2026 Guide to High-Speed Direct Attach Cables (DACs) for Data Center Interconnection

Introduction

Modern data centers, clouds, and AI clusters are hungry for bandwidth:

• 10G/25G to servers is standard.
• 100G/200G/400G dominates leaf-spine fabrics.
• 800G and beyond are entering leading-edge environments.

For all this, you don't always need a full optical module plus separate fiber. For short-reach, high-density, low-power links, Direct Attach Cables (DACs) and Active Optical Cables (AOCs) remain incredibly important in 2026.

This guide will walk through:

• What DACs are and how they differ from AOCs and traditional optical modules.
• Passive copper DAC vs active copper DAC vs AOC: reach, power, cost, and use cases.
• How DACs fit into ToR, leaf-spine, AI/GPU pods, and short-range DCI.
• Practical design considerations: signal integrity, cable management, multi-vendor compatibility.
• Example deployment patterns and an advanced FAQ.

What is a DAC? - Fundamentals in 2026

Definition and Basic Construction

A Direct Attach Cable (DAC) is a factory-terminated high-speed cable assembly that behaves like "fixed" transceivers with a permanently attached copper or fiber cable.

Key characteristics:

• Media: Copper DAC: shielded twinax conductors (typically 24-30 AWG). AOC: multimode fiber inside a cable with integrated optics at each end.
• Ends: Integrated pluggable connectors with the same form factors as optical modules, for example: SFP+ / SFP28 (10G / 25G) QSFP+ / QSFP28 / QSFP56 (40G / 100G / 200G) QSFP-DD / OSFP (200G / 400G / early 800G cases)
• Lengths: Copper DACs: typically 0.5-1 m up to ~5-7 m (sometimes more with active DACs). AOCs: typically 3-100 m, depending on speed and design.

The key idea: instead of buying separate transceivers and cables, you get a single integrated assembly that plugs directly into your switch/NIC ports.

DAC vs AOC vs Optical Transceiver + Fiber

At a high level:

• Passive Copper DACVery short distance, lowest cost, lowest power, nearly zero added latency. Ideal for intra-rack or adjacent rack applications.
• Active Copper DACCopper cable with active signal conditioning electronics at the ends. Extends reach beyond passive limits while staying cheaper than full optics.
• Active Optical Cable (AOC)Fiber-based DAC with integrated optics inside the connector housings. Provides longer reach (tens of meters) and slim, lightweight cabling.
• Optical module + fiberFully modular: replace fiber or module independently. Supports the widest range of distances and link types (from meters up to kilometers).

Each has a sweet spot. DACs (copper and AOC) excel at short to medium distances with great density and low power per port. Optical modules and patch fiber dominate for longer reach or more flexible topologies.

Types of High-Speed Direct Attach Cables

Passive Copper DAC

Passive DACs are simply high-quality twinax cables with no active electronics in the connectors.

Pros:

• Ultra-low power (often no more than a few tens of milliwatts for EEPROMs, sometimes quoted as <0.1-0.3 W).
• Lowest cost per port at a given speed.
• Minimal added latency (no active components in the path).

Typical reach (rough rule-of-thumb, vendor-dependent):

• 10G SFP+: ~0.5-7 m
• 25G SFP28: ~0.5-5 m
• 40G/100G QSFP+ / QSFP28: ~0.5-3-5 m
• 200G/400G DAC: often 0.5-2-3 m, depending on the platform and cable quality

The exact supported lengths depend on:

• Switch/NIC SerDes capabilities
• FEC (Forward Error Correction) options
• Signal integrity budgets per platform

Active Copper DAC

Active DACs include small signal conditioning chips in the connector housings:

• Techniques like equalization, pre-emphasis, or FEC-friendly tuning help compensate losses in the copper cable.

Pros:

• Extended reach compared to passive DACs at the same speed.
• Still lower power and cost than full optical modules.

Cons:

• Higher power per port than passive DAC.
• Slightly more expensive and complex.

Typical usage:

• When you need to stretch copper connections slightly beyond passive limits, but still want to avoid going optical.

Active Optical Cable (AOC)

An AOC is a fiber-based DAC: the optical engine and fiber are built into a single assembly.

