--- title: "Compare OSI and TCP/IP models" subject: "Computer Networks and Security" chapter: 1 key: "semester_7/computer_networks_and_security:osi-vs-tcpip" source: https://www.bctengineer.com/q/semester_7/computer_networks_and_security/osi-vs-tcpip site: BCT Engineering --- # Compare OSI and TCP/IP models Computer Networks and Security · Chapter 1: Introduction to Computer Network - Asked in: 2073 Shrawan, 5 marks; 2072 Chaitra, 5 marks; 2071 Shrawan, 6 marks; 2071 Chaitra, 3 marks; year not given (asked 4 times) - Video: [Lec-4: TCP/IP Protocol Suite | Internet Protocol Suite | OSI vs TCP/IP](https://www.youtube.com/watch?v=GfaHdjApnhU) — Gate Smashers - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/computer_networks_and_security/osi-vs-tcpip - Whole chapter: https://www.bctengineer.com/md/semester_7/computer_networks_and_security/chapter-1 ## Question Differentiate between the OSI and TCP/IP reference models. ## Short answer OSI is a seven-layer protocol-independent reference model from ISO; TCP/IP is a four-layer practical model from the US DoD built around Internet protocols. OSI separates session/presentation and data link/physical layers, while TCP/IP merges them. TCP/IP is the actual Internet standard; OSI is mainly for teaching and reference. ## Answer The **OSI model** is a seven-layer, protocol-independent reference model from ISO, while the **TCP/IP model** is a four-layer (sometimes five-layer) practical model built around the protocols of the Internet. ```text OSI TCP/IP +--------------+ | Application | | Presentation | +-------------+ | Session | | Application | +--------------+ +-------------+ | Transport | | Transport | +--------------+ +-------------+ | Network | | Internet | +--------------+ +-------------+ | Data link | | Host-to- | | Physical | | network | +--------------+ +-------------+ ``` | Point | OSI model | TCP/IP model | |---|---|---| | Layers | 7 | 4 (Application, Transport, Internet, Host-to-network) | | Developed by | ISO | US DoD (ARPANET) | | Approach | Model first, protocols later | Protocols first, model later | | Session and presentation | Separate layers | Merged into application layer | | Data link and physical | Separate layers | Merged into host-to-network layer | | Service, interface, protocol | Clearly separated concepts | Not clearly separated | | Transport layer | Connection-oriented only (reliable) | Both: TCP (reliable, connection-oriented) and UDP (unreliable, connectionless) | | Network layer | Both connection-oriented and connectionless | Connectionless only (IP) | | Protocol fit | Protocols are better hidden and easier to replace | Not generic; cannot describe non-TCP/IP stacks well | | Use | Teaching and reference | Actual Internet standard | **Similarities:** both are layered, both have application, transport and network-type layers, and both use packet switching. **Main reason TCP/IP won:** its protocols already worked and were free, while OSI was complex, late and badly timed. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. How many layers do the OSI and TCP/IP models have (as described in the answer)? A. OSI 4, TCP/IP 7 B. OSI 7, TCP/IP 4 C. Both 7 D. OSI 5, TCP/IP 4 Answer: B. OSI has seven layers; TCP/IP has four (Application, Transport, Internet, Host-to-network). (Key point: Layer count) 2. Which statement about how each model was developed is correct? A. OSI: model first, protocols later; TCP/IP: protocols first, model later B. OSI: protocols first; TCP/IP: model first C. Both were made model first D. Both were made protocols first Answer: A. TCP/IP's protocols already existed and the model described them, while OSI defined the model before its protocols. (Key point: Design approach) 3. Which pairing of services is correct? A. OSI network layer: connectionless only; TCP/IP transport: TCP only B. OSI network layer: connection-oriented and connectionless; TCP/IP transport: TCP and UDP C. OSI network layer: connection-oriented only; TCP/IP network: both D. OSI transport: TCP and UDP; TCP/IP network: both Answer: B. OSI's network layer supports both modes, while TCP/IP's Internet layer (IP) is connectionless but its transport layer offers TCP (reliable) and UDP (unreliable). (Key point: Transport and network services) 4. Why did TCP/IP win over OSI in practice? A. OSI had fewer layers B. Its protocols already worked and were free, while OSI was complex, late and badly timed C. TCP/IP was developed by ISO D. OSI had no transport layer Answer: B. TCP/IP had working, free protocols, whereas OSI arrived late and was complex. (Key point: Why TCP/IP won) ## Related in Computer Networks and Security - [Explain OSI model and its layers](https://www.bctengineer.com/question.md?key=semester_7%2Fcomputer_networks_and_security%3Aosi-model-layers) — Computer Networks and Security, chapter 1, asked 2× - [Tasks done at OSI layers (set 2)](https://www.bctengineer.com/question.md?key=semester_7%2Fcomputer_networks_and_security%3Aosi-layer-task-mapping-2) — Computer Networks and Security, chapter 1 - [Functions of physical layer](https://www.bctengineer.com/question.md?key=semester_7%2Fcomputer_networks_and_security%3Aphysical-layer-functions) — Computer Networks and Security, chapter 2 - [Why two transport protocols exist](https://www.bctengineer.com/question.md?key=semester_7%2Fcomputer_networks_and_security%3Awhy-two-transport-protocols) — Computer Networks and Security, chapter 5 ## Related in other subjects - [TCP/IP applications; IPv4 vs IPv6 routing](https://www.bctengineer.com/question.md?key=semester_8%2Finternet_and_intranet%3Atcpip-application-ipv4-ipv6-routing) — Internet and Intranet, chapter 2 - [Compare software models; propose a fourth model](https://www.bctengineer.com/question.md?key=semester_5%2Finstrumentation_ii%3Asw-models-compare-fourth) — Instrumentation II, chapter 9 - [Compare RGB, CMY and HSB models](https://www.bctengineer.com/question.md?key=semester_8%2Fmultimedia_system%3Argb-cmy-hsb-comparison) — Multimedia System, chapter 3 - [SS7 vs OSI; MTP-L2 signal units](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Ass7-vs-osi-mtp2-units) — Telecommunications, chapter 5