# TCP vs UDP The internet is a **huge global network** made up of millions of computers, servers, routers, and cables. For all these different machines—built by different companies, running different operating systems, and located in different countries—to communicate smoothly, **they must follow common rules**. These rules are called **protocols**. Without rules, data sent from one computer might be misunderstood, lost, duplicated, or arrive in the wrong order. Protocols define **how data is packaged, addressed, transmitted, received, and interpreted** across the network. For example: * **IP (Internet Protocol)** decides **where data should go** * **TCP and UDP** decide **how data is delivered** * **DNS** decides **how names are translated into addresses** * **HTTP/HTTPS** decide **how web data is requested and served** Together, these protocols ensure that when you send a message, open a website, or stream a video, the data reaches the correct destination **reliably, efficiently, and securely**. 👉 In short, **the internet works because everyone follows the same set of rules for sending data**.**What are TCP and UDP** **TCP** and **UDP** are **transport-layer protocols** that decide **how data is sent between computers over a network**. **They control how data travels from one device to another.** ## TCP (Transmission Control Protocol) ### 🔹 What TCP does TCP provides **reliable, ordered, and error-checked delivery** of data. ### Features * Connection-oriented (3-way handshake) * Guarantees data delivery * Maintains correct order * Retransmits lost data * Slower but reliable ### Used in * Websites (HTTP/HTTPS) * Emails * File transfers * APIs --- ## UDP (User Datagram Protocol) ### 🔹 What UDP does UDP sends data **without checking delivery or order**. ### Features * Connectionless * No guarantee of delivery * No retransmission * Very fast * Low overhead ### Used in * Video streaming * Online gaming * Voice calls (VoIP) * Live broadcasts --- ## 🆚 ** TCP vs UDP (Quick Comparison)** | Feature | TCP | UDP | | --- | --- | --- | | Connection | Required | Not required | | Reliability | Guaranteed | Not guaranteed | | Speed | Slower | Faster | | Order | Preserved | Not preserved | | Use case | Accuracy | Speed | --- ## Simple analogy * TCP = registered post (safe & tracked) * UDP = normal post (fast but no tracking) --- ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1769694095354/a4da5f4f-6b6e-4eae-b789-8ff05567edf1.png align="center") 1. ## **When to use TCP** Use TCP (Transmission Control Protocol) **when data integrity, accuracy, and ordered delivery are critical**, such as for web browsing (HTTP/HTTPS), file transfers (FTP), email (SMTP/IMAP), and secure shell (SSH) access. It is ideal for applications that cannot tolerate packet loss or data corruption, ensuring reliable, connection-oriented communication.  **Key Scenarios for Using TCP:** * **Web Browsing (HTTP/HTTPS):** Essential for loading webpages correctly, ensuring no data is missing or corrupted. * **File Transfers (FTP/SFTP):** Ensures files (like software downloads) are transmitted accurately without errors. * **Email (SMTP, POP, IMAP):** Guarantees messages and attachments are delivered fully. * **Remote Administration (SSH, Telnet):** Requires a reliable, persistent, and ordered stream of data for commands. * **Database Connections:** Crucial for applications where data accuracy is paramount, such as SQL queries.  **Why Choose TCP?** * **Reliability:** TCP provides error checking, retransmission of lost packets, and guarantees data delivery. * **Ordered Delivery:** It ensures packets arrive in the correct sequence. * **Connection-Oriented:** A stable session is established before data is exchanged.  **When Not to Use TCP:** Avoid TCP for real-time, low-latency applications like live voice/video streaming or online gaming, where speed is more important than losing a few packets. In those cases, [**UDP**](https://www.geeksforgeeks.org/computer-networks/when-is-udp-preferred-to-tcp/) is preferred ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1769694635222/74718476-af3a-4f97-bbdc-fc00840d4bda.png align="center") ## **When to use UDP** **UDP (User Datagram Protocol)** should be used when **speed and low latency matter more than perfect reliability**. Use UDP when it’s okay to lose some data, but not okay to be slow. ## Best situations to use UDP ### 1️⃣ Live video & audio streaming * Zoom, Google Meet, YouTube Live * Missing 1–2 frames is better than freezing 👉 UDP avoids delays caused by retransmissions. --- ### 2️⃣ Online gaming * Multiplayer games need **real-time updates** * Late data is useless 👉 Speed > accuracy. --- ### 3️⃣ Voice over IP (VoIP) * Internet calls * Small packet loss is unnoticeable * Delay is very noticeable --- ### 4️⃣ Real-time sensors & IoT * Weather sensors * GPS tracking * Live telemetry 👉 Data is continuously updated. --- ### 5️⃣ Broadcasting & Multicasting * Live sports * TV streaming * One sender → many receivers 👉 UDP is efficient for this. --- ### 6️⃣ Simple request–response protocols Examples: * **DNS** * **DHCP** * **SNMP** 👉 Small, fast messages. --- ## Common real-world examples of TCP vs UDP When NOT to use UDP * File downloads * Emails * Banking transactions * Web pages where accuracy matters Use **TCP** instead. --- ## Simple analogy * UDP = live phone call (some words may drop) * TCP = email or courier (everything must arrive) --- ## **Common real-world examples of TCP vs UDP** TCP (Transmission Control Protocol) and UDP (User Datagram Protocol) serve different needs: TCP provides reliable, ordered, and error-checked delivery (ideal for accuracy), while UDP offers fast, connectionless, and lightweight transmission (ideal for speed). Common TCP examples include **web browsing (HTTP/HTTPS), email (SMTP), and file transfers (FTP)**. UDP is used for real-time applications like online gaming, VoIP, and live video streaming.  **Real-World Examples of TCP (Reliability Focus)**  * **Web Browsing (HTTP/HTTPS):** When loading web pages, all data must arrive accurately to display properly. * **File Transfer (FTP, SFTP):** Ensuring files (like documents or software downloads) are not corrupted during transfer. * **Email (SMTP, IMAP, POP):** Guaranteeing that an email is delivered exactly as sent. * **Remote Desktop/SSH:** Securely managing remote servers where command accuracy is critical. * **Streaming Content (Netflix/YouTube):** Using buffering to ensure high-quality playback, prioritizing complete data over real-time speed.  **Real-World Examples of UDP (Speed/Latency Focus)**  * **Online Gaming (Fortnite, Call of Duty):** Fast updates are more important than receiving every single packet; if a packet is lost, the game simply waits for the next update. * **Video Conferencing (Zoom, Skype, WhatsApp):** Real-time, two-way communication requires low latency; occasional minor audio/video glitches are better than high lag. * **Voice over IP (VoIP):** Similar to video conferencing, speed is prioritized for smooth audio. * **DNS (Domain Name System):** Resolving website names to IP addresses quickly to initiate fast web browsing. * **Live Sports Streaming:** Real-time data delivery is more important than perfect picture quality, preferring lower latency.  **Key Differences Summary** * [**TCP**](https://www.google.com/search?q=TCP&sca_esv=e8f5b2d100cbb45b&biw=1280&bih=551&aic=0&sxsrf=ANbL-n7qfzMh3FvLL56g3juM-Vll8DRoeg%3A1769694464656&ei=AGV7adHgJ5-OseMPlvOD4QQ&ved=2ahUKEwi4wfDZ87CSAxW_RmcHHSauPa0QgK4QegQICRAB&uact=5&oq=Common+real-world+examples+of+TCP+vs+UDP%0D%0A%0D%0A&gs_lp=Egxnd3Mtd2l6LXNlcnAiKkNvbW1vbiByZWFsLXdvcmxkIGV4YW1wbGVzIG9mIFRDUCB2cyBVRFAKCjIHECMYJxjqAjIHECMYJxjqAjIHECMYJxjqAjINECMY8AUYJxjJAhjqAjIHECMYJxjqAjINECMY8AUYJxjJAhjqAjIHECMYJxjqAjIHECMYJxjqAjIHECMYJxjqAjIHECMYJxjqAjIXEAAYgAQYkQIYtAIY5wYYigUY6gLYAQEyFxAAGIAEGJECGLQCGOcGGIoFGOoC2AEBMhcQABiABBiRAhi0AhjnBhiKBRjqAtgBATIXEAAYgAQYkQIYtAIY5wYYigUY6gLYAQEyFxAAGIAEGJECGLQCGOcGGIoFGOoC2AEBMhcQABiABBiRAhi0AhjnBhiKBRjqAtgBAUilD1DiBVjiBXABeAGQAQCYAQCgAQCqAQC4AQPIAQD4AQH4AQKYAgGgAg6oAhCYAw7xBca_nIhtmGutugYGCAEQARgBkgcBMaAHALIHALgHAMIHAzMtMcgHCYAIAA&sclient=gws-wiz-serp&mstk=AUtExfDUVRjnI3YQxdRzjDqKAhjfFA3vRQ_Sf3Md0c1JvPZlcDRmYQD7aUymv3WVFZSDXLcZRZ8GWf4HN5pYqWdUghuwXEizk8ZVttlaTOgpjzVgwrRENWg3CeogwX5r0gOLLlQtmbyaatidEDbaeuJrh_3D-3HEwOQ7zkoOvNX7U264DMqzkqOkmIs-Sp7hwXrqofiNekDZwZprYhCRUMURpX111cnt8uzzekUFDEq0-EHCxdLvVHop7k37uEDNQx1DUpx4kpPv5TB_gPPnsGPakleRyBIjEUWAa1tMQR-4xvboPJL1NWf_TXBSUzNRhsmF5MocPxEG-vSx4W2FY9ITibTByaXVGtGRsff_Bal8yFzy08eXHYxBlSZdW9ByYQqw5i6nidJHswbm5wTor7U0enYqk2ngtymxD4UTtGrxAmgIzhwr9l1FkT09AtGLO7tb&csui=3)**:** Connection-oriented, retransmits