Media has a specific connotation in networking. Media refers to the actual substance that carries the network activity. There are many types of media – coaxial cable, twisted-pair (CAT5 ethernet cable and its many successors), and fiber are common examples of physical network media. These are used to physically connect computers and network equipment together and remain the most performant and stable, but have a significant limitation in that the setup requires dragging a cable of some type around, ensuring there are enough places to plug in, and possibly putting the cable inside walls. Servers tend to be plugged in, but most mobile workstations tend not to be since plugging and unplugging network cables is inconvenient.
This will be a series!
Check back at this page as I will be adding more articles over time.
- What Is A Network?
- Computer Roles In A Network
- Network Services
- The OSI model
- Layer 1 (media)
- Layer 2 (Link Layer) Part One
-
* denotes layers of chief importance to programmers
Recall the following from the “Introduction to Networks” post:
Network Equipment
- Modem
- A modem (modulator, demodulator) translates signals between media. In this case, the signal is being translated between the long-range cable or fiber to your residence, and the short-range cable or WiFi inside your residence
A modem is actually a nearly pure Layer 1 piece of equipment. The primary responsibility of technology at Layer 1 is to connect two endpoints for communication, and this is actually a complicated task. Signal has to be detected (on vs off); which requires detecting the presence of light on fiber, electrical current on copper, or radio signals. That means that signal has to be separated from noise and interference. Additionally, the two ends have to agree on how long each individual signal lasts. At this layer, everything is being transmitted in terms of off (0) or on (1), and what if you have a signal that looks like 1, 0, 1, 0, … 1, 1, 0, 0 ? When it comes to these repeated signals, both sides need to agree on how long a 1 or a 0 is transmitted to be counted as a single bit of transmission or more bits (1s or 0s). This process is called synchronization and it is the process by which anything with a physical or radio connection agree on their timing and clock speeds.
Security
While there can be some security implemented at this level, that tends to be expressed as physical access controls. Examples of Layer 1 security risks are “Vampire Taps” which are tools used to splice into physical cables and observe the traffic, and radio traffic observers which are tools used to capture radio signals and interpret them as data. Protecting the security of a network on layer 1 is the responsibility of the organizations who manufacture, own, and maintain networking equipment.
Physical Connections vs Wireless Connections
BlueTooth and WiFi are both non physical network media that communicate by transmitting radio waves through the air. These can be more convenient than plugging in cables, but crosstalk, network congestion, and interference from obstructions make this media less stable than physical media. Additionally, physical media still has higher bandwidth than WiFi.
Balancing between performance requirements and different use cases is part of network architecting, and leaving room for different secure network access methods depending on different use cases is a core responsibility of network design.
Common Issues at Layer 1 that may affect a developer
Layer 1 is sometimes informally referred to as the “lights on” stage. Since this layer is concerned primarily with connecting a circuit or sensing the presence of an access point, issues with this layer have historically been able to be identified by status LEDs failing to light when the appropriate media is connected. A Layer 1 issue is rarely a developer’s direct responsibility to solve.
Layer 1 issues are rarer, but typically fall into a few camps:
- Cable has been unplugged or cut (telecoms admins like to joke that if you bury a cable when lost in the woods, someone with a backhoe will be by to cut the cable and rescue you promptly)
- Interference
- Too many competing signals on the same channel (WiFi)
- Too many competing signals saturating the media (WiFi, copper)
- Improper or under-specced shielding on copper media like coax or ethernet cable
Connections to other layers
A combination Layer 1 and Layer 2 issue is the network loop. This is usually caused by something like plugging the same cable into two ports on a switch, and is also caused by improper configuration when two switches are connected by multiple cables. It makes the switch angry because having multiple paths to the other switch means that they keep shouting at each other. This drowns out the normal traffic.
Thank you for reading. Please let me know if there are any clarifications I can make or further questions I can answer either down in the comments, on LinkedIn, or hit me up on Mastodon.