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Dual Speed Functionality and Switching
The IESH-MB’s 10/100 Mbps RJ45 switch port auto negotiates with the
connected device for the fastest data transmission rate supported by
both devices. The IESH-MB 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
IESH-MB 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 IESH-MB 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, IESH-MB
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 IESH-MB’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 IESH-MB 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 IESH-MB’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.
