Three ways to build the same logical link
A switch port can be connected with passive or active DAC, with AOC or with two separate transceivers and fibre cable. All can be correct – but for different distances and operating models. DAC uses copper and fixed connectors. AOC contains optics and fibre in a ready-made cable. Separate transceivers provide a modular link where cable and optics can be replaced individually.
The decision should be made per cable zone: within racks, between adjacent racks, between rows and between halls.
DAC: low power and simple economics at short distances
Passive DAC is often a strong choice for short links within racks or to adjacent equipment. It has low power consumption and few optical sources of error. The downside is thicker cable, limited range and that the entire cable must be replaced if a connector is damaged.
Check bend radius, cable diameter and airflow. A densely populated rack may have worse serviceability if the DAC cables become too many or too stiff. Active DAC can extend the range, but has electronics at the cable ends and must be supported by the platform.
AOC: more flexible fibre with fixed ends
AOC is thinner and lighter than DAC and often suits when the link is too long or the cable mass is too large for copper. Since the optics are integrated, no separate fibre specification is needed at installation. At the same time, the entire link becomes a spare part: if one end is damaged, the whole AOC is replaced.
AOC can be practical in standardised, predictable rack environments. In cable routes where pulling occurs through tight conduits, the fixed transceiver ends can, however, be a disadvantage.
Separate transceivers: greatest flexibility
Two transceivers and a separate patch cable give more combinations of range, fibre type and connector. It also simplifies troubleshooting and spare parts management when the same optics can be combined with different cable lengths. The downside is more components, more contact surfaces and often higher purchase costs.
For links between racks, zones or halls, the modular solution is often easier to document and repair. It becomes particularly relevant when permanent cabling and patching are to have different lifespans.
Calculate TCO – not just unit price
Include purchase price, power, cooling, installation time, cable management, spare parts and the cost of an outage. Over a few metres, DAC can be hard to beat. For longer links, AOC can reduce cable volume. In environments where quick fault isolation and reuse are highly valued, separate transceivers can provide lower overall risk.
- Create a simple standard: one approved link type per speed and length range. Avoid letting each installation become a new product choice.
Checklist before ordering
Verify port and coding at both ends, supported cable length, FEC and breakout mode, airflow and bend radius, cable path and fire class as well as how spare parts should be stocked. Label both ends with port, rack and link ID.
When this information accompanies the order, the compatibility check becomes quicker and the installation more predictable.
Frequently asked questions
Primarily for short, straight links where low power and low cost are significant and the cable mass is manageable.
The function is similar to an optical link, but AOC
is a combined unit where the ends are not swapped separately.
Separate transceivers and patch cables provide the clearest opportunity to replace one component at a time.