Auto-Negotiation

The auto-negotiation protocol, as specified by the 100BASE-T standard, selects the operation mode (half-duplex or full-duplex) at boot time or when the link state changes (the link goes down or tried to come up). The auto-negotiation protocol also selects the speed and the full duplex or half duplex mode.

The auto-negotiation protocol does the following:

• Identifies all link partner-supported modes of operation

• Advertises its capabilities to the link partner

• Selects the highest common denominator mode of operation based on the following priorities:

  • 100 BASE-T4

  • 100 Mbps, full-duplex

  • 100 Mbps, half-duplex

  • 10 Mbps, full-duplex

  • 10 Mbps, half-duplex

The link partner is the networking device (system, Ethernet hub, or Ethernet switch) at the other end of the link or cable. If the SUNW,hme device is connected to a remote system or interface that is not capable of auto-negotiation, the system automatically selects the correct speed and half-duplex mode.

If adapters or systems are connected to a link partner and the auto-negotiation protocol fails to operate successfully, you can configure the device so it does not use this protocol. This forces the driver to set up the link in the mode and speed that you choose instead of using the auto-negotiation protocol.

Internal Transceiver

The internal transceiver is a feature supported by the driver and is capable of all the operating speeds and modes (except the 100BASE-T4 mode) listed in the section "Operating Speeds and Modes"," earlier in this chapter. When the internal transceiver is used, the default is auto-negotation by the hme driver, which automatically selects the speed and mode of the link. The internal transceiver performs auto-negotiation with the remote end of the link (link partner) to select a common mode of operation.

The internal transceiver also supports a forced mode of operation. This is where the user selects the speed and mode using the ndd utility, the /etc/system file, or the hme.conf file. The ndd utility makes calls to the hme driver to choose the speed and mode.

External Transceiver

When an external transceiver (not present on the SunSwift SBus Adapter) is connected to the MII interface, the driver selects the external transceiver for networking operations.

• If the external transceiver supports auto-negotiation, the driver uses the auto-negotiation feature to select the link speed and mode.

• If the external transceiver does not support auto-negotiation, the driver selects the highest priority mode supported by the transceiver.

You can also manually select the speed and mode of the link. For example, two transceivers might not support the same mode and speed. Therefore, you must select the highest mode and speed that both transceivers support using the ndd utility. See the list of operating speeds and modes in the section, "Operating Speeds and Modes"," in this chapter.