Appendix B: Auto Negotiation
10/100/1000Mbps Copper Ethernet Auto Negotiation
202 SmartBits System Reference
Auto Negotiation Enabled
SmartBits test applications can be run with auto negotiation enabled or disabled.
When auto negotiation is enabled for a port, SmartBits advertises the speed and duplex
settings that have been set (either using the GUI interface or through SmartLib
commands), using the standard auto negotiation protocol.
Because the test goal is to verify the capabilities of the device under test (DUT), not of
SmartBits, the normal test methodology is to let SmartBits advertise speed and duplex
options one at a time, then observe the ability of the device under test (DUT) to respond.
This is done by setting the MII registers to enable auto negotiation and to advertise a
specific speed and duplex capability rather than multiple speed/duplex capabilities.
A test begins with the link initialization and verification steps. It is during this stage that
the auto negotiation process occurs (if selected). Then the test runs to completion, using
the selected settings. SmartBits will not change a port’s configuration during the
execution of a test iteration. However, different capabilities can be advertised and
negotiated by modifying the MII registers, then restarting the test.
Spirent Communications test applications such as SmartApplications, AST II,
SmartFlow, and SmartMulticastIP also offer the following three configuration options for
auto negotiation:
• Disable AN (commonly used).
• Force AN (commonly used).
• Registers Untouched (for custom advanced test applications).
The first two of these (Disable AN and Force AN) are used in most normal test situations.
The third (Registers Untouched) is designed to be used only in special test situations. All
three options are described in more detail below.
Auto Negotiation Disabled
SmartBits test applications can be run with auto negotiation enabled or disabled.
In applications such as SmartApplications, AST II, SmartFlow, and SmartMulticastIP, the
Disable AN option sets the appropriate MII registers to the user-selected flow control,
speed, and duplex settings. It sets Register 0 to disable auto negotiation on the port. With
this option, the SmartBits port does not participate in the auto negotiation protocol;
however, it does advertise the speed/duplex combination that has been set in the
advertisement register.
With this option, it is important to verify that both the SmartBits port and the DUT port
are configured to have the same values for flow control, speed, and duplex. Because AN
is disabled, a mismatch will not be resolved through the AN negotiation process.
Note: When Disable AN or Registers Untouched (see below) are selected, the
application cannot verify that the duplex settings are correct, because the link verification
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