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THE OSI MODEL
ISO is the organization.OSI is the model.
ISOInternational Standards Organization
OSIOpen Systems Interconnection
THE MODEL
ApplicationApplication
PresentationPresentation
SessionSession
TransportTransport
NetworkNetwork
DatalinkDatalink
PhysicalPhysical
7
6
54
3
2
1
Layered Architecture
Application7-6 Interface
Presentation6-5 Interface
Session5-4 Interface
Transport4-3 Interface
Network3-2 Interface
Datalink2-1 Interface
Physical
Application7-6 Interface
Presentation6-5 Interface
Session5-4 Interface
Transport4-3 Interface
Network3-2 Interface
Datalink2-1 Interface
Physical
Network
Datalink
Physical
Network
Datalink
Physical
3rd
2nd
1st
3rd
2nd
1st
3rd
2nd
1st
Peer-to-peer protocol (7 th layer)
Peer-to-peer protocol (6 th layer)
Peer-to-peer protocol (5 th layer)
Peer-to-peer protocol (4 th layer)
Physical communication
Device A Device BIntermediatenode
Intermediatenode
7
6
5
4
3
2
1
7
6
5
4
3
2
1
Peer-to-peer Processes
Interface between Layers
Organization of the Layers
Layer 1 , 2 and 3 physical, data link and network Are network support layer;
เป็�นการส่งข้�อมู�ลทางกายภาพ จากอ�ป็กรณ์�ตั�วหน��งไป็ย�งหลาย ๆ อ�ป็กรณ์� (electrical Specifications,physical connection, physical addressing,transport timeing)
Layer 5 , 6 and 7 session , presentation and application
The user support layer; interoperability among unrelated software system
Layer 4 transport layer เป็�นส่วนเชื่#�อมูตัอระหวาง layer ท%�อย� บนและลาง (hardware ,software)
An exchange using the OSI model
L7 dataL7 dataH6
L6 data H5L5 data H4
L4 data H3L3 data H2T2
010101010101101010000010000
7654321
7654321
Transmission medium
L7 dataL7 dataH6
L6 data H5L5 data H4
L4 data H3L3 data H2T2
010101010101101010000010000
Function of the layers
Physical layer
L2 data
10101000000010
From data link layer
Physical layer
Transmission medium
L2 data
10101000000010
To data link layer
Physical layer
ส่(�งท%�จะพ(จารณ์าในข้�*นตัอนการท+างานข้อง physical layer
• Line configuration
• Data transmission mode
• Topology
• Signal
• Encoding
• Interface
• Medium
Data Link layer
L3 data
From Network layer
DataLink layer
H2T2 Frame
10101000000010
To Physical layer
L3 data
To Network layer
DataLink layer
H2T2 Frame
10101000000010
From Physical layer
Specific responsibilities of the data link layer include the following;
Node to node delivery
Addressing
Access control
Flow control
Error handling
Synchronization
LLCLogical Link ControlMACMedia Access Control
Example Data link layer
DataT2 10 87
Trailer Sourceaddress
Destinationaddress
10 28 53 65 87
Network layer
L4 data
From transport layer
To data link layer
H3 Packet
L3 data
Networklayer
L4 data
To transport layer
From data link layer
H3 Packet
L3 data
Networklayer
Specific responsibilities of the network layer include the following;
Source-to-destination delivery
Logical addressing
Routing
Address transformation
Multiplexing
10
Example Network layer
87
DataT2 10 20A PR
45
71
95 77
DataT2 66 95A P
DataT2 99 33A PRing
R33
66
99
20F
T
N
Z
Bus
Bus
G
EA
P
Transport layer
L5 data
From session layer
To network layer
H4
L4 data
Transportlayer H4 H4
L4 data
L4 data
L5 data
To session layer
From network layer
H4
L4 data
TransportlayerH4 H4
L4 data
L4 data
Specific responsibilities of the transport layer include the following;
End-to-end massage delivery
Service-point (port) addressing
Segmentation and reassemble
Connection control
Example Transport layer
Data j k
A
Data2 j k A P
Data1 j k A P
Data2 j k A P H2T2
Data1 j k A P H2T2
Data j k
B
Data2 j k A P
Data1 j k A P
Data2 j k A P H2T2
Data1 j k A P H2T2
Physical linkPhysical link
Transport layer
Networklayer
Data linklayer
Session layer
L6 data
From presentation layer
To transport layer
L5 data
H5
Sessionlayer
syn syn syn
L6 data
To presentation layer
From transport layer
L5 data
H5
Sessionlayer
syn syn syn
Specific responsibilities of the session layer include the following;
Session management
Synchronization
Dialog control
Graceful close
Presentation layer
L7 data
From application layer
To session layer
L6 data
Presen-tationlayer
Encode,encrypted,andCompresses data
H6
L7 data
To application layer
From session layer
L6 data
Presen-tationlayer
Encode,encrypted,andCompresses data
H6
Specific responsibilities of the presentation layer include the following;
Translation
Encryption
Compression
Security
Application layer
To presentation layer
L7 data
Applicationlayer
X.500 FTAM X.400
User
From presentation layer
L7 data
Applicationlayer
X.500 FTAM X.400
User
Specific responsibilities of the application layer include the following;
Network virtual terminal
File access transfer,and management
Mail services
Directory services
Summary of Layer Function
Application
Presentation
Session
Transport
Network
Data Link
Physical
To allow access to network resources
To translate,encrypt, and compress data
To establish,manage,and terminate sessionTo provide reliable end to end message Delivery and error recoveryTo move packets from source to Destination; to provide internetworkingTo organize bit into frames; to provideNode to node deliveryTo transmit bits over a medium; toProvide mechanical and electrical specification
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