Switched Ethernet

Switched Ethernet is an evolution of classic Ethernet that replaces shared hub-based networks with intelligent switches. First standardized in the 1980s as IEEE 802.3, Ethernet technology is classified into two main categories: classic Ethernet and switched Ethernet.

In switched Ethernet, the hub that connects stations in classic Ethernet is replaced by a switch. The switch connects a high-speed backplane bus to all stations in the LAN through dedicated connections. A typical switch contains 4 to 48 ports, allowing stations to connect simply by plugging into any available port. Connections can extend to computers, peripherals, other Ethernet switches, or hubs.

Working Principle

Unlike classic Ethernet where the channel is shared among all stations, switched Ethernet provides each station with a dedicated connection. When a switch port receives a frame, it examines the destination address and forwards the frame only to the appropriate outgoing port.

This dedicated connection architecture eliminates collisions in the channel. However, collisions may still occur at a destination port if it receives frames from multiple source ports simultaneously. Each port maintains its own collision domain and resolves conflicts independently.

Frame Format

Switched Ethernet uses the same frame format as classic Ethernet, consisting of the following fields:

• Preamble − 8 bytes providing synchronization and timing information

• Destination Address − 6 bytes containing the physical address of the receiving station

• Source Address − 6 bytes containing the physical address of the sending station

• Length − 2 bytes indicating the number of bytes in the data field

• Data − Variable-sized field carrying upper layer data (maximum 1500 bytes)

• Padding − Extra bits ensuring minimum frame size of 46 bytes

• CRC − 4 bytes for error detection

Advantages of Switched Ethernet

• Elimination of collisions − Dedicated connections prevent channel collisions

• Full-duplex communication − Simultaneous sending and receiving on each port

• Bandwidth efficiency − Each port gets full bandwidth allocation

• Scalability − Easy addition of new stations through available ports

Conclusion

Switched Ethernet revolutionizes traditional Ethernet by replacing shared hubs with intelligent switches that provide dedicated connections to each station. This architecture eliminates collisions, improves bandwidth utilization, and enables full-duplex communication while maintaining compatibility with the original Ethernet frame format.