DAC Cable is becoming a standard choice for high speed data center interconnection, especially for short links between servers, switches and storage. In this article, you'll quickly understand what DAC Cable is, the differences between passive DAC, active DAC and AOC, and how high speed DAC cable compares with traditional optical transceiver solutions in terms of cost, power and distance.
You'll also see how Hengtong data center DAC cable products cover 10G to 400G applications such as ToR, Spine-Leaf and short-reach DCI, and get practical guidance on how to choose the right DAC Cable type and length for your own racks.
DAC Cable Types – Passive, Active and AOC
Passive DAC Cable
A passive DAC Cable is the simplest and most cost-effective type of direct attach cable. Inside the assembly, the high speed lanes are implemented with shielded twinax copper conductors, typically in 24–30 AWG, and the connectors contain no active components such as equalizers or drivers. The host PHY on the switch or server fully handles signal conditioning.
Key technical points for passive DAC Cable:
Typical gauges:
- 30 AWG for very short links (0.5–2 m)
- 28/26 AWG for 3–5 m links
- 24 AWG for demanding 5–7 m links at higher data rates
In the data center, passive DAC Cable is ideal for:
- Server to ToR switch connections inside the same rack
- Adjacent rack connections where the physical distance is limited
- High-density environments where every watt matters and short passive links can significantly reduce rack-level power.
For these reasons, passive DAC Cable is often the first choice whenever the channel loss and distance budget allow it.
Active DAC Cable
An active DAC Cable integrates signal conditioning circuitry such as linear equalizers or retimers inside the connector shells at one or both ends. The copper twinax cable itself is similar to passive DAC, but the active components extend the usable reach and improve margin at higher data rates (especially for 25G, 50G and PAM4-based 100G/400G lanes).
Key technical points for active DAC Cable:
Power consumption: typically around 0.5–1 W per end, depending on data rate and implementation
Typical reach:
Commonly 5–10 m for 25G/100G links
In favorable conditions and lower data rates, can extend beyond 10 m
Performance benefit:
- Better eye diagram and higher link margin on marginal channels
- Can relax requirements on AWG and routing path compared to passive DAC
Typical use cases for active DAC Cable in data centers:
Rack-to-rack connections within the same row where the distance is beyond passive DAC limits
Leaf–Spine links in compact rows where copper is still preferred for cost or EMI reasons
Scenarios where existing trays or routing paths result in slightly longer or more lossy copper channels.
When you need more reach than a passive DAC Cable but still want to keep the copper cost advantage, an active DAC Cable is usually the right compromise.
AOC – Active Optical DAC Cable Assemblies
Active Optical DAC Cable Assemblies (more commonly called AOC) take the DAC concept and replace the copper twinax with multimode optical fiber inside the cable. Each end of the AOC integrates a full electrical-to-optical and optical-to-electrical conversion engine, but from the host perspective it behaves like a standard high speed pluggable interface.
Key technical points for AOC DAC Cable assemblies:
- Medium: multimode fiber (e.g. OM3/OM4/OM5)
- Typical reach: 30–100 m within a data center, depending on data rate and fiber type
- Power consumption: generally in the 0.5–1 W range per end, still lower than many discrete optical transceiver solutions
Mechanical advantages:
- Much lighter than copper DAC Cable over the same distance
- Smaller bend radius and easier cable management in overhead trays or underfloor pathways
In practice, AOC DAC Cable assemblies are perfect when:
You need to span longer distances inside the data center, such as between rows or between rooms
The cable routes are complex, with multiple bends and limited space
You want to maintain a DAC-style "one part number, one link" approach but with optical performance.
How to Choose the Right DAC Cable Type
For most projects, you can start with a simple distance-based rule and then refine based on topology, power and routing constraints:
| Link Distance (typical) | Medium | Recommended Type | Typical Scenario |
|---|---|---|---|
| 0.5–3 m | Copper twinax | Passive DAC Cable | Server to ToR within the same rack |
| 3–7 m | Copper twinax | Passive or Active DAC Cable | Server/ToR to adjacent rack |
| 5–10 m | Copper twinax | Active DAC Cable | Rack-to-rack in the same row |
| 10–30 m | Copper or fiber | Active DAC Cable / AOC DAC Cable | Leaf–Spine in compact data halls |
| 30–100 m | Multimode fiber | AOC DAC Cable Assemblies | Row-to-row, room-to-room, short-reach DCI |
A practical selection approach:
Start with passive DAC Cable if the distance is short and the equipment supports it – this minimizes cost and power.
