May 2011
Intermediate to advanced
788 pages
23h 34m
English
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How Autonegotiation Works
First, let’s cover what autonegotiation does not do: when autonegotiation is enabled on a port, it does not automatically determine the configuration of the port on the other side of the Ethernet cable and then match it. This is a common misconception that often leads to problems.
Autonegotiation is a protocol and, as with any protocol, it only works if it’s running on both sides of the link. In other words, if one side of a link is running autonegotiation and the other side of the link is not, autonegotiation cannot determine the speed and duplex configuration of the other side. If autonegotiation is running on the other side of the link, the two devices decide together on the best speed and duplex mode. Each interface advertises the speeds and duplex modes at which it can operate, and the best match is selected (higher speeds and full duplex are preferred).
The confusion exists primarily because autonegotiation always seems to work. This is because of a feature called parallel detection, which kicks in when the autonegotiation process fails to find autonegotiation running on the other end of the link. Parallel detection works by sending the signal being received to the local 10Base-T, 100Base-TX, and 100Base-T4 drivers. If any one of these drivers detects the signal, the interface is set to that speed.
Parallel detection determines only the link speed, not the supported duplex modes. This is an important consideration because the common modes of Ethernet ...
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O’Reilly covers everything we've got, with content to help us build a world-class technology community, upgrade the capabilities and competencies of our teams, and improve overall team performance as well as their engagement.Julian F.
I wanted to learn C and C++, but it didn't click for me until I picked up an O'Reilly book. When I went on the O’Reilly platform, I was astonished to find all the books there, plus live events and sandboxes so you could play around with the technology.Addison B.
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I'm always learning. So when I got on to O'Reilly, I was like a kid in a candy store. There are playlists. There are answers. There's on-demand training. It's worth its weight in gold, in terms of what it allows me to do.