TCP/IP Model

osi-versus-tcpip

TCP/IP Model

TCP/IP Model is also another important referance model in network world. OSI Referance Model was Seven Layered, TCP/IP Model is Four Layered. In common, they model the same thing. But, borders of the Layers of different models, are different.


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Let’s check ech TCP/IP Layer one by one.

Network Interface (Network Access) Layer

Network Interface Layer is the Physical Layer of TCP/IP Model. So, the transmission of bits, cabling are in the responsibility of this Layer. The protocols used in Network Interface Layer of TCP/IP Model are Ethernet, Token Ring, FDDI, Frame Relay, X.25, RS-232 etc.

Network Interface Layer of TCP/IP Model corresponds two Layers of OSI Model. These OSI Layers are Physical Layer and Data-Link Layer.

Internet Layer

The data is transmitted and routed between the source and the destination by the help of this Internet Layer of TCP/IP Model. Internet Layer packs data into data packets known as IP Datagrams, This IP Datagrams contains Source and Destination Addresses. The main protocols used in Internet Layer are IP (Internet Protocol), ARP (Address Resolution Protocol), RARP (Reverse Address Resolution Protocol), ICMP (Internet Control Message Protocol), IGMP (Internet Group Management Protocol) etc.

Transport Layer

Transport Layer provides the Session between end points. It manages the Sessions. Two common Transport Protocols are in this layer like OSI Transport Layer. These Trasport Layer Protocols are TCP (Transmission Control Protocol) and UDP (User Datagram Protocol).

Application Layer

Application Layer defines the Application Layer Protocols and it is the Interface between the user and the Transport Layer. It summarizes the processes that make data intended for the Application. The Protocols used in this Layer are HTTP (Hypertext Transfer Protocol), DNS, DHCP (Dynamic Host Configuration Protocol), FTP (File Transfer Protocol), Telnet, TFTP (Trivial File Transfer Protocol), SNMP (Simple Network Management Protocol), SMTP (Simple Mail Transfer Protocol) etc.

As you see, the Protocols used in a network is the same. Only the Referance Model and its Layers are changing theorically.

TCP Model versus OSI Model

TCP/IP Model combines some of the Layers of OSI and behave like one Layer. Instead of OSI Physical Layer (Layer 1) and Data-Link Layer (Layer 2), TCP/IP Model use Network Interface (Network Access) Layer. Network Layer of OSI is changed as Internet Layer in TCP/IP Model. The Transport Layer is the same as OSI Referance Model. Lastly, TCP/IP Model mix the three Upper Layers of OSI Model, into one Application Layer.


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TCP/IP Model Email Example

Let’s look at these picture from one end to another end. Let’s think about that, a user in a network wants to send an eMail to the other user in another network. How will the data process?


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As you can see above, the data transmission starts from the PC. Beginning with the Application Layer, in each Layer, an additional Header is added and at the media, it is sent with 1s and 0s.


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At the other end, this time the Headers are stripped in each Layer and, pure Data is transmitted to the PC.


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Lesson tags: osi model, tcp/ip
Back to: JNCIA Junos > Network Fundamentals