> For the complete documentation index, see [llms.txt](https://mudassirs46.gitbook.io/network-fundamentals/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mudassirs46.gitbook.io/network-fundamentals/half-duplex.md). # Half Duplex The device must wait before sending a Frame if it is currently receiving a frame. It can either Send or Receive at a time. (E.g. Walkie-Talkie) * **When Half Duplex is enabled it enables** [**CSMA/CD**](https://app.gitbook.com/@mudassirs46/s/network-fundamentals/~/drafts/-MRZ8l67L5MHnaQIEh9W/csma-cd-carrier-sense-multiple-access-collision-detection) **because one can either send/receive at a time in Half Duplex settings. If however both send at the send time then collision can occur.** * HUB is a Half Duplex device because it is a dumb device & broadcasts all the received frame to all the other ports & if it receiving any frame at the same instance then collisions are bound to happen. Hence, HUB uses Half Duplex with the help of CSMA/CD. * On Full Duplex side you will see Late Collisions / Buffer overloading. * [Autonegotiation](https://app.gitbook.com/@mudassirs46/s/network-fundamentals/~/drafts/-MRZ8l67L5MHnaQIEh9W/autonegotiation) failure leads to [Duplex Mismatch](https://app.gitbook.com/@mudassirs46/s/network-fundamentals/~/drafts/-MRZ8l67L5MHnaQIEh9W/duplex-mismatch) ## Reference: * CCNA 200-301 OCG, Volume 1, Pg. 160 - Wendell Odom. *