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Altera_Forum
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13 years ago

Ethernet autonegotiation

I am just wondering what kind of procedures are running during the link establishment in 100Base-T ethernet in case auto negotiation is disabled (i.e. forced mode) at both ends of the ethernet con...
Altera_Forum's avatar
Altera_Forum
Icon for Honored Contributor rankHonored Contributor
13 years ago

FLPs are not transmitted if aneg is disabled, just idle. If a device that supports aneg sees idle from a link partner (instead of FLPs), then it can link with it via a "parallel detection" function. The device will assume the link is half duplex, since it doesn't know if the link partner is a half or full duplex device. It's typically a bad situation, since you can get a duplex mismatch. See Clause 28 of the IEEE 802.3 standard for a reference (28.2.3.1 in particular for a description of Parallel Detection).