Three general classes of failures:
- Bit errors
- 1s turned into 0s or vice versa as packets transmitted over physical link
- Sometimes single bit, but sometimes burst error (several consecutive bits)
- Caused by lightning strikes, power surges, etc.
- Thankfully, pretty rare
- Can be detected and corrected
- Packets lost
- Congested switches - No place left in queue
- Physical link cut or computer crashes