Move to active DAC Cable when the reach or channel loss is slightly beyond passive capability but you still want copper.
Choose AOC DAC Cable assemblies when the path is long, complex, or when weight and bend radius become critical.
Hengtong can help evaluate your link budget, routing and topology to recommend the optimal combination of passive DAC Cable, active DAC Cable and AOC DAC Cable for each part of your data center network.
DAC Cable vs Optical Transceiver – Which Is Better for Short-Reach Links?
Reach and Topology – Where DAC Cable Fits Best
From a topology point of view, DAC Cable is optimized for short-reach, high-density links inside a single data hall:
DAC Cable reach
Copper DAC Cable: typically up to 5–7 m (passive) and about 10–15 m (active)
AOC DAC Cable assemblies: typically 30–100 m inside the data center
Typical DAC Cable topologies
- ToR server access: server ⇔ ToR switch in the same rack
- Adjacent racks: ToR ⇔ ToR or ToR ⇔ aggregation within a few racks
- Middle-of-Row / End-of-Row: Leaf ⇔ Spine when rows are relatively compact
By contrast, optical transceivers + fiber patch cords are designed for longer-reach and more diverse topologies:
Standardized distances from 100 m over MMF all the way to 10–40 km or more over SMF, depending on the transceiver type
Typical for inter-room, inter-building or even metro-scale connections, where copper DAC Cable is no longer feasible
In other words, if your link stays inside or between racks within the same row, DAC Cable is usually the natural fit; if it must cross rooms, floors or sites, optical transceivers become mandatory.
Power Consumption and Thermal Design
One of the biggest differences between DAC Cable and optical transceivers is power per port, which directly affects rack-level thermal design:
DAC Cable power profile
- Passive DAC Cable: almost zero additional power, typically <0.15 W per end
- Active DAC Cable / AOC: around 0.5–1 W per end, depending on data rate
Optical transceiver power profile
Many 10G/25G/100G pluggable modules operate in the 1–3 W range
High-end or long-reach 100G/400G modules can reach 4–5 W per port
In a 48-port ToR switch, replacing 48 optical transceivers with 48 high speed DAC Cable links can save dozens of watts. For dense Spine-Leaf fabrics or large-scale clusters, this translates into:
- Lower cooling demand per rack
- More headroom for future speed upgrades
- Better overall PUE at the facility level
This is why many operators prefer DAC Cable wherever reach allows, then reserve optical modules for the truly long paths.
Cost & Operational Simplicity
Beyond reach and power, DAC Cable delivers very tangible benefits in CAPEX and OPEX:
Hardware cost advantage
A single DAC Cable replaces both the optical transceiver and the patch cord
Especially at 10G/25G/100G, DAC Cable is often significantly cheaper per link than "transceiver + fiber"
Fewer SKUs, simpler inventory
Each link is one part number (e.g., "100G QSFP28 DAC Cable, 3 m")
No need to match transceiver type, fiber type and connector polish across multiple vendors
Lower risk of mis-patching
Fixed assemblies mean you cannot mix the wrong transceiver and cable type
Length is controlled from day one, which helps with clean cable management and predictable performance
For short-reach data center interconnection, these factors add up quickly across thousands of ports. You save on initial investment, reduce spare stock complexity, and make rollout and troubleshooting easier for on-site teams.
For short-reach data center interconnection, DAC Cable is often the most cost-effective option, while optical transceivers remain the right tool for long-distance and highly flexible connectivity requirements.
How DAC Cable Powers High Speed Data Center Interconnection
DAC Cable plays a key role in optimizing high-speed, short-distance connections within the data center, providing an efficient and cost-effective solution for a variety of interconnection scenarios. Below are the primary applications where DAC Cable drives performance and simplifies data center infrastructure.
Top-of-Rack DAC Cable Connections
In many data centers, Top-of-Rack (ToR) switches serve as the central hub for connecting multiple servers within a single rack. For short-range connections between servers and the ToR switch, DAC Cable provides an ideal solution.
Server ⇔ ToR Switch: For distances between 1–3 m, passive DAC Cable is highly recommended due to its low power consumption and cost-effectiveness.
Passive DAC Cable helps achieve:
Low power consumption: Typically <0.15 W per end
Quick deployment: No need for fiber optic transceivers, just plug and play
Compact and reliable links with low latency
This configuration is common in dense rack environments where space and power efficiency are crucial.
