1. OSI Layered framework for the design of network systems that allows communication across all types of
computers system.
2. The OSI 7 layers.(Brief functional overview.)
3. Vertical and horizontal communication between the layers using interface.(defines what information and service should the layer provide to the layer above it.)
4. Data Encapsulation
a) PDU conception-each protocol on the diff. layer has it's own format.
b) Headers are added while a packet is going down the stack at each layer.
c) Trailers are usually added on the second layer.
Comparison with TCP/IP
- Pretty similar to OSI.
- TCP/IP has less layers(four)
- Main difference in layers is after layer 4.
Layers
- Application layer(Layer 7)
Application layer interact with application program and is the highest level of OSI model. application layer of OSI model marks the spot where users actually communicate to the computer.
The application layer contains variety of protocols that are commonly needed by user.
One widely used application protocols is HTTP which is basis for www. when browser wants a web page.
Other application protocols are used for file transfer (FTP), E mail ( SMTP).
◦Provides user interfaces and support for services◦Resource sharing and device redirection◦Remote file access◦Remote printer access◦Inter-process communication◦Network management◦Directory services◦Electronic messaging (such as mail)◦Network virtual terminals
- Presentation layer(Layer 6)
A presentation layer present data to the application layer and is responsible for data translation and cord formatting.
A successful data transfer technique is to adapt the data into a standard format before transmission. by providing translation service the presentation layer ensure that data transfer ed format. The application layer of one system can be read by the application layer of another one.
The OSI has protocol standards that define how standard data should be formatted. Task like data compression, decompression, encryption and decryption are associated with this layer.
This is the layer at which application programmers consider data structure and presentation. Example: GIF, JPEG, TIFF, etc.
◦Translation (connects different computer systems)◦Compression (transmission efficiency)
◦Encryption (SSL security)
- Session layer (Layer 5)
Session layer provides mechanism for controlling the dialogue between the tow end system. It define how to start, control and end conversation (call session) between applications.
It coordinate communication between systems, and serves to organize their communication by offering three different modes: simplex, half duplex, and full duplex.
An other service that is offered as a part of the session layer might include data synchronization.
◦Session
establishment, maintenance and termination (Deciding who sends, and when.)
◦Session support (security, name recognition, logging )
- Transport layer (Layer 4)
Transport layer segments and reassemble data into a data stream.Service located in the transport layer both segment and reassemble data from upper-layer applications and unite it onto the some data stream.
They provide end-to-end data transport service and can establish a logical connection between the sending host and destination host on an network.
◦Connectionless and connection-oriented services◦Process-Level Addressing◦Multiplexing and Demultiplexing◦Segmentation, Packaging and Reassembly◦Connection Establishment, Management and Termination◦Acknowledgments and Retransmissions
◦Flow Control
- Network layer(Layer 3)
The network layer manage device addressing, tracks the location of device on the net work, and determines the best way to move data, which means that the network layer must transport traffic between devices that aren't locally attached.
Routers are specified at the network layer and provide the routing service within an inter network.
◦Logical Addressing
◦Routing
(where the packet is destinated to)
◦Datagram
Encapsulation
◦Fragmentation
and Reassembly (handling too big packets )
◦Error
Handling and Diagnostics ( using status messages for example
)
- Data link layer (Layer 2)
Data link layer provides the physical transmission of the data and handles errors notification, network topology, and flow control. This means the data link layer will ensure that massages are delivered to the proper device on a LAN using hardware addresses, and translate massages from network layer into bits for the physical layer to transmit.
The data link layer formats the massage into pieces, each called a data frame, and adds a customized header containing the hardware destination and source address.
2.1. Logical Link Control (LLC )
◦Establishment and control of logical
links between local devices on a network.
2.2. Media Access Control (MAC)
◦The procedures used by devices to control
access to the network medium.
•Frame
sequencing
•Frame
acknowledgment
•Addressing
•Frame
delimiting
•Frame
error checking
•PDU: frame
- Physical layer (Layer 1)
Physical layer specifies the electrical, mechanical, procedural and functional requirement for activating a physical link between end system.
Physical layer does tow thin-
- It sends bits and receives bits. Bits come only in value of 1 and 0. The physical layer communicate with various type of actual communicate media. Different kind of media represent these bit values in different way.
- Specific protocols are needed for each type of media that describe the proper bit patterns to be used, how data is encoded into media signals, and the various qualities of the physical media's attachment interface.
The role of the physical layer is to encode the binary digits that represent data link layer frames into signals and to transmit and receives these signals across the physical media that connect network devices.
Copper cable
Fiber
Wireless
•Definition of Hardware Specifications
•Encoding and Signaling (bit representation)
•Data Transmission and Reception (half duplex, full duplex )
•Topology and Physical Network Design (mesh, ring, bus)
•PDU: bit
