this is the hidden terminal problem:
- A opens a transmission to B.
- A cannot transmit to C, since C is out of A's range.
- C starts a transmission to B, and because it can't sense the current transmission between A & B (because A is too far away), there will be data collision at B.
But why can't C detect (carrier sense) the data flow in the outer bounds of its range?? there is clearly an intersection of both A's and C's ranges, so carrier sense should detect something's going on...
and does it in turn mean that a transmission like this would be impossible, just because the actual device is not in direct range?
i don't get what you're saying. of course it wouldn't send right away because of this exact problem, which is why there are things like busy tones or RTS/CTS.
the hidden terminal problem states this:
there is an ongoing transmission between A & B. C is too far away from A to be able to sense there's a transmission going on. So C deducts the channel is free and starts sending to B, leading to data collision at B.
i just don't understand why C is unable to detect the transmission between A&B, because the ranges clearly intersect...
anon (>>7855189) said sensing would already interfere and i wonder why, because in turn that would mean that A should actually be to detect C _because_ of that intersection of ranges
or is maybe this here the correct illustration for the hidden terminal problem?
this would explain better why A can't see C and why C would transmit to B even if there was an ongoing transmission between A & B already
>i just don't understand why C is unable to detect the transmission between A&B, because the ranges clearly intersect...
just because your signal intersects with someone elses doesn't mean you can listen to it.
A is just too far from C for it to ever reach it.
>just because your signal intersects with someone elses doesn't mean you can listen to it
is this really the case? of course there are going to be strong fluctuations of signal strength and distortion close to the outer border of the range - i would just expect the fluctuations to sometimes fall in such a way that carrier sense would indeed find something - hence the other illustration at >>7855354 that would makes this clearer.
but if the way you state is really the case, then we have a simple answer and i'll be satisfied.
Drop rocks into a lake of water at those points in the picture.
Rock A will have waves that will never reach C but will interfere with B somewhat.
Those interference's will reach C but they will be so small that you won't be able to detect them.
coming back again...
so, first picture at OP:
>Rock A will have waves that will never reach C but will interfere with B somewhat
ok. this means, B is able to pick up A's weak signal.
at the same time, this should mean that C is able to pick up the same weak signal since C's range goes as far as B.
or does this simply mean: B has full energy to pick up signal at this point and therefore manages to read the weak signal, while C's pick-up-signal is too weak already at point B?