ETH100 Rev.
7
5
Switch operation
The ETH100 contains a complete non blocking 3 port Ethernet switch. One port is the fibre
port; the two other ports are the electrical ports. The fibre port is always running in 100
Mbit/s full duplex operation, the two electrical ports can run in 10 or 100Mbit/s, full or half
duplex. The switch incorporates a high performance MAC address lookup engine, which
learns which devices are connected to each port, and minimises traffic on each port.
The switch learns what port an end station is connected to, by remembering each packet
source address (MAC address) and what port the packet came from. Once a MAC address to
port mapping is learnt, all other packets to that MAC address are directed to the correct port
only. If a packet is sent to a new (currently unlearnt) address, the packet will be transmitted
to all ports except the one that the packet came from. This insures the packet will be
received by the correct end station (if it exists), and when the end station responds back, its
address will be learnt by the switch for the next series of packets. The switch will learn up to
4096 MAC addresses. An address mapping will be removed after 10 minutes without packet
traffic from that node.
Important: If you move an end station (e.g. a PC or a router) from one port to
another, you might have to wait for up to 10 minutes before the switch
recognises that the node has moved, and all traffic to that node will be sent to
the wrong port. As soon as the moved end station sends out a packet, the switch
will detect that the node has moved, and the address/port mapping is updated,
and the traffic will continue as before.
network-electronics.com | 8
