Suggest an editImprove this articleRefine the answer for “How does OSI differ from TCP/IP?”. Your changes go to moderation before they’re published.Approval requiredContentWhat you’re changing🇺🇸EN🇺🇦UAPreviewTitle (EN)Short answer (EN)**OSI** is a seven-layer theoretical model created to standardize networks, while **TCP/IP** is a four-layer practical model that the modern internet is built on. **Key point:** OSI explains how a network should work, while TCP/IP shows how it actually works.Shown above the full answer for quick recall.Answer (EN)Image## **Short answer for an interview** > **OSI is a 7-layer theoretical model created to standardize networks.** > **TCP/IP is a 4-layer practical model that the modern internet is built on.** > **OSI explains how things** ***should*** **work; TCP/IP shows how they** ***actually work*****.** Now, a detailed breakdown. --- ## **1. Number of layers** | OSI | TCP/IP | |---|---| | **7 layers** | **4 layers** | | Splits functions in detail | Combines similar functions | **OSI layers:** 1. Physical 2. Data Link 3. Network 4. Transport 5. Session 6. Presentation 7. Application **TCP/IP layers:** 1. Network Access 2. Internet 3. Transport 4. Application --- ## **2. Theoretical vs. practical model** #### **OSI - a theoretical model** - created for standardization - almost never used "as is" - helps in learning networks - used for analysis and diagnostics #### **TCP/IP - a practical model** - the internet runs on it - supported by all OSes and devices - standardized by the IETF - describes real protocols --- ## **3. OSI layers 5 and 6 are absent in TCP/IP** TCP/IP has **no separate Session and Presentation** layers. Their functions are merged into the Application Layer. Examples: - encryption (TLS) - encoding (UTF-8, MIME) - session management (cookies, HTTP sessions) These functions sit between the application and the transport layer, but the TCP/IP model does not separate them into distinct layers. --- ## **4. Mapping between OSI and TCP/IP layers** | OSI | TCP/IP | |---|---| | Application | Application | | Presentation | Application | | Session | Application | | Transport | Transport | | Network | Internet | | Data Link | Network Access | | Physical | Network Access | --- ## **5. Development: who created it and why** #### **OSI** - developed by ISO - goal: to unify networks from different vendors - focused on standardization #### **TCP/IP** - developed by DARPA - goal: to build a resilient, working network (later the internet) - focused on practice and operation --- ## **6. Flexibility and universality** #### OSI Strictly separates layers → easier to explain and teach. #### TCP/IP Less formal → easier to implement and adapt. --- ## **7. Set of protocols** #### OSI Protocols existed (CLNP), but **never gained wide adoption**. #### TCP/IP The whole model is built on **specific protocols**, for example: - IP - TCP - UDP - DNS - HTTP - ICMP - DHCP This model effectively became the foundation of the internet. --- ## **8. Real-world use** - **TCP/IP** - used *all the time, everywhere* - **OSI** - mostly for teaching, network engineering, and describing how layers interact Still, OSI is more convenient for diagnostics: "Where's the problem? At L1, L2, or L3?" --- ## **Ready answer for an interview (ideal)** > **OSI is a seven-layer reference model created to describe network interaction. It is theoretical and is used for teaching and analysis.** > **TCP/IP is a four-layer practical model that the internet is built on. It combines the OSI layers and describes the real protocol stack: HTTP, TCP, IP, Ethernet, and so on.** > **The main differences: the number of layers, practical applicability, and how functions are segmented.** --- ## **Cheat sheet (5 seconds)** - OSI - 7 layers, theoretical. - TCP/IP - 4 layers, practical. - OSI = we study it, TCP/IP = we use it. - TCP/IP has no Session or Presentation. - TCP/IP describes real protocols (IP, TCP, UDP).For the reviewerNote to the moderator (optional)Visible only to the moderator. Helps review go faster.