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Multi-Gig AutoNegotiation: Is the cable quality taken into account?
I have a multi-gig PCIe card in my desktop PC now - currently running at 10 gigabits and connected to my XS708Ev2 switch.
I am wondering how the speed would be selected if I had a multi-gig switch. Would it simply take the fastest speed that my PCIe card supports, or would it also take the cable quality (loss/capacitance) into account when it autonegotiates?
Hi StephenB
Thanks for your question. Take it this way: Multi-Gigabit, NBASE-T, IEEE 802.3bz standards are very well done. Auto-negotiation would always happen at the highest speed supported on both sides:
- At your NIC
- at your Switch
But you're right, cable quality would also make part of the equation.
Let me answer your question:
- If your NIC is capable of Multi-Gigabit Ethernet, say 1Gbps, 2.5Gbps and 5Gbps, and if the port on the switch is also capable of Multi-Gigabit Ethernet, the auto-negotiation will end up at the "highest speed" as a common denominator between the two
- If your NIC is connecting to a XS708E today at 10Gbps, it means your NIC is also capable of 10G. It could be a 5-speed NIC card with 100Mbps, 1Gbps, 2.5Gbps, 5Gbps and 10Gbps speeds supported
- Now if the switch also has 5-speed ports with 100Mbps, 1Gbps, 2.5Gbps, 5Gbps and 10Gbps capability, then your NIC should still connect at 10Gbps, provided you're in the 10GBASE-T spec (100-meter on CAT6A wiring; 35- or 45- or 55-meter best case on CAT6, based on cross-talk issues and other interferences)
- If your wiring is not CAT6A, if you have a long run on CAT6, or if you have legacy CAT5E wiring, 10GBASE-T wouldn't happen
- Then, your NIC and the Multi-Gigabit switch would drop to the second highest speed supported - namely 5Gbps
The beauty of 2.5G and 5G new speeds, is that legacy CAT5E / CAT6 wiring full support up to 100-meter.
I hope this helps!
Regards,
2 Replies
Hi StephenB
Thanks for your question. Take it this way: Multi-Gigabit, NBASE-T, IEEE 802.3bz standards are very well done. Auto-negotiation would always happen at the highest speed supported on both sides:
- At your NIC
- at your Switch
But you're right, cable quality would also make part of the equation.
Let me answer your question:
- If your NIC is capable of Multi-Gigabit Ethernet, say 1Gbps, 2.5Gbps and 5Gbps, and if the port on the switch is also capable of Multi-Gigabit Ethernet, the auto-negotiation will end up at the "highest speed" as a common denominator between the two
- If your NIC is connecting to a XS708E today at 10Gbps, it means your NIC is also capable of 10G. It could be a 5-speed NIC card with 100Mbps, 1Gbps, 2.5Gbps, 5Gbps and 10Gbps speeds supported
- Now if the switch also has 5-speed ports with 100Mbps, 1Gbps, 2.5Gbps, 5Gbps and 10Gbps capability, then your NIC should still connect at 10Gbps, provided you're in the 10GBASE-T spec (100-meter on CAT6A wiring; 35- or 45- or 55-meter best case on CAT6, based on cross-talk issues and other interferences)
- If your wiring is not CAT6A, if you have a long run on CAT6, or if you have legacy CAT5E wiring, 10GBASE-T wouldn't happen
- Then, your NIC and the Multi-Gigabit switch would drop to the second highest speed supported - namely 5Gbps
The beauty of 2.5G and 5G new speeds, is that legacy CAT5E / CAT6 wiring full support up to 100-meter.
I hope this helps!
Regards,
Thanks, that's exactly what I wanted to know.
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