Half duplex

As explained in Acing the CCNA Exam: Volume 2 Advanced Networking and Security

Half-duplex is a communication mode in which transmission can occur in both directions but only one device transmits at a time.

Half-duplex communication allows transmission in both directions, but only one device can transmit at a time. Wireless LANs use this mode because devices share an unbounded medium; simultaneous transmissions can collide. section 18.1.1

Wireless devices contend for airtime by listening before transmitting. CSMA/CA makes a device wait when the channel is busy, then transmit when it senses a free channel; simultaneous transmissions can still require retransmission. section 18.1.1

Key networking contrasts:

• A wireless device’s signals can reach all devices within sufficient range, resembling frames flooded through an Ethernet hub. section 18.1.1
• Wireless half-duplex operation helps explain why wireless networks often do not match the speeds of switched Ethernet operating in full-duplex mode. section 18.1.1

Figure 18.3 The CSMA/CA process. To avoid collisions, a device will listen to ensure the channel is free before transmitting a frame.

Trace the simplified CSMA/CA sequence: listen, wait if busy, and transmit when the channel is free. section 18.1.1

How Acing the CCNA Exam: Volume 2 Advanced Networking and Security covers it

How deep it goes

Defines one-at-a-time transmission and explains CSMA/CA, collisions, and retransmission through a simplified process.

Examples

Uses wireless devices, an Ethernet hub analogy, and the CSMA/CA listen-before-transmit sequence.

What you can do after

Evaluate wireless performance and explain airtime contention, collisions, and retransmissions.

How it connects

Connects wireless LANs with shared media, CSMA/CA, collisions, Ethernet hubs, CSMA/CD, and full-duplex switching.

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Also explained in

• 

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  Acing the CCNA Exam: Volume 1 Fundamentals and ProtocolsHalf duplex is a communication mode in which an interface cannot transmit and receive simultaneously and must wait for the medium to become available.

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Related concepts

• networkused by · A network is a system of connected entities and links that enables communication or represents relationships among those entities.
• csma/cdused by · CSMA/CD is a shared-medium access method in which devices sense the channel, transmit when it is idle, and detect collisions during transmission.
• full duplexcontrasts with · Full duplex is a communication mode in which both endpoints can transmit and receive independently and simultaneously.

This explainer was generated by Manning's knowledge graph from the text of Acing the CCNA Exam: Volume 2 Advanced Networking and Security. The section links point to the parts of the book it draws on.