Introduction to OSI Layer
In the beginning the development of networks the bad part was that one vendor’s solution was not compatible with another vendor’s solution. This is where the idea for the OSI model was born, having a layered approach to networks our hardware vendors would design hardware for the network, and others could develop software for the application layer. Using an open model which everyone agrees on means we can build networks that are compatible with each other.
To fix this problem the International Organization for Standardization (ISO) researched different network models and the result is the OSI-model which was released in 1984.
Layers are :
Layer 7 – Application layer
This is the closest layer to the end user. It provides the user interface between the applications. Telnet, FTP, email client (SMTP), HyperText Transfer Protocol (HTTP) are examples of Application layer.
Layer 6 – Presentation layer
This layer ensures the presentation of data, that the communications passing through are in the appropriate form for the recipient. In general, it acts as a translator of the network.
Character code translation: for example, ASCII to EBCDIC.
Data conversion: bit order, CR-CR/LF, integer-floating point, and so on.
Data compression: reduces the number of bits that need to be transmitted on the network.
Data encryption: encrypt data for security purposes. For example, password encryption.
Layer 5 – Session layer
Layer 5 establishes, maintains and ends communication with the receiving device.
Layer 4 – Transport layer
Data is reffered here as a segment. This layer maintains flow control of data and provides for error checking and recovery of data between the devices. The most common example of Transport layer is Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). Data is reffered here as a segment
Layer 3 – Network layer
Data is reffered here as a packet. This layer provides logical addresses which routers will use to determine the path to the destination. In most cases, the logic addresses here means the IP addresses (including source & destination IP addresses).
Layer 2 – Data Link Layer
Data is reffered here as a frame. The Data Link layer formats the message into a data frame, and adds a header containing the hardware destination and source address to it. This header is responsible for finding the next destination device on a local network.
Notice that layer 3 is responsible for finding the path to the last destination (network) but it doesn’t care about who will be the next receiver. It is the Layer 2 that helps data to reach the next destination.
This layer is subdivide into 2 sub-layers: logical link control (LLC) and media access control (MAC).
The LLC functions include:
+ Managing frames to upper and lower layers
+ Error Control
+ Flow control
The MAC sublayer carries the physical address of each device on the network. This address is more commonly called a device’s MAC address. MAC address is a 48 bits address which is burned into the NIC card on the device by its manufacturer.
Layer 1 – Physical layer
Data is send here as a bit. The Physical Layer defines the physical characteristics of the network such as connections, voltage levels and timing.
In the beginning the development of networks the bad part was that one vendor’s solution was not compatible with another vendor’s solution. This is where the idea for the OSI model was born, having a layered approach to networks our hardware vendors would design hardware for the network, and others could develop software for the application layer. Using an open model which everyone agrees on means we can build networks that are compatible with each other.
To fix this problem the International Organization for Standardization (ISO) researched different network models and the result is the OSI-model which was released in 1984.
Layers are :
Layer 7 – Application layer
This is the closest layer to the end user. It provides the user interface between the applications. Telnet, FTP, email client (SMTP), HyperText Transfer Protocol (HTTP) are examples of Application layer.
Layer 6 – Presentation layer
This layer ensures the presentation of data, that the communications passing through are in the appropriate form for the recipient. In general, it acts as a translator of the network.
Character code translation: for example, ASCII to EBCDIC.
Data conversion: bit order, CR-CR/LF, integer-floating point, and so on.
Data compression: reduces the number of bits that need to be transmitted on the network.
Data encryption: encrypt data for security purposes. For example, password encryption.
Layer 5 – Session layer
Layer 5 establishes, maintains and ends communication with the receiving device.
Layer 4 – Transport layer
Data is reffered here as a segment. This layer maintains flow control of data and provides for error checking and recovery of data between the devices. The most common example of Transport layer is Transmission Control Protocol (TCP) and User Datagram Protocol (UDP). Data is reffered here as a segment
Layer 3 – Network layer
Data is reffered here as a packet. This layer provides logical addresses which routers will use to determine the path to the destination. In most cases, the logic addresses here means the IP addresses (including source & destination IP addresses).
Layer 2 – Data Link Layer
Data is reffered here as a frame. The Data Link layer formats the message into a data frame, and adds a header containing the hardware destination and source address to it. This header is responsible for finding the next destination device on a local network.
Notice that layer 3 is responsible for finding the path to the last destination (network) but it doesn’t care about who will be the next receiver. It is the Layer 2 that helps data to reach the next destination.
This layer is subdivide into 2 sub-layers: logical link control (LLC) and media access control (MAC).
The LLC functions include:
+ Managing frames to upper and lower layers
+ Error Control
+ Flow control
The MAC sublayer carries the physical address of each device on the network. This address is more commonly called a device’s MAC address. MAC address is a 48 bits address which is burned into the NIC card on the device by its manufacturer.
Layer 1 – Physical layer
Data is send here as a bit. The Physical Layer defines the physical characteristics of the network such as connections, voltage levels and timing.
No comments:
Post a Comment