# Clock Drift

Recalibrate clocks when out of sync:

- Async Transmission
	- Send a small amount of data, then 1, then 0, then some more data.
- Manchester Encoding
	- Send each bit as 2 values
	- Original 10MBase-T uses this
- HDB3 encoding
	- 3 logic levels to ensure no static sequences
	- Used for long distance cables
- 4B5B encoding
	- Transmit 5 bits of signalling to represent 4 bits of data
	- 100MBase-T uses this.

# Quantities in Digital Communication

## Bit

- Short for "binary digit". Byte = 8 bits

## Data Rate

- Bits per second

## Baud Rate

- Times per second the transmitted signal changes.

### Examples

- A modem used for dialup will encode at least six bits of data for each unit of signalling.
- Ethernet uses between 1.2 and 2 units of signalling per bit of data.

# Text Encoding Communication

- The word "Up" -> ASCII is 85, 112
- Binary stream -> 010101010110000
This demonstrates the worst case scenario for 4B5B, and 4 zeros to demonstrate HDB3.