levels Communication tasks give rise to standard
abstractions
Committees such as the IETF (InternetEngineering Task Force) are in charge forstandardizing the abstractions related tointernet communication
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The Levels of Abstraction Multiple levels of communication abstractions
have been defined by standardization bodies
Each level is enforced by a correspondingprotocol Each level uses the abstract services of the
level below
Abstraction achieves separation of concerns A protocol neednt know how the lower-level
abstractions are implemented and what the higherlevel abstractions are.
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Layered Network Architecture In a Layered Network Architecture, the
services are grouped in a hierarchy of layers.
A protocol oflayer N uses only services oflayer N-1. A protocol oflayer N provides services only to layer
N+1.
A
C
E
B
D E
B l a y e r 3
l a y e r 2
l a y e r 1
n o t l a y e r e d l a y e r e d
A
C
D
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Service Primitives
N+1 LayerEntity
N+1 LayerEntity
N LayerEntity
N LayerEntity
N+1 Layer Protocol
X. Request X. Indication X. ResponseX. Confirm
Assume that some protocol implementsservice X.
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Service PrimitivesRecall: A layer N+1 protocol entity sees thelower layers only as an abstract service
providerN+1 Layer
EntityN+1 Layer
Entity
N+1 Layer Protocol
X. Request X. IndicationX. Confirm
Service Provider
X. Response
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Example: Sending a Letter
Bobsmailbox
Bob Alice
Alicesmailbox
Postman
Logical flow of information
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(Un-)Acknowledged Service Unconfirmed service:
Acknowledged service:
US MailL.Request L.Indicate
L.IndicateL.Confirm
US Mail
L.Request L.Indicate
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Protocol Architectures There are only few protocol
architectures that are relevanttoday: OSI Reference Model
TCP/IP Protocols SuiteATM Protocol Stack
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OSI Reference Model The OSI model defines seven layers:
Layer 7: Application Layer
Layer 6: Presentation LayerLayer 5: Session Layer
Layer 4: Transport Layer
Layer 3: Network LayerLayer 2: Data Link Layer
Layer 1: Physical Layer
Interconnection Media
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OSI Layers
P h y s ic a l
L a y e r
P h y s ic a l
L a y e r
P h y s ic a l
L a y e r
P h y s ic a l
L a y e r
D a t a L in k
L a y e r
D a t a L in k
L a y e r
D a t a L in k
L a y e r
D a t a L in k
L a y e r
N e t w o r k
L a y e r
S e s s io n
L a y e r
S e s s io n
L a y e r
T r a n s p o r t
L a y e r
T r a n s p o r t
L a y e r
A p p l i c a t io n
L a y e r
A p p l i c a t io n
L a y e r
P r e s e n t a t io n
L a y e r
P r e s e n t a t io n
L a y e r
N e t w o r k
L a y e r
N e t w o r k
L a y e r
N e t w o r k
L a y e r
A p p l i c a t io n
H O S T
N O D E
H O S T
N O D E
A p p l i c a t io n
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OSI Layers and Encapsulation
P h y s i c a l
L a y e r
P h y s i c a l
L a y e r
D a t a L i n k
L a y e r
D a t a L i n k
L a y e r
N e t w o r k
L a y e r
S e s s i o n
L a y e r
S e s s i o n
L a y e r
T r a n s p o r t
L a y e r
T r a n s p o r t
L a y e r
A p p l ic a t io n
L a y e r
A p p l i c a t i o n
L a y e r
P r e s e n t a t io n
L a y e r
P r e s e n t a t io n
L a y e r
N e t w o r k
L a y e r
A p p l i c a t i o n A p p l i c a t i o n
A H
P H
S H
T H
N H
D H
B i t s
D a t a
A H D a t a
P H A H D a t a
S H P H A H D a t a
T H S H P H A H D a t a
N H T H S H P H A H D a t a
D a t a
A p p l i c a t i o n
D a t a
H e a d e r o f
A p p l i c a t i o n
L a y e r
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OSI Model in a Switched
Communication Network
T r a n s p o r t
S e s s i o n
P r e s e n t a t i o n
A p p l i c a t i o nT r a n s p o r t
S e s s i o n
P r e s e n t a t i o n
A p p l i c a t i o n
P h y s i c a l
D a t a L i n k
N e t w o r k
P h y s i c a l
D a t a L i n k
N e t w o r k
P h y s i c a l
D a t a L i n k
N e t w o r k
P h y s i c a l
D a t a L i n kN e t w o r k
P h y s i c a l
D a t a L i n k
N e t w o r k
P h y s i c a lD a t a L i n k
N e t w o r k
S t a t i o n ( H o s t )
N o d e ( R o u t e r )
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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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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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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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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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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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A Tour of the OSI Layers Presentation Layer (Layer 6):
Data conversion into application format Encryption/decryption Secure sockets
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A Tour of the OSI Layers Application Layer (Layer 7):
Provides network access to applicationprograms
Everything is application specific Example: File Transfer, Electronic Mail
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TCP/IP Protocol Suite The TCP/IP protocol suite
was first defined in 1974
The TCP/IP protocol suiteis the protocolarchitecture of theInternet
The TCP/IP suite has fourlayers:Application, Transport,Internet, and Network
Interface Layer
A p p l i c a t i o n
L a y e r
T r a n s p o r t
L a y e r
I n t e r n e t
N e t w o r k
I n t e r f a c e
t e l n e t , f t p , e m a i l
T C P , U D P
I P , I C M P , I G M P
D e v i c e D r i v e r s
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Example: File Transfer
F T P
p r o g r a m
T C P
I P
E t h e r n e t
D r i v e r
E t h e r n e t
D r i v e r
E t h e r n e t
D r i v e r
I P
F T P
p r o g r a m
T C P
I P
E t h e r n e t
D r i v e r
F T P p r o t o c o l
T C P p r o t o c o l
I P p r o t o c o l I P p r o t o c o l
E t h e r n e t
p r o t o c o l
E t h e r n e t
p r o t o c o l
Host A Router Host B
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Encapsulation in the TCP/IP
Suite
A p p l i c a t i o n
T C P
I P
E t h e r n e t
D r i v e r
U s e r d a t a
U s e r d a t aA p p l i c a t i o nH e a d e r
A p p l i c a t i o n d a t aT C P H e a d e r
A p p l i c a t i o n d a t aT C P H e a d e r I P H e a d e r
A p p l i c a t i o n d a t aT C P H e a d e r I P H e a d e r E t h e r n e t
H e a d e r
E t h e r n e t
T r a i l e r
I P d a t a g r a m
T C P s e g m e n t
E t h e r n e t f r a m e
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TCP/IP Protocol Suite
A p p l i c a t i o n
L a y e r
N e t w o r k
L a y e r
L i n k L a y e r
I P
A R PH a r d w a r e
I n t e r f a c eR A R P
M e d i a
I C M P I G M P
T r a n s p o r t
L a y e r T C P U D P
U s e r
P r o c e s s
U s e r
P r o c e s s
U s e r
P r o c e s s
U s e r
P r o c e s s
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Comparison of OSI Model and
TCP/IP Suite
A p p l i c a t i o n
P r e s e n t a t i o n
S e s s i o n
T r a n s p o r t
N e t w o r k
D a t a L i n k
P h y s i c a l
A p p l i c a t i o n
T r a n s p o r t
I n t e r n e t w o r k
N e t w o r k
A c c e s s
P h y s i c a l
O S I T C P / I P
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Quiz Name one function of the network layer