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

2. Why Network Protocol Models?
ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model
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

3. Who define Network Model?
ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model
Who define Network Model?
Need non-profit making organizations
ISO - International Standards Organization
e.g. OSI, MPEG-1, 2, 4, etc. (
IEEE - Institute of Electrical & Electronic Engineers
e.g IEEE 802, IEEE 754, etc. (
ITU - International Telecommunication Union
e.g. V.34, H.323, H.324, etc. (

4. The OSI 7-layer Model OSI - Open Systems Interconnection
ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model
The OSI 7-layer Model
OSI - Open Systems Interconnection
Defined in 1984 and become an international standard
All
Away
People
Pizza
Seem
Sausage To
Throw
Need
Not
Data Do
Processing
Please

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

6. Relationship of OSI layers
ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model
Relationship of OSI layers
Virtual
Communication
Physical
Communication

7. Protocols in a layered architecture
ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model
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

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

9. ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model
1. Physical Layer
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
Pres.
Pres.
Sess.
Sess.
Tran.
Tran.
Netw.
Netw.
Data.
Data.
Phys.
Phys.

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

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

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

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

14. 4. Transport Layer Example protocols: TCP, SPX, NWLink
ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model
4. Transport Layer
Example protocols: TCP, SPX, NWLink
Ensure packets are delivered error free, in sequence
Translate between packets and message
Appl.
Appl.
Pres.
Pres.
Sess.
Sess.
Tran.
Tran. 1 2 3
Sending 1 3 2
Receiving
Netw.
Netw.
Data.
Data.
Phys.
Phys.

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

16. ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model
What is a Session?
A. Consecutive sessions on a transport layer connection
B. Consecutive sessions on a multiple transport layer connections 1 2 3 1 2 3
C. Both 1 2 3

17. ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model
6. Presentation Layer
Example application program: redirector (NT), SSL
Appl.
Appl.
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
Pres.
Pres.
Sess.
Sess.
Tran.
Tran.
Netw.
Netw.
Data.
Data.
Phys.
Phys.

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

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

20. Utility: WS_FTP ENG224 INFORMATION TECHNOLOGY – Part I
6. Network Model
Utility: WS_FTP

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

22. The 802 Project Model IEEE launched the Project 802 in 1980 February
ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model
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

23. ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model
IEEE 802 Categories
802.1 Internetworking Logical Link Control (LLC)
802.3 Carrier-Sense Multiple Access with Collision Detection (CSMA/CD) LAN (Ethernet)
802.4 Token Bus LAN 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
Network Security Wireless Networks
Demand Priority Access LAN, 100 BaseVG-AnyLAN

24. Enhancements to the OSI Model
ENG224
INFORMATION TECHNOLOGY – Part I
6. Network Model
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

25. Logical Link Control (LLC)
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