lost packets, slower. * [**UDP**](https://www.google.com/search?q=UDP&sca_esv=e8f5b2d100cbb45b&biw=1280&bih=551&aic=0&sxsrf=ANbL-n7qfzMh3FvLL56g3juM-Vll8DRoeg%3A1769694464656&ei=AGV7adHgJ5-OseMPlvOD4QQ&ved=2ahUKEwi4wfDZ87CSAxW_RmcHHSauPa0QgK4QegQICRAD&uact=5&oq=Common+real-world+examples+of+TCP+vs+UDP%0D%0A%0D%0A&gs_lp=Egxnd3Mtd2l6LXNlcnAiKkNvbW1vbiByZWFsLXdvcmxkIGV4YW1wbGVzIG9mIFRDUCB2cyBVRFAKCjIHECMYJxjqAjIHECMYJxjqAjIHECMYJxjqAjINECMY8AUYJxjJAhjqAjIHECMYJxjqAjINECMY8AUYJxjJAhjqAjIHECMYJxjqAjIHECMYJxjqAjIHECMYJxjqAjIHECMYJxjqAjIXEAAYgAQYkQIYtAIY5wYYigUY6gLYAQEyFxAAGIAEGJECGLQCGOcGGIoFGOoC2AEBMhcQABiABBiRAhi0AhjnBhiKBRjqAtgBATIXEAAYgAQYkQIYtAIY5wYYigUY6gLYAQEyFxAAGIAEGJECGLQCGOcGGIoFGOoC2AEBMhcQABiABBiRAhi0AhjnBhiKBRjqAtgBAUilD1DiBVjiBXABeAGQAQCYAQCgAQCqAQC4AQPIAQD4AQH4AQKYAgGgAg6oAhCYAw7xBca_nIhtmGutugYGCAEQARgBkgcBMaAHALIHALgHAMIHAzMtMcgHCYAIAA&sclient=gws-wiz-serp&mstk=AUtExfDUVRjnI3YQxdRzjDqKAhjfFA3vRQ_Sf3Md0c1JvPZlcDRmYQD7aUymv3WVFZSDXLcZRZ8GWf4HN5pYqWdUghuwXEizk8ZVttlaTOgpjzVgwrRENWg3CeogwX5r0gOLLlQtmbyaatidEDbaeuJrh_3D-3HEwOQ7zkoOvNX7U264DMqzkqOkmIs-Sp7hwXrqofiNekDZwZprYhCRUMURpX111cnt8uzzekUFDEq0-EHCxdLvVHop7k37uEDNQx1DUpx4kpPv5TB_gPPnsGPakleRyBIjEUWAa1tMQR-4xvboPJL1NWf_TXBSUzNRhsmF5MocPxEG-vSx4W2FY9ITibTByaXVGtGRsff_Bal8yFzy08eXHYxBlSZdW9ByYQqw5i6nidJHswbm5wTor7U0enYqk2ngtymxD4UTtGrxAmgIzhwr9l1FkT09AtGLO7tb&csui=3)**:** Connectionless, no retransmission, faster.  ## **What is HTTP and where it fits** #### What is HTTP? **HTTP (Hyper Text Transfer Protocol)** is a **set of rules** that defines **how web clients and web servers communicate**. **HTTP is the language used by browsers and servers to talk on the web.** ## What HTTP Does HTTP defines: * How a **request** is sent (GET, POST, etc.) * How a **response** is returned * Status codes (200, 404, 500) * Headers and body structure Example: ```plaintext Browser → HTTP Request → Server Browser ← HTTP Response ← Server ``` --- ## Where HTTP Fits in the Internet Stack HTTP does **not send data itself**. It sits **on top of other protocols**. ```plaintext Application Layer → HTTP / HTTPS Transport Layer → TCP (or QUIC for HTTP/3) Internet Layer → IP Network Layer → Ethernet / Wi-Fi ``` 👉 HTTP focuses on **what is being sent**, not **how it physically travels**. --- ## HTTP vs HTTPS * **HTTP** → data in plain text * **HTTPS** → HTTP + TLS encryption (secure) Modern web always uses **HTTPS**. --- ## Where HTTP is used * Websites * REST APIs * Mobile apps * Microservices --- ## Simple analogy * HTTP = language of conversation * TCP = delivery service * IP = address system --- ![](https://cdn.hashnode.com/res/hashnode/image/upload/v1769695595720/ab6e844f-d319-42b6-821a-fddfbdb4ff2a.png align="center") ## **Relationship between TCP and HTTP** An HTTP request flows over a TCP connection **by first establishing a reliable, connection-oriented tunnel via a three-way handshake (SYN, SYN-ACK, ACK)**. Once connected, the client sends HTTP data (request line, headers, body) as a stream of bytes through this TCP socket. The server processes this request and sends back a response, utilizing the same TCP connection.  **Key Aspects of the HTTP/TCP Flow:** * **Connection Establishment:** Before any data is sent, the browser/client initiates a TCP connection with the server (usually on port 80 for HTTP or 443 for HTTPS). * **Data Transmission:** The HTTP request (e.g., `GET / HTTP/1.1`) is transmitted in TCP packets, which are guaranteed to arrive in order and without errors. * **Packetization:** The HTTP request data is broken into segments, transmitted across the network, and reassembled at the destination. * **Connection Persistence:** Modern HTTP (1.1+) uses persistent connections to reuse the same TCP connection for multiple requests, reducing latency. * **Closing the Connection:** The connection is either closed by the client/server after the response is complete or kept open for subsequent requests.  **Steps in the Flow:**  1. [**DNS Lookup**](https://www.google.com/search?sca_esv=e8f5b2d100cbb45b&sxsrf=ANbL-n7i84u265Bfb410LNI5NsjlaS-2TQ%3A1769695614148&q=DNS+Lookup&source=lnms&fbs=ADc_l-aN0CWEZBOHjofHoaMMDiKpaEWjvZ2Py1XXV8d8KvlI3izfzqgn7395CNCvYdZRuZ4-lOsJlglncpOd_-CGga6cOLqDKZIowtVXUSv9JiBkrDj_EVKMNnAlL9U6nYgzJP4iv6sQzj8tIFPpc0hvgoc4YumyWxmscKDKsCQfl0vdGvj741GEr57TdBxmmZqHP29jgv3juYo7vuOEF-nTzHWzB5uvq5uZPCg39rVv-k8Le2AUqKg&sa=X&ved=2ahUKEwiAhr319bCSAxVI1DgGHfs0JnkQgK4QegQIBhAB&biw=1280&bih=551&dpr=1.5&aic=0&mstk=AUtExfD2wX0ZfHJIS3I2glLg9TMT8SPCCCfNWwvehT6o307Or44dvx_X1pWo7tJv-_2zMTvta88WDlDYbrz_GMY8KJN-pffwgCcYzoi_NLD_90ku5NSp8URxTZX8txcpe5DbV50etU1mUc-KFQ1nAyuHXAYzIXWPGIS8rXMNRY2lG7E4FOe2s27tQ7-ByE0iMD5r-e3CCUtZvRJ6udqfRwlYPkFjtXFySGooAlu8AvJm95bFox8aLoc5O2sET0bMmmobolsEeykud24Q7fdHU9nQQjIZ7HsFtzKefD7kjtpnesyTqLEXV_ZcbII7HqovYjWXjlvpwTweH0s3SkceV4y4d2kVnwk_16xc9YUW4zuIeVE7vzi3RfM0TWrrv_041EVzK_VjBFaaq-FJrMzJ_ABocA8IznePC1zPLSxL9vRSdSBOiTR29mswbIGtPTp-S1b-&csui=3)**:** The browser resolves the URL to an IP address. 2. [**TCP Handshake**](https://www.google.com/search?sca_esv=e8f5b2d100cbb45b&sxsrf=ANbL-n7i84u265Bfb410LNI5NsjlaS-2TQ%3A1769695614148&q=TCP+Handshake&source=lnms&fbs=ADc_l-aN0CWEZBOHjofHoaMMDiKpaEWjvZ2Py1XXV8d8KvlI3izfzqgn7395CNCvYdZRuZ4-lOsJlglncpOd_-CGga6cOLqDKZIowtVXUSv9JiBkrDj_EVKMNnAlL9U6nYgzJP4iv6sQzj8tIFPpc0hvgoc4YumyWxmscKDKsCQfl0vdGvj741GEr57TdBxmmZqHP29jgv3juYo7vuOEF-nTzHWzB5uvq5uZPCg39rVv-k8Le2AUqKg&sa=X&ved=2ahUKEwiAhr319bCSAxVI1DgGHfs0JnkQgK4QegQIBhAD&biw=1280&bih=551&dpr=1.5&aic=0&mstk=AUtExfD2wX0ZfHJIS3I2glLg9TMT8SPCCCfNWwvehT6o307Or44dvx_X1pWo7tJv-_2zMTvta88WDlDYbrz_GMY8KJN-pffwgCcYzoi_NLD_90ku5NSp8URxTZX8txcpe5DbV50etU1mUc-KFQ1nAyuHXAYzIXWPGIS8rXMNRY2lG7E4FOe2s27tQ7-ByE0iMD5r-e3CCUtZvRJ6udqfRwlYPkFjtXFySGooAlu8AvJm95bFox8aLoc5O2sET0bMmmobolsEeykud24Q7fdHU9nQQjIZ7HsFtzKefD7kjtpnesyTqLEXV_ZcbII7HqovYjWXjlvpwTweH0s3SkceV4y4d2kVnwk_16xc9YUW4zuIeVE7vzi3RfM0TWrrv_041EVzK_VjBFaaq-FJrMzJ_ABocA8IznePC1zPLSxL9vRSdSBOiTR29mswbIGtPTp-S1b-&csui=3)**:** A three-way connection is established (SYN →right arrow→ SYN-ACK →right arrow→ ACK). 