The OSI Model we just looked at is just a reference/logical model. The TCP/IP model is a part of the Internet Protocol Suite. This model acts as a communication protocol for computer networks and connects hosts on the Internet. It is a concise version of the OSI Model and comprises four layers in its structure.
- The TCP/IP model was developed prior to the OSI model.
- The TCP/IP model is not exactly similar to the OSI model.
- The TCP/IP model consists of four layers: the application layer, transport layer, network layer, and Internet.
- The first four layers provide physical standards, network interface, internetworking, and transport functions that correspond to the first four layers of the OSI model and these four layers are represented in TCP/IP model by a single layer called the application layer.
- TCP/IP is a hierarchical protocol made up of interactive modules, and each of them provides specific functionality.
Why Another Model?
- Although the OSI reference model is universally recognized, the historical and technical open standard of the Internet is Transmission Control Protocol / Internet Protocol (TCP/IP).
- The TCP/IP reference model and the TCP/IP protocol stack make data communication possible between any two computers, anywhere in the world, at nearly the speed of light.
- The U.S. Department of Defense (DoD) created the TCP/IP reference model because it wanted a network that could survive any conditions, even a nuclear war.
TCP/IP Layers:
- Process/Application Layer
- Host-to-Host/Transport Layer
- Internet Layer
- Network Access/Link Layer
The first layer is the Process layer on the behalf of the sender and Network Access layer on the behalf of the receiver. During this article, we will be talking on the behalf of the receiver.
1. Network Access Layer:
This layer corresponds to the combination of Data Link Layer and Physical Layer of the OSI model. It looks out for hardware addressing and the protocols present in this layer allows for the physical transmission of data.
We just talked about ARP being a protocol of Internet layer, but there is a conflict about declaring it as a protocol of Internet Layer or Network access layer. It is described as residing in layer 3, being encapsulated by layer 2 protocols.
2. Internet Layer:
This layer parallels the functions of OSI’s Network layer. It defines the protocols which are responsible for logical transmission of data over the entire network. The main protocols residing at this layer are : IP, ICMP, ARP.
3. Transport Layer:
This layer is analogous to the transport layer of the OSI model. It is responsible for end-to-end communication and error-free delivery of data. It shields the upper-layer applications from the complexities of data. The two main protocols present in this layer are:
| Feature | TCP | UDP |
| Basis | TRANSMISSION CONTROL PROTOCOL (TCP) | USER DATAGRAM PROTOCOL (UDP) |
| Connection status | Requires an established connection to transmit data (connection should be closed once transmission is complete) | Connectionless protocol with no requirements for opening, maintaining, or terminating a connection |
| Data sequencing | Able to sequence | Unable to sequence |
| Guaranteed delivery | Can guarantee delivery of data to the destination router | Cannot guarantee delivery of data to the destination |
| Retransmission of data | Retransmission of lost packets is possible | No retransmission of lost packets |
| Error checking | Extensive error checking and acknowledgment of data | Basic error checking mechanism using checksums |
| Method of transfer | Data is read as a byte stream; messages are transmitted to segment boundaries | UDP packets with defined boundaries; sent individually and checked for integrity on arrival |
| Speed | Slower than UDP | Faster than TCP |
| Broadcasting | Does not support Broadcasting | Does support Broadcasting |
| Optimal use | Used by HTTPS, HTTP, SMTP, POP, FTP, etc | Video conferencing, streaming, DNS, VoIP, etc |
4. Application Layer:
This layer performs the functions of top three layers of the OSI model: Application, Presentation and Session Layer. It is responsible for node-to-node communication and controls user-interface specifications. Some of the protocols present in this layer are: HTTP, HTTPS, FTP, TFTP, Telnet, SSH, SMTP, SNMP, NTP, DNS, DHCP, NFS, X Window, LPD.