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1 Introduction
8
Hot Plug NIC Installation
If your computer supports PCI hot plug specifications, you can add a new 3Com NIC or
remove and replace a 3Com NIC without turning off power to the computer. Hot plug
NIC installation allows you to expand connections without taking the computer out of
service. It makes troubleshooting faster and easier because you do not need to wait for
the computer to reboot.
For instructions on performing a hot plug NIC installation, refer to your computer
documentation.
Flow Control Features
The 3C990B NICs use flow control technology to throttle the incoming data packet stream
and prevent the loss of packets. IEEE 803.2x flow control prevents the input buffers of a
device from overflowing. By using pause frames to communicate buffer status between
linked transmitting and receiving devices (transmitters and receivers). A receiver sends a
pause frame to tell a transmitter to stop the transmission of data frames for a specified
period, allowing the receiver’s input port buffers to empty before receiving new packets.
Pause Frames
When a transmitter receives pause frames, it suspends transmission for the specified
period. When the receiver’s input buffers can store packets again, it can either send
another pause frame to tell the transmitter to resume transmission, or wait for
transmission to resume at the end of the specified period.
With asymmetric flow control, only one of two linked devices can receive pause frames.
With symmetric flow control, both linked devices can send and receive pause frames.
Link Negotiation
Related to flow control is the auto negotiation capability, in which linked devices advertise
their flow control capabilities and automatically select the best common mode of
communication.
Rare cases (for example, linking to a device that does not support auto-negotiation) may
require that auto-negotiation be disabled on a port, thereby enabling forced link on that
port. When forced link is enabled, linked devices must have matching flow control
capabilities. For example, a port that is set for forced link and reception flow control can
connect successfully only with a port that is set for forced link and transmission flow control.
Offline Diagnostics
The NIC software includes offline diagnostics programs for configuring, testing, and
troubleshooting NICs. The configuration program within the DOS diagnostics program is used
for a PC running DOS or NetWare. The 3Com NIC diagnostics program (3Com NIC Doctor) is a
Windows-based program used for a PC running Windows 2000, Windows NT 4.0, Windows
Millennium Edition (Windows Me), Windows 98, or Windows 95.