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HP Auto-MDIX technology

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HP's Auto-MDIX technology describes an apparatus for configuring network media connections in local area networks. Specifically, U.S. Patents 6,175,865 and 6,460,078 describe a means of automatically configuring node interface devices having Media Dependent Interfaces (MDI) to avoid lock step operations and thereby prevent improper connections. The key benefit of this technology is to eliminate the need for special "crossover" cables when connecting LAN devices together.

Description of technology

Many local area network (LAN) products use a medium consisting of twisted pair copper wire pairs for the transmission and reception of data. It is generally a requirement that one or more pairs be used for transmission of data in one direction and one or more other pairs to receive data in the opposite direction. The connection between two node devices is a link. Many LAN devices, which employ a full-duplex medium, have different pairs for transmission than for reception and require, therefore, that each end of the link use a defined assignment for its twisted pair connector to a particular pair of wires. If the transmit pair of wires of one device is connected to the transmit connectors of another, obviously the communication link will fail.

Most LAN standards address this problem by assigning different connector pins to the wires in the twisted pair at the RJ-45, which is often referred to as the Media Dependent Interface (MDI). In switched networks, Network Interface Devices (NIC) may be directly connected to another NIC, or a repeater may be connected to another repeater, or a repeater may alternately be connected to a switch. Depending upon the assignment of pins in the network interface, it is sometimes necessary to use a crossover cable to address the problem that both products use the same pin designations on their interfaces. Determining whether the interface requires this cable can cause confusion and frustration if the customer lacks the necessary cable.

To get around this problem, some products use a manual "MDIX" switch. But that still requires user intervention. The need arose, then, for automatically ensuring viable connections among MDIs in complex LANs. HP's Auto-MDIX technology effectively solves the problem of lock step interaction among devices having MDIs from various well-known manufacturers.


Having licensed the technology to several of the leading PHY device manufacturers, HP is now offering a complete licensing program based around the technology, and the company expects that more than 200 million ports utilizing this technology will ship this year. For further information, contact HP's Intellectual Property Licensing organization.