Operating at the Highest Performance Mode

If the 10BASE-T hub in the previous example is later replaced with a 100BASE-T repeater hub, then the dual-speed interface will receive FLPs when the hub is turned on, and the Auto-Negotiation protocol will result in the interface and hub port both operating at 100-Mbps as long as all interfaces connected to the repeater hub can operate at 100-Mbps. The switch from 10-Mbps to 100-Mbps will occur with no manual intervention.

Auto-Negotiation ensures that all devices attached to the hub are operating at the highest common denominator. Since a repeater hub is used to create a shared signal channel for all devices attached to the repeater ports, that shared signal channel must operate no faster than the slowest device attached to it.

If an Auto-Negotiation repeater hub has one of its ports attached to a device that only supports 10BASE-T, with the rest of the ports attached to 100BASE-T devices, then the hub will negotiate a speed of 10-Mbps for all ports, since that is the highest common denominator for all repeated ports. When every device attached to the repeater hub is capable of operating at 100-Mbps, then the hub will negotiate 100-Mbps for all ports.

If there is no common technology detected at either end of the link, then the Auto-Negotiation protocol will not make a connection, and the port will be left in the off condition. For example, if a 100BASE-T4 device is connected to a port on a 100BASE-TX switch, no connection will be established on that link.

Quick Reference Guide to Auto-Negotiation - 09 SEP 95

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