Spine-Leaf Interconnect with High Speed DAC Cable
As data center networks scale, Spine-Leaf architecture is widely used for high-performance interconnection. High-speed DAC Cable facilitates efficient communication between Leaf and Spine switches, ensuring low-latency, high-bandwidth links across the network fabric.
Leaf ⇔ Spine: Typically in the 3–30 m range, 40G/100G/200G/400G DAC Cable or AOC can be used depending on the required bandwidth and distance.
40G/100G DAC Cable: Ideal for high-performance interconnects within the same row or across adjacent rows in a compact topology.
200G/400G DAC Cable: Suitable for high-capacity links between larger, higher-density switches.
The use of DAC Cable here offers:
High density with minimal power consumption
Cost-effectiveness compared to fiber-based alternatives
Simplified cable management, with fewer connectors and components
Short-Reach DCI Using 400G DAC Cable and AOC
In modern data centers, short-reach DCI (Data Center Interconnection) between different rooms or across campuses is often necessary. High-speed 400G DAC Cable and AOC solutions enable seamless communication between data center buildings or floors within the same campus.
100G/400G DAC Cable + AOC: For interconnecting different rooms, floors, or buildings within the same data center, these cables can cover distances from 30 m to 100 m, providing low-latency, high-capacity links.
This configuration is often used for:
Data center-to-data center communication within a campus or across interconnected sites
Enabling higher bandwidth interconnects without the cost and complexity of long-range fiber solutions
By using DAC Cable and AOC, data centers can optimize for both high performance and flexibility, maintaining seamless connectivity across short-range DCI.
In conclusion, DAC Cable is a versatile solution for short-reach data center interconnections, providing reliable, efficient, and cost-effective links for both server-to-switch and high-performance switch interconnects across different data center topologies.
DAC Cable FAQ
Here are some frequently asked questions about DAC Cable and its applications in data centers:
What is a DAC Cable and when should I use it in my data center?
A DAC Cable (Direct Attach Cable) is a pre-terminated, factory-assembled cable that connects servers, switches, and storage devices with fixed, pluggable connectors. It is typically used for short-reach interconnection (1–100m), such as server-to-switch or switch-to-switch connections within racks or between adjacent racks. DAC cables are ideal for high-density, low-power, and cost-effective interconnect solutions.
What is the maximum length of a copper DAC Cable and an AOC?
Copper DAC Cable: The maximum reach is typically 5–15 meters depending on the data rate and whether the cable is passive or active.
AOC (Active Optical Cable): AOC cables, which use optical fiber, can typically reach 30–100 meters, providing a longer-distance alternative when copper is not feasible.
What is the difference between passive DAC Cable and active DAC Cable?
Passive DAC Cable: Does not contain any active components, making it more energy-efficient and cost-effective. Typically used for shorter distances (up to 7 meters).
Active DAC Cable: Contains signal conditioning circuits (such as equalizers) that boost the signal, allowing for longer reach (up to 10-15 meters) and better performance at higher speeds (e.g., 100G and beyond).
Can Hengtong DAC Cable replace optical transceivers for short-reach links?
Yes, Hengtong DAC Cable can replace optical transceivers for short-reach connections (typically up to 100 meters) in data centers. DAC cables are an ideal, cost-effective solution when you need high-speed interconnects between devices within the same rack, adjacent racks, or within short-distance topologies.
Are Hengtong DAC Cables compatible with my existing switches and servers?
Hengtong DAC Cables are fully compatible with most major switch and server manufacturers. They follow industry standards such as SFP+, QSFP+, QSFP28, and QSFP-DD, ensuring seamless interoperability across a wide range of network equipment.
How to choose the right DAC Cable length and gauge (AWG)?
When selecting a DAC Cable, consider the following:
Length: Match the cable length to the physical distance between devices (server-to-switch, rack-to-rack, etc.). Typical ranges: 1–3m for within the same rack, 3–10m for between adjacent racks, 10–30m for longer interconnects.
AWG (Gauge): For longer distances or higher data rates, select thicker cables (lower AWG) for reduced signal attenuation. For short-range connections, 28 AWG or 30 AWG is sufficient.
Does Hengtong provide OEM/ODM DAC Cable services?
Yes, Hengtong offers OEM/ODM services for DAC Cables. We can customize the length, gauge (AWG), connectors, and even labeling to meet your specific needs. Whether for data center projects or large-scale deployments, we can provide tailored solutions that align with your requirements.