While full duplex communication is common on today's modern networks, you can still find half duplex communication as well. For example, if you deploy a hub rather than a switch, the hosts that connect to the hub will need to have the NICs be configured for half duplex. You see, the Ethernet Standard is half duplex. Ethernet is based on CSMA-CD (carrier sense multiple access with collision detection). Wow, i havent used that acronymn in quite a while. I can go into more details, but its going to be quite a long discussion.
When you implement switches (fast ethernet) on your network, the default configutation is going to be is full duplex. Switches allow for sending and receiving at the same time (4 wires instead of using 2).
You can have a mix of half and full duplex communication on a host. If your hosts and network gear is set to auto detect/auto sense, the devices will self configure the ports.
so...basically ,as almost nobody uses Hubs any more,everywhere we see,is the full duplex tech? isn't it a waste of CSMA-CD protocol (effort they made to develop) which they created to control half duplex channels?
Back in the day when Ethernet was over coax cables, half-duplex was a necessity (the comment about CSMA-CD is appropriate here). That changed with ethernet over twisted pair when you could have separate channels for sending/receiving data. Back then, before ethernet could run over twisted pair, ethernet was not suitable for real-time control systems. Arcnet and Token Ring could be (and were) used for deterministic realtime systems. Once ethernet was running on full-duplex switched gear, it became capable of real time (deterministic) behavior, so now it is ubiquitous in industrial control systems which previously would have been interconnected via alternative means.
Yes, what I meant by that is even modern networks today, have legacy equipment scattered throught the network. This is especially the case in large infrastructures where the edge (client connectivity) is either not well managed. I still see forgotten and unmanaged closets with gear from 10 years ago. There are also some other devices, like print devices that just won't break and ate still on the network connected via print servers running half duplex. Of course as time has passed, you don't see this as much lately.
Half-Duplex is still around, due to Legacy Equipment as ITG-JM said. And chances are, people are still running in half-duplex even though they are full-duplex capable due to misunderstanding of how the auto-duplex feature of switches work. And yes, there are still hubs on networks, and they do require us to have half-duplex enabled otherwise work could not get done. I've seen workers hook up their own hubs to switch ports and use them in order to have multiple ports to work on, this obviously produces a problem and helpdesk tickets if a switch was not able to use half-duplex communication.
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