The QSFP28 100G Active Optical Cable is a specific and extremely common type of high-speed data center cable. Let's break down exactly what it is, its advantages, and where it's used.
What is a QSFP28 100G AOC?
It's a single, integrated assembly that combines four channels of optical transceivers (in the QSFP28 form factor) permanently attached to a multimode fiber optic cable. It's designed for short-range, high-bandwidth connections primarily within a data center rack.
✅ QSFP28: The form factor of the connector.
✅ QSFP = Quad (4) Small Form-factor Pluggable
✅ 28 = Supports data rates up to 28 Gbps per lane. For 100G, it uses 4 lanes at 25G or 28G.
✅ 100G: The total aggregate data rate is 100 Gigabits per second (Gbps).
Active Optical Cable (AOC): The transceivers convert electrical signals to optical signals (light) and back, requiring power from the switch. The cable is permanently attached, making it a simple plug-and-play solution.
✅ Technology: Uses VCSEL (Vertical-Cavity Surface-Emitting Laser) lasers at the 850nm wavelength.
✅ Fiber Type: Contains multimode fiber (typically OM3 or OM4) inside the cable jacket.
✅ Data Channels: 4 independent transmit and 4 independent receive channels (4x25G).
✅ Typical Reach: Up to 100 meters with OM4 fiber. Common lengths are 1m, 3m, 5m, 7m, 10m, 15m, 20m, 30m, 50m, and 100m.
✅ Protocols: Primarily used for 100GBASE-SR4 Ethernet, but also used in InfiniBand EDR and proprietary storage interconnects.
Advantages of QSFP28 AOCs
🔹 Simplicity & Reliability: A single, pre-terminated unit eliminates the risk of dirty or misaligned fiber connectors, a common point of failure. It's truly plug-and-play.
🔹 Longer Reach than DACs: They can easily reach 100m, while Direct Attach Copper (DAC) cables are limited to about 3-5m.
🔹 Lightweight and Flexible: The fiber cable is much thinner, lighter, and more flexible than a thick copper DAC, drastically improving cable management and airflow in dense server racks.
🔹 Immunity to EMI: Being optical, they are completely immune to electromagnetic interference (EMI), which is crucial in noisy data center environments.
🔹 Lower Power: They consume less power (typically 1.5W - 3W per end) than a solution using separate optical transceivers.
🔹 Cost-Effective: For distances beyond 3-5 meters, AOCs are often more cost-effective than buying two separate QSFP28 transceivers and a duplex fiber patch cable.
Where is it Used?
✅ QSFP28 100G AOCs are the workhorse for modern data center connectivity:
✅ Connecting top-of-rack (ToR) switches to leaf or spine switches.
✅ Connecting high-performance servers and storage arrays to the network.
✅ Inter-switch links (ISLs) within a rack or between adjacent racks.
✅ High-Performance Computing (HPC) and AI clusters.
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