Suggest an editImprove this articleRefine the answer for “Why is UDP called "unreliable"?”. Your changes go to moderation before they’re published.Approval requiredContentWhat you’re changing🇺🇸EN🇺🇦UAPreviewTitle (EN)Short answer (EN)**UDP is called "unreliable"** because **it does not guarantee data delivery and does not control the transmission process in any way**. **Key point:** UDP sends data and does not check whether it arrived.Shown above the full answer for quick recall.Answer (EN)Image**UDP is called "unreliable"** because **it does not guarantee data delivery and does not control the transmission process in any way**. More simply: **UDP sends data and does not check whether it arrived**. --- ## What exactly makes UDP "unreliable" ### 1. **No delivery acknowledgments** UDP: - **does not wait for an ACK** - does not know whether the receiver got the message If a packet is lost: - the sender **never finds out** --- ### 2. **No retransmission** UDP: - **does not resend** lost packets - does not try to recover the data Once lost, it is lost forever. --- ### 3. **No order guarantee** UDP: - does not number messages - does not assemble them in the correct sequence Messages can arrive: - in a different order - or not arrive at all --- ### 4. **No congestion control** UDP: - does not reduce speed under network congestion - may keep sending data This can: - worsen congestion - lead to packet loss --- ### 5. **No flow control** UDP: - does not account for whether the receiver can keep up with processing the data - may "flood" the application with messages --- ## What UDP does still do Important. UDP is **not entirely "irresponsible"**: - it preserves **message boundaries** - it checks basic integrity (checksum) - it delivers data on a **best effort** basis But: - if something goes wrong, UDP **does not fix the situation** --- ## Why this is done on purpose UDP is **deliberately simple** because that gives: - minimal latency - minimal overhead - predictable delivery time For many applications, this matters **more than reliability**. --- ## Where "unreliability" is an advantage UDP fits well when: - reaction speed matters - losses are acceptable Examples: - voice communication - real-time video - online games - DNSFor the reviewerNote to the moderator (optional)Visible only to the moderator. Helps review go faster.