What is a Transmission Medium?
In The Five Components you met the communication media: the path a message travels along. This chapter is about those paths — the cables and the waves that actually carry every message you send.
1What a transmission medium is
You use transmission media all the time without the name. When you switch on a fan, the electric wire is the medium that carries current from the switch to the fan. When two people talk, the medium is the air.
2Two kinds: wired and wireless
A physical link — a wire or cable — carries the signal from node to node. The signal is guided: it can only go where the cable goes.
- Twisted pair cable — electric signals
- Co-axial cable — electric signals
- Fibre-optic cable — light
The data travels through the air as electromagnetic waves, sent and received by antennas. Nothing guides it along a path.
- Radio waves
- Microwaves
- Infrared waves
Twisted pair and co-axial cable carry electric signals through copper. Fibre-optic cable carries light through glass. Here are all six, joining the same two buildings.
Pick a medium and watch how the signal gets from Block A to Block B. Drag sideways to turn.
Not to scale. In the infrared view the two blocks are much too far apart for infrared, which is the point.
Each medium has its strengths. The lessons that follow take them one at a time, and the two compared pages show how to choose between them in a case study.
3Check yourself
Which of these is a guided (wired) transmission medium?
What does a fibre-optic cable carry, unlike twisted pair and co-axial cable?