The following lists considerations for various direct attach copper (DAC) cable usage scenarios.
| Cable Type | ||
|---|---|---|
| Consideration | QSFP-DD | QSFP+/QSFP28 |
| Lanes of connectivity | 8 lanes of connectivity span 2 GTF quads. | 4 lanes of connectivity to a single GTF quad. |
| Legacy / DD support | Consists of legacy pins (lanes 1-4) and DD pins (lanes 5-8). | Connects only to the legacy pins (lanes 1-4) of the QSFP-DD connector. |
| Legacy pin connection | Legacy pins are connected to quads 127 and 130 (QSFP 1 and 2) | Connect to quads 127 and 130 (QSFP 1 and 2). |
| DD pin connections | DD pins are connected to quads 128 and 131. | Not connected |
| Card jitter attenuation support | Provides access to jitter cleanup device via dedicated REFCLK outputs on quads 127 and 130 (QSFP-DD 1 and QSFP-DD 2), or via HPIO (bank 65). | Requires use of HPIO (bank 65) to provide recovered clock to jitter cleanup device. |
Suggested DAC Cables
Any industry standards compliant QSFP+/QSFP28/QSFP-DD DAC cable can be used with the above mentioned considerations. The Amphenol-branded cable is suggested for a QSFP-DD to 8xSFP+ splitter DAC cable.