ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model
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6. Network Model

ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model
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• Network communication is an extremely complex task
• Need cooperative efforts from all nodes involved
•
A standard model helps to describe the task of a networking product or service
•
Also help in troubleshooting by providing a frame of reference

ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model
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• Need non-profit making organizations
•
ISO - International Standards Organization e.g. OSI , MPEG-1, 2, 4, etc. (http://www.iso.ch/)
•
IEEE - Institute of Electrical & Electronic
Engineers e.g IEEE 802, IEEE 754, etc. (http://www.ieee.org)
• ITU - International Telecommunication Union e.g. V.34, H.323, H.324, etc. (http://www.itu.int)

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ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model
• OSI - Open Systems Interconnection
•
Defined in 1984 and become an international standard
A ll
P eople
S eem
T o
N eed
D ata
P rocessing
A way
P izza
S ausage
T hrow
N ot
D o
P lease

ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model
•
Layering specifies different level of functions and services
•
Each layer works with the layer below and above it
•
Each layer provides services to next layer
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•
Shield the upper layer from the details of actual implementation

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ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model
Virtual
Communication
Physical
Communication

ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model
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•
Network communication is possible only if machines speaking the same languages ( protocols )
•
Since each layer work independently, each layer speaks different languages ( protocols )
•
Lead to the concept of a Protocol Stack
• Network communication is possible only if the
Protocol Stacks on two machines are the same

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ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model
• To identify the language (protocol) of each layer, identifier (header and trailer) are added to data

ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model
Example protocols: Ethernet, Token Ring (Physical part)
Appl.
Appl.
• Define how cable is attached to the Network Adapter Card
•
How many pins in the connector?
•
The impedance?
•
Max/min electrical voltage?
•
Responsible for transmitting bits from one computer to another
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Pres.
Sess.
Tran.
Netw.
Data.
Phys.
Pres.
Sess.
Tran.
Netw.
Data.
Phys.

ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model
Example protocols: Ethernet, Token Ring
Appl.
•
Make data frames
Pres.
Frame
• Provide error-free frame transfer by acknowledgment
10 and retransmission
Sess.
Tran.
Netw.
Data.
Phys.
Appl.
Pres.
Sess.
Tran.
Netw.
Data.
Phys.

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ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model

ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model
Example protocols: IP, IPX
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Logical address to physical address translation
For TCP/IP running on Ethernet
Logical address: IP address
158.132.148.99
Physical address: Ethernet address
00 00 E2 15 1A CA
•
Determine the route from
12 source to destination computer
Appl.
Pres.
Sess.
Tran.
Netw.
Data.
Phys.
Appl.
Pres.
Sess.
Tran.
Netw.
Data.
Phys.

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ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model

ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model
Example protocols: TCP, SPX, NWLink
• Ensure packets are delivered error free , in sequence
Appl.
Pres.
• Translate between packets and message
Sess.
Tran.
Netw.
Data.
Phys.
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Appl.
Pres.
Sess.
Tran.
Netw.
Data.
Phys.

ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model
Example application program: Winsock, UNIX Socket
• Establishment, maintaining and release of session
• Provide dialog management
Appl.
Pres.
Sess.
•
Regulate which side transmit, when, for how long (Sync.)
Tran.
Netw.
•
Provide synchronization between user tasks
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Data.
Phys.
Appl.
Pres.
Sess.
Tran.
Netw.
Data.
Phys.

ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model
A. Consecutive sessions on a transport layer connection
1 2 3
B. Consecutive sessions on a multiple transport layer connections
1 2 3
1
C. Both
2 3
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ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model
Example application program: redirector (NT), SSL
•
Translate data from
Application Layer to the format suitable for session layer (the network)
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Provide data encryption , compression
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Changing or converting character set, graphic, and file
17 format
Appl.
Pres.
Sess.
Tran.
Netw.
Data.
Phys.
Appl.
Pres.
Sess.
Tran.
Netw.
Data.
Phys.

ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model
Example protocols: FTP, Telnet, HTTP
•
Entry point for application to access network
Appl.
Pres.
•
Directly support user applications
Sess.
Tran.
•
E.g. File transfer, email
Netw.
• General capabilities:
Data.
Network access, flow control,
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Error recovery Phys.
Appl.
Pres.
Sess.
Tran.
Netw.
Data.
Phys.

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ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model
• The most traditional network task
•
Implemented by a simple Application Layer protocol called FTP
FTP Client FTP Server
PictureTel
Network

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ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model

ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model
WS_FTP
PictureTel
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FTP Client
Layers 5-7
Layer 4
Layer 3
FTP
TCP
IP
Layers 1,2 Ethernet
FTP
TCP
IP
FTP Server
Layers 5-7
Layer 4
Layer 3
Ethernet
Layers 1,2

ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model
• IEEE launched the Project 802 in 1980 February
•
Predate the ISO standard, but the development was performed in roughly the same time
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Objective : To clearly define the network standards for different kind of physical components of a network - the interface card and the cabling
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• Enhance the Data Link and Physical layers of the
OSI model

ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model
802.1
Internetworking 802.2
Logical Link Control (LLC)
802.3
Carrier-Sense Multiple Access with Collision
Detection (CSMA/CD) LAN (Ethernet)
802.4
Token Bus LAN 802.5
Token Ring LAN
802.6
Metropolitan Area Network (MAN)
802.7
Broadband Technical Advisory Group
802.8
Fiber-Optic Technical Advisory Group
802.9
Integrated Voice/Data Networks
802.10
Network Security 802.11
Wireless Networks
802.12
Demand Priority Access LAN, 100 BaseVG-AnyLAN
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ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model
• Divide the Data Link layer into 2 sub-layers
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Logical Link Control Sub-layer
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•
Define the use of service access points (SAPs) as an interface for higher layer to Data Link layer
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Media Access Control Sub-layer
•
Directly interface with the network card
•
For delivering error-free data communications

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ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model
Logical Link
Control
(LLC)
802.1
802.2
Media Access
Control (MAC)
802.3
802.4
802.5
802.12