link_layer

Link Layer (or Physical Layer)

Deals with the problems connecting one computer to another computer.

• Only worries about data across one hop.
• Like what voltages to use,
• How to send data.
• How to deal with multiple computers using the same wire.

The tech that came out of this are

• Ethernet
• WiFi
• Cable Modem
• DSL
• Satellite
• Optical

Link Layer Addresses

All link devices like Wireless Modules have a specific address built into them by the manufacturer. MAC Address

Q: How do we ensure that, in an environment where multiple devices are hooked to something like an Ethernet Hub or like a WiFi Network, if two devices want to talk to each other, they can so.

A: The address of the sender and receiver is encoded into the packet

Avoiding Chaos

For Ethernet, it uses Carrier Sense Media Access with Collision Detection (CSMA/CD):

0. We have a data ready to go
1. "Listen". If there is already data being transferred, wait.
2. Once it goes silent, send.
3. Listen again to see if your own data is coming back. If so, great.
4. If a collision does happen, the data needs to back off. "Complex math (Private)" makes it so that fairness is maintained.

• technology
• application_layer