10
Switching, Filtering, and Forwarding
Each time a packet arrives at one of the switched ports, a decision is
made to filter or forward the packet. Packets with source and
destination addresses belonging to the same port segment will be
filtered, constraining those packets to one port, and relieving the rest of
the network from the need to process them. A packet with destination
address on another port segment will be forwarded to the appropriate
port, and will not be sent to the other ports where it is not needed.
Packets that are used in maintaining the operation of the network (such
as the occasional multi-cast packet) are forwarded to all ports. The IE-
SW-IP67(T)-5M12 operates in the store-and-forward switching mode,
which eliminates bad packets and enables peak performance to be
achieved when there is heavy traffic on the network.
Auto-Negotiation and Speed Sensing
All of the IE-SW-IP67(T)-5M12
’s Ethernet ports independently support
auto-negotiation for speeds in the 10BaseT and 100BaseTX modes,
with operation according to the IEEE 802.3u standard. This means that
some nodes could be operating at 10 Mbps, while at the same time,
other nodes are operating at 100 Mbps.
Auto-negotiation takes place when an M12 cable connection is made,
and then each time a LINK is enabled. The Switch advertises its
capability for using either 10 Mbps or 100 Mbps transmission speeds,
with the device at the other end of the cable expected to advertise in the
same way. Depending on what type of device is connected, this will
result in agreement to operate at a speed of either 10 Mbps or 100
Mbps.
Note about possible lost of data packages in case of
“Duplex
mismatching”
If the Switch
’ AutoNeg-Port is connected to a
non-negotiating
device,
then the Switch will set its port transmission speed same as the
connected device but is unable to correctly detect the duplex mode. As
result the port is set to the correct speed but is using always the half
duplex mode as required by the IEEE 802.3u standard in such cases.
For correct transmission the non-negotiating port has to be set to half-
duplex mode (speed either 10 or 100 Mbit/s).
