Hi,
Here some theory:
Auto Negotiation vs. Auto Detection
A Technical Brief
While the IEEE 802.3 working group developed the 100BASE-T standard, several proposals for a scheme by which nodes could automatically configure themselves on a network were introduced. The proposal with the widest support was later integrated into the 100BASE-T standard under the name Auto Negotiation (which was also known as "NWay" before it became a formal specification within the IEEE standard). This brief introduces Auto Negotiation and compares it to other solutions some vendors provide today.
Auto Negotiation
Auto Negotiation is an integral but optional component of the 100BASE-T Fast Ethernet standard. It is a signaling scheme similar in concept to that used by modems, by which network devices advertise their abilities to adjacent nodes. When a connection is established between two devices with Auto Negotiation, the nodes send signals that indicate their operational capabilities, detect the adjacent nodes capabilities, and automatically configure themselves to operate at the highest performance mode common to them.
Auto Negotiation:
Determines the operational speed of connected network devices (10 Mbps or 100 Mbps) and configures accordingly to operate at the highest common speed Does not require installing, adding, or changing drivers because it uses functionality built into the electronic circuitry of the network devices and is not a software driven mechanism Supports 10BASE-T, 100BASE-T, 100BASE-TX, 100BASE-T4, and Full Duplex modes Supports legacy 10/100BASE-T, which means devices with and without Auto Negotiation are fully compatible and interoperable Provides graceful rejection, a feature that protects the network against connections the hub cannot recognize or accept Provides a management interface to the physical layer silicon Supports future 100BASE-T standards, such as 100BASE-T2
Auto Detection
Auto detection, also known as auto sensing or speed sensing, is a function some vendors currently ship with their products. It determines the operational speed of connected network devices (10 Mbps or 100 Mbps) and selects the same operational mode for itself. In this way, the technology is similar to Auto Negotiation, which also supports speed sensing as one aspect of its functionality. That is where the similarity ends.
Auto detection is only a speed sensing mechanism; it does not support the additional features Auto Negotiation provides. It is not a standardized technology, but an assortment of proprietary ones developed by various vendors. It was designed as a short term solution to match adapter speed to network speed while Auto Negotiation technology was being designed into next generation 100BASE-T products. Auto detection does not comply with the 100BASE-T standard. Auto detection is executed with drivers at the software level rather than at the physical level, as with Auto Negotiation. As a result, there are timing and execution issues related to auto detection that may be challenging in terms of interoperability with fully standardized 100BASE-T Auto Negotiation. Early independent tests show compatibility issues may arise when connecting devices with auto detection and those with Auto Negotiation.
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