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Duplex negotiate

IP.com Disclosure Number: IPCOM000020461D
Original Publication Date: 2003-Nov-21
Included in the Prior Art Database: 2003-Nov-21
Document File: 1 page(s) / 34K

Publishing Venue

IBM

Abstract

This publication covers duplex negotiation whereby the number of collision on the network per second is examined and the connection is negotiated properly to prevent performance degradation of the network link. If the link level protocol was determined through auto-negotiate, and selected half duplex, the connection would be upgraded to full duplex if a threshold number of collisions per second is seen on the network.

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Duplex negotiate

Auto-Negotiation is a mechanism that takes control of the cable when a connection is established to a network device. Auto-Negotiation detects the various modes that exist in the device on the other end of the wire, the Link Partner, and advertises it own abilities to automatically configure the highest performance mode of inter-operation..

In theory, if Auto-Negotiation exists at only one end of a twisted-pair link, it determines that the Link Partner does not support the Auto-Negotiation mechanism. Instead of exchanging configuration information, it examines the signal it is receiving. If Auto-Negotiation discovers that the signal matches a technology that the device supports, it will automatically connect that technology. This function, known as Parallel Detection. In the event that no common technology exists, Auto-Negotiation will not make a connection. This ensures preservation of network integrity and minimization of network down time (again in theory).

In practice, it is known in a number of actual cases where auto-negotiation has incorrectly configured the network, thereby substantially degrading the network. In all cases where this has been seen it's be due to one or more hosts having a fixed link speed and full duplex. This problem is not localized to any particular company, and shows up in an internet search as being a problem for other operating systems and hardware vendors. This problem has been reproduced on a variety of operating...