10G Auto-negotiation

Working through a circuit turnup, I’d stumbled into a situation where an ISP tech was telling me I needed to enable auto-negotiation on my end of the of the circuit for it to come up, with respect to how they’d provisioned their end.

I was fairly certain the 10GBASE-LR interface we were currently working with didn’t support such a feature set. But I was in the process of questioning myself. I decided to double check against the 802.3-2008 spec that I keep handy in my dropbox folder at all times.

Sure enough, my research proved worthwhile. Contained within the 802.3-2008 Section 4, Clause 44 titled Introduction to 10 Gb/s baseband network, there is a handy diagram to show what features and functionality each flavor of 10G will support from a PHY perspective.

Screen Shot 2013-04-15 at 10.39.16 AM

The interface that I was dealing with was 10GBASE-LR. The ‘L’ meaning long wavelength (1310nm) / Long Reach and ‘R’ meaning scrambled ecoding 64b/66b.

But checking the diagram and finding the 10GBASE-R encoding we can see that there has been no addition of the Auto-negotiation sublayer to that stack. Therefore, auto-negotiation is not supported on 10GBASE-R links.

Checking again, we do see that 10GBASE-T links DO support auto-negotiation. So, any 10G copper interfaces that you turn up, you’ll be able to support it. Otherwise, none of the optical standards have the sublayer incorporated.

Case in point, knowing where to find the information is almost always the largest part of the fight.


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