Transmission of raw bits over a communication link
Repeaters
- Used for solving distance limitation in LANs
- Electrical signal becomes weaker as it travels, imposing limit on length of LAN
- Repeaters join LANs together
- Analog electrical device
- Continuously monitors electrical signals
- Transmits an amplified copy
Hubs
- Joins multiple input lines electrically
- Designed to hold multiple line cards
- Unlike repeater, does not (necessarily) amplify signal
- Unlike repeater, hub is not analog and does not just repeat the signal
- Regenerates signal, so noise gets removed
Limitations of Repeaters and Hubs
- One large shared link
- Each bit is sent everywhere
- So aggregate throughput is limited
- Cannot support multiple LAN technologies
- Does not buffer or interpret frames
- Can’t interconnect between different rates/formats
- Limitations on maximum nodes and distances
- Shared medium imposes length limits
- e.g. can’t go beyond 2500 meters on Ethernet