Protocol Data Unit and Encapsulation
For Application data to travel uncorrupted from one host to another, header (or control data), which contain control and adding information is added to the data as it moves down to layer.
The process of adding control information as it passes through the layered model is called Encapsulation.Decapsulation is the process of remaining the extra information and sending only the original application data up to the destination application layer.
Each layer adds control information at each step. The generic term for data at each level is Protocol Data Unit.
But a PDU is different at each layer. A PDU at the internetwork layer is different from the PDU at the transport layer.
Protocol Data Unit on different layer
PDU name Layer
Data Application layer
Segment Transport layer
Packet Internetwork layer
Frame Network Access layer
Bits Physical layer
Comparing the OSI and TCP/IP model
TheTCP/IP model evolved faster than the OSI model and is now more practical in describing network communication functions .The OSI model describes in details functions that occur at the upper layer on the hosts. While networking is largely a function of the lower layer.
The function of the Application layer, Presentation layer and the Session layer of the OSI model are combined into one Application layer in the TCP/IP model. The most networking function resides at the Transport and the Network Layer so they remain individual. TCP protocol operates at the transport layer and the IP protocol operates at the Internet layer. The Data link layer and the Physical layer of the OSI model combine make the Network Access layer of the TCP/IP mode.
OSI Model TCP/IP Model
1. Application layer
Presentation layer Application layer
Session layer
2. Transport layer Transport layer
3. Network layer Intenerwork layer
4. Data link layer Network Access layer
Physical layer
Related posts: