History: Switches

￿Switch = Multiport Bridges with HW acceleration

￿Full duplex ￿ Collision-free Ethernet ￿ No CSMA/CD necessary anymore

￿Different data rates at the same time supported

￿Autonegotiation

￿VLAN splits LAN into several broadcast domains

1000 Mbit/s

100 Mbit/s

100 Mbit/s

Collision-free

plug & play

scalable Ethernet !

10 Mbit/s

(C) Herbert Haas 2005/03/11

6

 

 

Several vendors built advanced bridges, which are partly or fully implemented in hardware. The introduced latency could be dramatically lowered and furthermore other features were introduced, for example full duplex communication on twisted pair cables, different frame rates on different ports, special forwarding techniques (e,g, cut through or fragment free), Content Addressable Memory (CAM) tables, and much more. Of course marketing rules demand for another designation for this machine: the switch was born.

Suddenly, a collision free plug and play Ethernet was available. Simply use twisted pair cabling only and enable autonegotiation to automatically determine the line speed on each port (of course manual configurations would also do). This way, switched Ethernet become very scalable.

Furthermore, Virtual LANs (VLANs) were invented to split the LAN into several broadcast domains. VLANs improve security, utilization, and allows for logical borders between workgroups.

6