DAC vs AOC Cable: Which to Choose for Data Center Links

Nov 12 , 2026 1

TL;DR: DAC (Direct Attach Cable) and AOC (Active Optical Cable) both connect switches and servers over short distances, but they work differently. DAC is a passive copper cable that is cheaper and lower-latency, ideal for racks under 7 m. AOC uses fiber with built-in transceivers, reaching 30 m or more and immune to EMI. For short in-rack links, DAC wins on cost; for longer or electrically noisy links, choose AOC.

When you need to connect a switch to a server or another switch inside a data center, you do not always need separate transceivers and fiber patch cables. Two cable types — DAC and AOC — integrate the connection into a single cable. This guide explains the difference and when to pick each.

DAC vs AOC: How They Differ

• DAC (Direct Attach Cable): A copper twinax cable with SFP/SFP+/QSFP connectors permanently attached at both ends. It is passive (no electronics), so the signal travels over copper.
• AOC (Active Optical Cable): A fiber cable with transceivers permanently attached at both ends. It is active, converting electrical signals to light at each end.

Key Comparison

When to Choose Each

1. In-rack or adjacent-rack links (under ~7 m): DAC. It is cheaper, lower latency, and consumes less power. This covers most top-of-rack switch-to-server connections.
2. Longer links (7–30 m) or high EMI environments: AOC. The fiber medium reaches farther and is not affected by electrical interference.
3. High port density: DAC is often preferred because it draws no power and produces less heat than an AOC or a transceiver pair.

Real Cable Models You Can Match

Juniper's QFX line includes a full range of DAC cables that plug directly into SFP+ and QSFP ports, such as the QFX-SFP-DAC-1M, QFX-SFP-DAC-3M, QFX-SFP-DAC-5M and QFX-SFP-DAC-7M (copper SFP+ DACs in 1 m to 7 m lengths). For QSFP 40G links, matching QSFP DAC cables are used the same way. On the Cisco side, the equivalent part numbers follow the "SFP-H10GB-CU" naming convention for 10G copper cables.

The Bottom Line

For the vast majority of short data center links, a DAC cable is the cheapest and fastest option. Move to AOC only when distance or electrical noise pushes you past what copper can reliably handle. Matching the cable type and length to your actual rack layout avoids both overspending and under-provisioning.