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6. 6. Network ModelNetwork Model
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Why Network Protocol Models?
• 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
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Who define Network Model?
• 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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The OSI 7-layer Model
All
People
Seem
To
Need
Data
Processing
Away
Pizza
Sausage
Throw
Not
Do
Please
• OSI - Open Systems Interconnection
• Defined in 1984 and become an international standard
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Layered Architecture
• 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
• Shield the upper layer from the details of actual implementation
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Relationship of OSI layers
VirtualCommunication
PhysicalCommunication
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Protocols in a layered architecture
• 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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• To identify the language (protocol) of each layer, identifier (header and trailer) are added to data
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1. Physical Layer
• 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
Example protocols: Ethernet, Token Ring (Physical part)
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2. Data Link Layer
• Make data frames
• Provide error-free frame transfer by acknowledgment and retransmission
Example protocols: Ethernet, Token Ring
Frame
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3. Network Layer
• 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 source to destination computer
Example protocols: IP, IPX
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4. Transport Layer
• Ensure packets are delivered error free, in sequence
• Translate between packets and message
1 3 2
Receiving
1 2 3
Sending
Example protocols: TCP, SPX, NWLink
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5. Session Layer Example application program: Winsock, UNIX Socket
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• Establishment, maintaining and release of session
• Provide dialog management
• Regulate which side transmit, when, for how long (Sync.)
• Provide synchronization between user tasks
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A. Consecutive sessions on a transport layer connection
1 2 3
B. Consecutive sessions on a multiple transport layer connections
1 2 3
What is a Session?
C. Both
1 2 3
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6. Presentation Layer Example application program: redirector (NT), SSL
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• Translate data from Application Layer to the format suitable for session layer (the network)
• Provide data encryption, compression
• Changing or converting character set, graphic, and file format
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7. Application Layer Example protocols: FTP, Telnet, HTTP
• Entry point for application to access network
• Directly support user applications
• E.g. File transfer, email
• General capabilities:
Network access, flow control, Error recovery
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Example: File Transfer
PictureTelPictureTel
PictureTel
FTP ServerFTP Client
Network
• The most traditional network task
• Implemented by a simple Application Layer protocol called FTP
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Utility: WS_FTP
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FTP
TCP
IP
Ethernet
FTP
TCP
IP
Ethernet
PictureTelPictureTel
PictureTel
FTP ServerFTP Client
WS_FTP
Layers 1,2
Layer 3
Layer 4
Layers 5-7
Layers 1,2
Layer 3
Layer 4
Layers 5-7
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The 802 Project Model
• IEEE launched the Project 802 in 1980 February
• Predate the ISO standard, but the development was performed in roughly the same time
• Objective: To clearly define the network standards for different kind of physical components of a network - the interface card and the cabling
• Enhance the Data Link and Physical layers of the OSI model
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IEEE 802 Categories 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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Enhancements to the OSI Model
• Divide the Data Link layer into 2 sub-layers
• Logical Link Control Sub-layer
• Define the use of service access points (SAPs) as an interface for higher layer to Data Link layer
• Media Access Control Sub-layer
• Directly interface with the network card
• For delivering error-free data communications
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Media AccessControl (MAC)
Logical Link Control (LLC)
802.3802.3 802.4802.4
802.5802.5 802.12802.12
802.2802.2
802.1802.1
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