|  | 4.3 | Basics of Signals and Noise in Communications Systems
| 4.3.10 | Messages in terms of bits
After a bit reaches a medium, it propagates, and may experience attenuation, reflection, noise, dispersion, or collision. You want to transmit far more than 1 bit. In fact, you want to transmit billions of bits in one second. All of the effects, so far described, that can occur to 1 bit, apply to the various protocol data units (PDUs) of the OSI model. Eight bits equal 1 byte. Multiple bytes equal 1 frame. Frames contain packets. Packets carry the message you wish to communicate. Networking professionals often talk about attenuated, reflected, noisy, dispersed, and collided frames and packets.