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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 NI UES-3880 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 NI UES-3880 has an address table that can hold up to 1K 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, the NI UES-3880 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 NI UES-3880 is a RJ45 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 RJ45 cable connection is made, and then
each time a LINK is enabled. The NI UES-3880 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 similarly advertise. 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.
If the NI UES-3880 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 IEEE 802.3u standard.