I'm selecting PHY IP core for our future chip supporting 10G ethernet.

I have some confusion regarding which 10GBASE-*R standards have auto-negotiation and link training features.

10GBASE-KR, which is for backplane and does not have connector like SPF+ has both features.

Do other standards, like 10GBASE-LR, -MR, -SR or SPF+ Direct Attach (all use SPF+ connector) have that features? If not, do they just send 64/66b encoded bitstream without any link preparations?

  • \$\begingroup\$ Some of this is also core dependent... Just because the protocol supports it does not mean the VHDL does. Altera has burnt me on this before with bus lvds and triple speed Ethernet. \$\endgroup\$
    – MadHatter
    Oct 23, 2015 at 20:11

1 Answer 1


-LR, -SR, and -ER are all just -R. The only difference between -LR, -SR, -ER, and direct attach copper is the medium in between the SFP+ modules. Direct attach copper is just a copper wire, -SR is multi-mode fiber with 850 nm VCSELs, -LR is single mode fiber with 1310 nm lasers, -ER is single mode fiber with 1550 nm lasers. All of these send raw 64b/66b encoded data without link auto-negotiation or link training.

-KR is special in that it has extra auto-negotiation features.

Source: IEEE 802.3-2008, section 4.

  • \$\begingroup\$ So then, a good 10GBASE-KR phy with auto-neg and training disabled could be used as well for all other SFP+-based standards in a family? \$\endgroup\$
    – lvd
    Oct 26, 2015 at 12:00
  • \$\begingroup\$ How do you know if the "link is up" on 10GBASE-R? CDR PLL locked? \$\endgroup\$
    – pc3e
    Jan 13, 2016 at 14:15
  • \$\begingroup\$ Yeah, CDR locked plus 64b66b frame sync. \$\endgroup\$ Jan 13, 2016 at 17:42

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