During a data-center expansion, a systems administrator is installing a rack-mount server whose NIC exposes two QSFP+ ports. The server must connect to a top-of-rack 40 GbE switch located about 2 m away in the same cabinet. Management wants the lowest-cost, lowest-power cabling that still delivers full 40 Gbps throughput. Which cabling solution should the administrator deploy?
Passive QSFP+ direct-attach twinax copper cable
OM4 multimode MPO fiber with QSFP-40G-SR4 transceivers
Single-mode duplex LC fiber with QSFP-40G-LR4 transceivers
QSFP+ active optical cable (AOC) rated for up to 100 m
Passive QSFP+ direct-attach copper (DAC) cables are purpose-built for very short in-rack runs-typically 0.5 m to 5 m on passive twinax-and provide the full 40 Gbps data rate with almost no additional power draw or optical components. Active optical cables (AOC) and SR4 multimode fiber require integrated or external optics that add both cost and power, and they are designed for tens to hundreds of meters rather than a 2 m jumper. LR4 single-mode fiber is intended for long-haul links up to 10 km and is the most expensive option, making it inappropriate for an in-rack connection.
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