Unit 4 Summary

Make a circuit between the nodes, and send two different electrical signals different voltages, frequencies, to mean 0 or 1. The basics of how electricity can be graphed and how those graphs show features that can be changed by the sender and sensed by the receiver, so that nodes can use those features to encode data. Besides the fundamental ideas of how to use electricity to send data, some standards require two circuits, with one for each direction. It also discusses how circuits can actually interfere with each other, and what might be done to reduce the effects of this electromagnetic interference
(EMI), including the use of twisted-pair cabling. Ethernet LANs use copper UTP cabling, RJ-45 connectors, and all the specifics needed to make an actual Ethernet link work. Fiber optics use light to transmit data, often using an encoding with the light off meaning 0 and the light on meaning 1. These cables allow longer distances compared to copper, with no EMI, so network engineers use them for longer links. In LANs, these links often connect switches in different buildings; in WANs, they connect different sites inside the Telco or ISP network. Wireless technologies that use radio to send bits. These links include the wireless technology many of us use every day with our mobile phones. These phones connect to mobile networks, which connect the phones to the rest of the world’s networks, both for voice and data. The radio part of the picture requires the phone and radio tower to encode data radio waves, often with encoding that uses amplitude or phase shifts.
To send data over a link using electricity, nodes vary the electrical signal sent over a link over time. An electrical circuit must first exist as a complete loop of material over which electricity can flow, with copper wire, you cannot create an electrical flow over one wire with its ends connected to nothing. If you put it into a complete loop, electricity can flow.