The TCP/IP Model
TCP/IP model has four layers as in below given diagram
As data is being sent from one computer, it will pass from the top layer to the bottom. On the receiving end, the data will then be rebuilt from the bottom layer to the top.
Each layer a packet of information travels through adds what is called a header
At the receiving end, we would have the reverse process (Headers would be taken away at each layer, until the receiving packet is by itself.)
Since each layer of the TCP/IP model does a unique task separate of the other layers, we refer to the data package at each layer with different names. For instance, the data package at the Application Layer is called a message, while the same data package at the Internet Layer is called a datagram. Review the diagram below for the complete list of names.
Notice that the Transport Layer may have one of two names- a segment or a datagram. If the TCP protocol is being used, it is called a segment. If the UDP protocol is being used, it is called a Datagram.
The data then passes through the Internet Layer onto the Network Access Layer, where a frame is created. Once the data packet leaves this level it is converted into a bitstream of electrical pulses, commonly referred to as 1’s and 0’s.
Finally, you should note that Cisco demands CCNA students to know specific information on the Data Link
The encapsulation process with the OSI model below.
The Data Encapsulation Process summary
1. One computer requests to send data to another over a network.
2. The data message flows through the Application Layer by using a TCP or UDP port to pass onto the internet layer.
3. The data segment obtains logical addressing at the Internet Layer via the IP protocol, and the data is then encapsulated into a datagram.
4. The datagram enters the Network Access Layer, where software will interface with the physical network. A data frame encapsulates the datagram for entry onto the physical network. At the end of the process, the frame is converted to a stream of bits that is then transmitted to the receiving computer.
5. The receiving computer removes the frame, and passes the packet onto the Internet Layer. The Internet Layer will then remove the header information and send the data to the Transport layer. Likewise, the Transport layer removes header information and passes data to the final layer. At this final layer the data is whole again, and can be read by the receiving computer if no errors are present.