Copper cabling is the lowest cost, lowest latency, and lowest power way to interconnect high-speed systems together. DAC cables “directly attach” the electrical subsystems together, hence the name Direct Attach Copper cables (DACs). DAC copper cables are mainly used for inside system racks linking compute servers to storage subsystems within the 3-meter maximum length.
Offered in twin-port OSFP, OSFP, and QSFP112 ends
DACs offer length of 0.5m to 2-meters for straight cables, and up to 3-meters for splitters
Power consumption is 0.1 Watts per end
Thin 30AWG wire is used for short lengths up to 1-meter for 800G-to-800G cables
Thicker 26AWG wire with more shielding is used for 2- to 3-meters and splitters
Two different splitters cables are offered up to 3-meters for 1:2 400Gb/s 4-channel
and 1:4 200Gb/s 2-channel ends for use in ConnectX-7 and BlueField-3 adaptersBlueField-3 uses only QSFP112, and ConnectX-7 is offered in both QSFP112 and OSFP
DAC Twin-port OSFP Straight and Splitters using OSFP and QSFP112 Ends
ACC cables are used to extend the low-cost, low-power, and low latency of copper cables from 3- to 5-meters which can span several racks. ACCs are essentially DAC cables with an additional IC in each end to boost the signal power and noise reduction. This cable uses a pre-emphasis type of circuit, aka linear ACC, that learns the noise signal and inverts it before sending down the cable creating an anti-noise. The noise and anti-noise energies cancel each other out preserving the data signal. Unlike HDR/200GbE ACCs that use DSPs, pre-emphasis ACCs have very low power and low latency.
ACC configuration shadows the DAC line at longer lengths.
Offered in twin-port OSFP, OSFP, and QSFP112 ends.
ACCs offer length of up to 3-meters for the straight cables, and 4- and 5-meters for splitters.
Power consumption is 1.5 Watts on the 8-channel ends, and 0.6W and 0.3W on the split ends.
Thin 30AWG wire is used for short lengths of 3- and 4-meters.
Thicker 26AWG wire with more shielding is used for 5-meter splitters.
Two different splitter cables are offered up to 3-meters for 1:2 400Gb/s 4-channel and 1:4 200Gb/s 2-channel ends for use in ConnectX-7 and BlueField-3 adapters.
BlueField-3 uses only QSFP112, and ConnectX-7 is offered in both QSFP112 and OSFP.
ACC Twin-port OSFP Straight and Splitters OSFP and QSFP112 Ends
DACs and AOC splitters are offered for backwards compatibility by downshifting the modulation rate of switches to 50G-PAM4 enabling links Quantum-2 and SN5600 OSFP Ethernet switches to link to 200G HDR Quantum QSFP56 and Spectrum-3 switches and to 50G-PAM4 based ConnectX-6 and BlueField-2 DPUs using QSFP56 connector.
50G-PAM4 DACs
1:2 DAC splitters using twin-port OSFP 2x200G-to-two 200G QSFP56s based on 4x50G-PAM4 are offered from 1- to 2-meters.
As DACs are simply a bunch of wires, they can be downshifted to 2x 100GbE or HDR100 rates by the switch.
The 1:2 DAC splitter also supports 2x100G-to-two 100Gb/s QSFP56 links as 4x25G-NRZ ends for standard 100GbE and EDR rates.
A 1:4 DAC splitter is offered with 2x200G-to-four 100Gb/s using QSFP56 based on 2-channel 50G-PAM4 ends for 100G but does not support 4x25G-NRZ.
50G-PAM4 AOCs
1:2 AOC splitters using twin-port OSFP 2x200G-to-two 200G QSFP56s based on 50G-PAM4 is offered up to 30-meters for linking 400GbE/NDR switches to HDR/200GbE switches, adapters. In the Quantum-2 and Spectrum SN5600 switches, the 8-channel cages are down shifted to 50G-PAM4 modulation and split into 1:2 200Gb/s using QSFP56. This AOC can also support 200G-to-two 100Gb/s QSFP56 links as 2x 50G-PAM4.
These 2 AOCs are the only optical links available to link between 100G-PAM4 OSFP and 50G-PAM4 QSFP56 systems as separate transceivers are not available.
DACs and AOCs for backwards compatibility to HDR/200GbE, HDR100 and EDR/100GbE
No AOCs for 100G-PAM4 Series
AOCs consist of two or more transceivers with the fibers bonded inside and not detachable. This creates and entire, plug-and-play cable assembly like copper cables but at much longer lengths. While used extensively in EDR, HDR and 100GbE, 200GbE systems, AOCs are not offered for 100G-PAM4 Ethernet or InfiniBand systems. The twin-port OSFP and OSFP ends are heavy and very likely to break the fibers during installation. An 800G-to-4x 200G AOC would have five large OSFP connectors.
Additionally, complex fiber infrastructures are better addressed with connectorized fibers, and they can support future line rate upgrades with minimal changes.