|  | 4.3 | Basics of Signals and Noise in Communications Systems
| 4.3.6 | Network reflection
To understand reflection, imagine having a slinky or a jump rope stretched out with a friend holding the other end. Now, imagine sending them a pulse or a 1 bit message. If you watch carefully, you will see that a small wave (pulse) returns (reflects) to you. Reflection occurs in electrical signals. When voltage pulses, or bits, hit a discontinuity some energy can be reflected. If not carefully controlled, this energy can interfere with later bits. Remember, while you are focused on only 1 bit at a time right now, in real networks you will want to send millions and billions of bits every second, thus requiring you to keep track of this reflected pulse energy. Depending on the cabling and connections that the network uses, reflections may or may not be a problem. Reflection also occurs with optical signals. Optical signals reflect whenever they hit a discontinuity in the glass fiber, such as when a connector is plugged into a device. You can see this effect at night if you look out a window. You can see your reflection in the window even though the window is not a mirror. Some of the light that is reflected off your body reflects in the window. This also happens with radio waves and microwaves as they encounter different layers in the atmosphere. This may cause problems on your network. For optimal network performance, it is important that the network media have a specific impedance in order to match the electrical components in the NICs. Unless the network media have the correct impedance, the signal will suffer some reflection and interference will be created. Then multiple reflecting pulses can occur. Whether the system is electrical, optical, or wireless, impedance mismatches cause reflections. If enough energy is reflected, the binary, two-state system can become confused by all the extra energy bouncing around. You can resolve this by ensuring that all networking components are carefully impedance matched.