Transcript Chap12-Layers

Telecommunications
Concepts
Chapter 1.2
Communications
Systems Modeling
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Contents
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•
•
•
Introduction
Example: a diplomatic negotiation
Principles of a layered model
Communication networks according to a
layered model
• Side-tracks:
–Connection oriented vs. Connectionless
networks.
–The seven layers of the OSI model
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09-07-K.Steenhaut & J.Tiberghien - VUB
Contents
•
•
•
•
Introduction
Example: a diplomatic negotiation
Principles of a layered model
Communication networks according to a
layered model
• Side-tracks:
–Connection oriented vs. Connectionless
networks.
–The seven layers of the OSI model
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09-07-K.Steenhaut & J.Tiberghien - VUB
Layered Network Models
• The problem:
Complexity of networked systems
• The solution:
Decomposition into independent subsystems
• Layered network model
– Introduced by IBM (SNA, 1971)
– Standardized by ITU (X200) and ISO (7498)
– Method universally adopted
– Standards not really obeyed in practice
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09-07-K.Steenhaut & J.Tiberghien - VUB
Contents
•
•
•
•
Introduction
Example: a diplomatic negotiation
Principles of a layered model
Communication networks according to a
layered model
• Side-tracks:
–Connection oriented vs. Connectionless
networks.
–The seven layers of the OSI model
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A diplomatic negotiation
Political arguments
Service Access Points
Translation
Cryptography
Transmission
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A diplomatic negotiation
Political arguments
Service Access Points
Single language messages
Cryptography
Transmission
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09-07-K.Steenhaut & J.Tiberghien - VUB
A diplomatic negotiation
Political arguments
Service Access Points
Single language messages
Encrypted messages
Transmission
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A diplomatic negotiation
Political arguments
Service Access Points
Single language messages
Encrypted messages
Electromagnetic waves
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09-07-K.Steenhaut & J.Tiberghien - VUB
Contents
•
•
•
•
Introduction
Example: a diplomatic negotiation
Principles of a layered model
Communication networks according to a
layered model
• Side-tracks:
–Connection oriented vs. Connectionless
networks.
–The seven layers of the OSI model
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09-07-K.Steenhaut & J.Tiberghien - VUB
Layered Model Definitions
Level (n+1)
entity
Virtual level n+1 communication path
using a level n+1 protocol
Level (n+1)
entity
Physical Communication Path
Level n
Service Access Points
Level (n)
entity
Virtual level n communication path
using a level n protocol
Level (n)
entity
Level n Addresses
Level (n-1) Service Provider
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Layered Model Definitions
Example: The Telephone Service
Virtual Interpersonal communication path
Physical Communication Path
Telephone
Service Access Points
Telephone Numbers
Telephone Network
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Layered Model Definitions
Protocol Data Units
Level (n+1)
entity
(n+1)PDU
Level (n+1)
entity
Level (n)
entity
(n)PDU
Level (n)
entity
Level (n-1) Service Provider
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Layered Model Definitions
Layer overhead
Level (n+1)
entity
Level (n+1)
entity
Connection oriented protocol
Level (n)
entity
Level (n)
entity
Level (n-1) Service Provider
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09-07-K.Steenhaut & J.Tiberghien - VUB
Contents
•
•
•
•
Introduction
Example: a diplomatic negotiation
Principles of a layered model
Communication networks according to a
layered model
• Side-tracks:
–Connection oriented vs. Connectionless
networks.
–The seven layers of the OSI model
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09-07-K.Steenhaut & J.Tiberghien - VUB
Connection oriented communication
Typical example:
A telephone conversation
3 step process:
1. Establish connection
using the signaling protocol
2. Use connection
using an informal protocol
being billed for duration of usage
3. Terminate connection
using the signaling protocol
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Connection oriented communication
A temporary communication channel
is build through the telephone network
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Connection oriented communication
Main points
• Network has a state : the list of active connections
• Network can guarantee Quality Of Service
– Reservation of transmission capacity at connection
establishment
– Monitoring of data transfer and correction of transmission
errors by retransmission
• Network is fragile : state can be lost.
• Application domain :
–
–
–
–
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Very efficient for transferring high volumes of data
Mandatory if stringent Quality Of Service requirements
Poor initial response times due to connection setup
Inapplicable if nodes have high failure rate.
09-07-K.Steenhaut & J.Tiberghien - VUB
Connectionless communication
Typical example:
The postal service
Letters, with an address and a stamp,
are individually carried from a
Post office box to a personal mailbox
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Connectionless communication
No connections are needed to carry mail
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Connectionless communication
Main points
• The network is stateless.
• No guaranteed Quality Of Service.
– No reservation of transmission capacity
– No error correction by retransmission
• Network is robust :
– No state stored in any node
– Each node operates almost independently from others
• Application domain :
– Whenever single message response times are critical
– Whenever nodes are unreliable
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09-07-K.Steenhaut & J.Tiberghien - VUB
Contents
•
•
•
•
Introduction
Example: a diplomatic negotiation
Principles of a layered model
Communication networks according to a
layered model
• Side-tracks:
–Connection oriented vs. Connectionless
networks.
–The seven layers of the OSI model
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A two layers model.
Networks Layer
# Interfaces = # Applications * # Networks
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Interoperability
Connectivity
Applications Layer
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A three layers model.
Networks Layer
# Interfaces = # Applications + # Networks
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Connectivity
Internet & Transport Layer
Interoperability
Applications Layer
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The Internet & Transport Layer
Applications Layer
Transport Layer
Internet Layer
Networks Layer
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The Internet & Transport Layers
Example: www
http
TCP
IP
IP
SKYNET
UUNET
Networks Layer
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Contents
•
•
•
•
Introduction
Example: a diplomatic negotiation
Principles of a layered model
Communication networks according to a
layered model
• Side-tracks:
–Connection oriented vs. Connectionless
networks.
–The seven layers of the OSI model
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The 7 OSI layers
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Interoperability
Connectivity
Applications Layers
Internet & Transport Layer
7 : Application
6 : Presentation
5 : Session
4 : Transport
3 : Network
Networks Layers
2 : Data Link
1 : Physical
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Introduced concepts
• Layered communications system
– protocol = horizontal convention
– Service access point & address
• Connectivity :
– service offered by lower layers
• Interoperability :
– full communications services
• Connection Oriented Communications
• Connectionless Communications
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Bibliography
To know More about network modeling
Fred Halsall
Data Communications,
Computer Networks
and Open Systems
Fourth Edition
Addison-Wesley 1995.
ISBN 0-201-42293-X
Recommended for this chapter
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