Can the devices want to send data at the same time?
Will the devices send the data at the same time ?
the idea is simple. Be it high speed or LTE or any type of communication
If the technology is using packet switched network- Ethernet
the transmission link has a maximum bandwidth.
This dictates how much data can traverse through the data per instance of time.
Thus if more than a certain amout of data is transmitted then it results in collission, retransmissions and this reduces the performance of the system.
Can the devices send at different frequencies.
For that, first of all the cable should support different frequencies of data through the channel (which is not the case for eg. You cannot send any frequency on an optical fiber) which is generally used in high speed communications
But asssuming that it does, the switches need to be equipped with to listen at different frequencies and allow band gaps to prevent disturbance.
Secondly the hosts need to be smart enough to listen and understand which frequency is currently unused and transmit at a different frequency.
This involves significantly higher processing and takes away the fundamental requirement that a network must be simple.
And as Ron pointed out it wouldnt be Ethernet