3. [**HTTP Request**](https://www.google.com/search?sca_esv=e8f5b2d100cbb45b&sxsrf=ANbL-n7i84u265Bfb410LNI5NsjlaS-2TQ%3A1769695614148&q=HTTP+Request&source=lnms&fbs=ADc_l-aN0CWEZBOHjofHoaMMDiKpaEWjvZ2Py1XXV8d8KvlI3izfzqgn7395CNCvYdZRuZ4-lOsJlglncpOd_-CGga6cOLqDKZIowtVXUSv9JiBkrDj_EVKMNnAlL9U6nYgzJP4iv6sQzj8tIFPpc0hvgoc4YumyWxmscKDKsCQfl0vdGvj741GEr57TdBxmmZqHP29jgv3juYo7vuOEF-nTzHWzB5uvq5uZPCg39rVv-k8Le2AUqKg&sa=X&ved=2ahUKEwiAhr319bCSAxVI1DgGHfs0JnkQgK4QegQIBhAH&biw=1280&bih=551&dpr=1.5&aic=0&mstk=AUtExfD2wX0ZfHJIS3I2glLg9TMT8SPCCCfNWwvehT6o307Or44dvx_X1pWo7tJv-_2zMTvta88WDlDYbrz_GMY8KJN-pffwgCcYzoi_NLD_90ku5NSp8URxTZX8txcpe5DbV50etU1mUc-KFQ1nAyuHXAYzIXWPGIS8rXMNRY2lG7E4FOe2s27tQ7-ByE0iMD5r-e3CCUtZvRJ6udqfRwlYPkFjtXFySGooAlu8AvJm95bFox8aLoc5O2sET0bMmmobolsEeykud24Q7fdHU9nQQjIZ7HsFtzKefD7kjtpnesyTqLEXV_ZcbII7HqovYjWXjlvpwTweH0s3SkceV4y4d2kVnwk_16xc9YUW4zuIeVE7vzi3RfM0TWrrv_041EVzK_VjBFaaq-FJrMzJ_ABocA8IznePC1zPLSxL9vRSdSBOiTR29mswbIGtPTp-S1b-&csui=3)**:** The browser sends the formatted HTTP request (method, headers, body). 4. [**Server Processing**](https://www.google.com/search?sca_esv=e8f5b2d100cbb45b&sxsrf=ANbL-n7i84u265Bfb410LNI5NsjlaS-2TQ%3A1769695614148&q=Server+Processing&source=lnms&fbs=ADc_l-aN0CWEZBOHjofHoaMMDiKpaEWjvZ2Py1XXV8d8KvlI3izfzqgn7395CNCvYdZRuZ4-lOsJlglncpOd_-CGga6cOLqDKZIowtVXUSv9JiBkrDj_EVKMNnAlL9U6nYgzJP4iv6sQzj8tIFPpc0hvgoc4YumyWxmscKDKsCQfl0vdGvj741GEr57TdBxmmZqHP29jgv3juYo7vuOEF-nTzHWzB5uvq5uZPCg39rVv-k8Le2AUqKg&sa=X&ved=2ahUKEwiAhr319bCSAxVI1DgGHfs0JnkQgK4QegQIBhAJ&biw=1280&bih=551&dpr=1.5&aic=0&mstk=AUtExfD2wX0ZfHJIS3I2glLg9TMT8SPCCCfNWwvehT6o307Or44dvx_X1pWo7tJv-_2zMTvta88WDlDYbrz_GMY8KJN-pffwgCcYzoi_NLD_90ku5NSp8URxTZX8txcpe5DbV50etU1mUc-KFQ1nAyuHXAYzIXWPGIS8rXMNRY2lG7E4FOe2s27tQ7-ByE0iMD5r-e3CCUtZvRJ6udqfRwlYPkFjtXFySGooAlu8AvJm95bFox8aLoc5O2sET0bMmmobolsEeykud24Q7fdHU9nQQjIZ7HsFtzKefD7kjtpnesyTqLEXV_ZcbII7HqovYjWXjlvpwTweH0s3SkceV4y4d2kVnwk_16xc9YUW4zuIeVE7vzi3RfM0TWrrv_041EVzK_VjBFaaq-FJrMzJ_ABocA8IznePC1zPLSxL9vRSdSBOiTR29mswbIGtPTp-S1b-&csui=3)**:** The server receives, parses, and processes the request. 5. [**HTTP Response**](https://www.google.com/search?sca_esv=e8f5b2d100cbb45b&sxsrf=ANbL-n7i84u265Bfb410LNI5NsjlaS-2TQ%3A1769695614148&q=HTTP+Response&source=lnms&fbs=ADc_l-aN0CWEZBOHjofHoaMMDiKpaEWjvZ2Py1XXV8d8KvlI3izfzqgn7395CNCvYdZRuZ4-lOsJlglncpOd_-CGga6cOLqDKZIowtVXUSv9JiBkrDj_EVKMNnAlL9U6nYgzJP4iv6sQzj8tIFPpc0hvgoc4YumyWxmscKDKsCQfl0vdGvj741GEr57TdBxmmZqHP29jgv3juYo7vuOEF-nTzHWzB5uvq5uZPCg39rVv-k8Le2AUqKg&sa=X&ved=2ahUKEwiAhr319bCSAxVI1DgGHfs0JnkQgK4QegQIBhAL&biw=1280&bih=551&dpr=1.5&aic=0&mstk=AUtExfD2wX0ZfHJIS3I2glLg9TMT8SPCCCfNWwvehT6o307Or44dvx_X1pWo7tJv-_2zMTvta88WDlDYbrz_GMY8KJN-pffwgCcYzoi_NLD_90ku5NSp8URxTZX8txcpe5DbV50etU1mUc-KFQ1nAyuHXAYzIXWPGIS8rXMNRY2lG7E4FOe2s27tQ7-ByE0iMD5r-e3CCUtZvRJ6udqfRwlYPkFjtXFySGooAlu8AvJm95bFox8aLoc5O2sET0bMmmobolsEeykud24Q7fdHU9nQQjIZ7HsFtzKefD7kjtpnesyTqLEXV_ZcbII7HqovYjWXjlvpwTweH0s3SkceV4y4d2kVnwk_16xc9YUW4zuIeVE7vzi3RfM0TWrrv_041EVzK_VjBFaaq-FJrMzJ_ABocA8IznePC1zPLSxL9vRSdSBOiTR29mswbIGtPTp-S1b-&csui=3)**:** The server sends back the requested data. 6. [**Connection Closure/Re-use**](https://www.google.com/search?sca_esv=e8f5b2d100cbb45b&sxsrf=ANbL-n7i84u265Bfb410LNI5NsjlaS-2TQ%3A1769695614148&q=Connection+Closure%2FRe-use&source=lnms&fbs=ADc_l-aN0CWEZBOHjofHoaMMDiKpaEWjvZ2Py1XXV8d8KvlI3izfzqgn7395CNCvYdZRuZ4-lOsJlglncpOd_-CGga6cOLqDKZIowtVXUSv9JiBkrDj_EVKMNnAlL9U6nYgzJP4iv6sQzj8tIFPpc0hvgoc4YumyWxmscKDKsCQfl0vdGvj741GEr57TdBxmmZqHP29jgv3juYo7vuOEF-nTzHWzB5uvq5uZPCg39rVv-k8Le2AUqKg&sa=X&ved=2ahUKEwiAhr319bCSAxVI1DgGHfs0JnkQgK4QegQIBhAN&biw=1280&bih=551&dpr=1.5&aic=0&mstk=AUtExfD2wX0ZfHJIS3I2glLg9TMT8SPCCCfNWwvehT6o307Or44dvx_X1pWo7tJv-_2zMTvta88WDlDYbrz_GMY8KJN-pffwgCcYzoi_NLD_90ku5NSp8URxTZX8txcpe5DbV50etU1mUc-KFQ1nAyuHXAYzIXWPGIS8rXMNRY2lG7E4FOe2s27tQ7-ByE0iMD5r-e3CCUtZvRJ6udqfRwlYPkFjtXFySGooAlu8AvJm95bFox8aLoc5O2sET0bMmmobolsEeykud24Q7fdHU9nQQjIZ7HsFtzKefD7kjtpnesyTqLEXV_ZcbII7HqovYjWXjlvpwTweH0s3SkceV4y4d2kVnwk_16xc9YUW4zuIeVE7vzi3RfM0TWrrv_041EVzK_VjBFaaq-FJrMzJ_ABocA8IznePC1zPLSxL9vRSdSBOiTR29mswbIGtPTp-S1b-&csui=3)**:** The connection is terminated or reused for further requests.  ## **Relationship between TCP and HTTP** **HTTP and TCP work together**, but they do **different jobs** in the internet stack. HTTP defines *what* is sent, TCP defines *how* it is delivered reliably. ## Where They Fit (Layered View) ```plaintext Application Layer → HTTP Transport Layer → TCP Internet Layer → IP ``` * **HTTP** sits at the **application layer** * **TCP** sits at the **transport layer** HTTP **depends on TCP** to move its data. --- ## How HTTP Uses TCP (Step-by-Step) 1. Browser wants a web page 2. **TCP connection is established** (3-way handshake) 3. **HTTP request** is sent over that TCP connection 4. Server sends **HTTP response** 5. TCP ensures: * Data arrives * Data is in order * Lost packets are retransmitted 6. Connection is closed or reused --- ## Why HTTP Needs TCP TCP provides: * **Reliability** (no lost data) * **Correct order** * **Error detection** * **Flow control** Web pages must load **correctly**, not partially—so TCP is ideal. --- ## What HTTP does NOT do HTTP does **not**: * Handle packet loss * Guarantee delivery * Manage connections That’s **TCP’s job**. --- ## HTTP over TCP vs HTTP over UDP * **HTTP/1.1 & HTTP/2** → use **TCP** * **HTTP/3** → uses **QUIC (built on UDP)** for lower latency --- ## Simple analogy * HTTP = message content * TCP = reliable courier * IP = address system