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Dual Speed Functionality and Switching
The EDS’s 10/100 Mbps RJ45 switch port auto negotiates with the
connected device for the fastest data transmission rate supported by both
devices. The EDS is a plug-and-play device, so software configuration is
not required at installation or during maintenance.
The half/full duplex mode for the RJ45 switched ports is user dependent
and changes (by auto-negotiation) to full or half duplex, depending on
which transmission speed is supported by the attached device.
Switching, Filtering, and Forwarding
Each time a packet arrives at one of the switched ports, a decision is
made to either 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 a 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 EDS
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.
Switching and Address Learning
The Moxa EDS has an address table that can hold up to 8,000 node
addresses, which makes it suitable for use with large networks. The
address tables are self-learning, so that as nodes are added or removed,
or moved from one segment to another, EDS automatically keeps up with
new node locations. An address-aging algorithm causes the least-used
addresses to be deleted in favor of newer, more frequently used
addresses. To reset the address buffer, power down the unit and then
power it back up.
Auto-Negotiation and Speed Sensing
The EDS’s RJ45 Ethernet ports independently support auto-negotiation
for transmission speeds of 10 Mbps or 100 Mbps, with operation
according to the IEEE802.3 standard. This means that some nodes could
be operating at 10 Mbps, while at the same time, other nodes are
operating at 100 Mbps.
When an RJ45 cable is connected, auto-negotiation takes place, and then
each time a LINK is enabled. The EDS advertises its capability for using 10
Mbps or 100 Mbps, transmission speeds, with the device at the other end
of the cable expected to advertise similarly. Depending on what type of
device is connected, this will result in agreement to operate at a speed of
10 Mbps or 100 Mbps.
If an EDS’s RJ45 Ethernet port is connected to a non-negotiating device,
it will default to 10 Mbps speed and half-duplex mode, as required by the
IEEE802.3 standard.
