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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


L a y e r

P r e s e n t a t io n

L a y e r


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


H O S T

N O D E

H O S T

N O D E


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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


L a y e r


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


D a t a

H e a d e r o f


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 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


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


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


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



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


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

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