We will look at how Wi-Fi handles this in its most common mode of operation in 4.2.1 Wi-Fi and Collisions. If A and B now transmit simultaneously, C will encounter a collision, but there is no way for A or B to detect this collision directly.Īs a result, wireless protocols must be constructed appropriately.
Even if signal strength could be resolved, there is also the “hidden-node problem”, in the following section and also at 4.2.1.4 Hidden-Node Problem): perhaps nodes A and B can both communicate directly with C, but there is a radio-opaque wall blocking any direct communication between A and B. However, with radio the remote signal might easily be as little as 1/1,000,000 of the transmitted signal (-60 dB), as measured at the transmitting station, and it is simply overwhelmed during transmission. Along a wire-based Ethernet the remote signal might be as weak as 1/100 of the transmitted signal but that 1% received signal is still detectable during transmission. To some extent, this has to do with the relative signal strength of the remote signal at the local transmitter. 4.2.1.2 Collision Avoidance and BackoffĮthernet-like collision detection is no longer feasible over radio.
0 kommentar(er)