Pros:

• Much longer reach than copper DAC for many speeds: Often 10-30-100 m (depending on speed and design).
• Very slim, light, and flexible, helpful in high-density racks.
• Power per port typically lower than discrete transceivers + fiber, but higher than passive copper.

Cons:

• Higher cost than passive DAC; generally cheaper than module+fiber for short-medium distances.
• You cannot separate the optics from the cable (if one side fails, the whole assembly is replaced).

AOCs are ideal when you need longer than copper but shorter than "typical long-haul optics", with good cable manageability.

DAC vs Optical Transceiver + Fiber - Detailed Comparison

Comparison Table (Reach / Power / Flexibility / Cost / Use Cases)

Below is a conceptual comparison (actual values vary by vendor/model):

When to Choose DAC/AOC vs Modules + Fiber

A rough rule-of-thumb:

• Inside a rack / same cabinet: Passive DAC first choice.
• Between neighboring racks or within a row: Active DAC or AOC depending on distance and layout.
• Between rows, pods, or rooms within a DC: AOC or SR/DR optics + fiber.
• Between buildings or long distances: Optical transceivers + single-mode fiber.

Performance, Reach, and Power - Copper DACs vs AOCs vs Optics

Typical Reach by Speed and Cable Type

Exact numbers depend strongly on vendors and platforms, but typical ranges look like:

• 10G SFP+ DACPassive: ~0.5-3-7 m Active: up to ~10 m in some cases
• 25G SFP28 DACPassive: ~0.5-3-5 m Active: up to ~5-7 m
• 40G QSFP+ / 100G QSFP28 DACPassive: ~0.5-3-5 m Active: slightly further depending on SerDes and cable design
• 200G QSFP56 / 400G QSFP-DD / OSFP DACPassive: often ~0.5-2-3 m, sometimes up to 5 m Beyond that: AOC or optical modules are typically required
• AOCs10G-400G: commonly sold in lengths from a few meters up to 30-100 m+
• Optical modules + fiberRanges from: Datacenter MMF (e.g. 100G SR4): up to 70-100 m on OM3/OM4. Single-mode short-reach links (e.g. 100G DR/FR, 400G DR4/FR4): up to hundreds of meters or a few km. Long-haul DWDM: many kilometers.

Power Consumption and Thermal Impact

General power hierarchy (lowest to highest):

1. Passive copper DAC
2. Active copper DAC
3. AOC
4. Optical transceiver + fiber

Lower power per port means:

• Less heat inside high-density switches and NICs.
• More capacity in constrained power envelopes.
• Lower total energy cost at scale.

For dense top-of-rack deployments, using DACs where possible can save meaningful watts per port across tens or hundreds of switches.

Cost and Density Considerations

• DACs: Lowest up-front cost per port for short links. Perfect when you know the port-to-port distance will remain within their reach limits.
• AOCs: More expensive than DACs, but cheaper than separate optics+fiber in many short-to-medium reach cases. Much better for cable routing, density, and airflow.
• Optical modules + fiber: Highest cost, but provide maximum flexibility: You can reuse fiber for future upgrades. You can swap modules without replacing cable.

In practice, most modern designs use a mix:

• DACs inside racks and neighboring racks.
• AOCs for longer in-row or adjacent row connections.
• Optics + fiber for between-pod, between-room, or between-building links.

Form Factors and Speed Generations - 10G to 400G (and Beyond)

1. 10G & 25G: SFP+ and SFP28 DAC

• 10G SFP+ DAC: Classic ToR-server and switch-switch stacking solution.
• 25G SFP28 DAC: Dominant for newer servers and storage nodes. Higher efficiency (25G per lane) and used in 100G (4×25G) and 50G/200G designs.

2. 40G & 100G: QSFP+ and QSFP28 DAC

• 40G QSFP+ DAC: Common in older or transitional leaf-spine and aggregation layers.
• 100G QSFP28 DAC: Today's staple for short-range 100G fabric links between switches. Also used as breakouts (e.g., 100G→4×25G) to aggregate server connections.

3. 200G & 400G: QSFP56, QSFP-DD, OSFP DAC

• 200G QSFP56 DAC: Used where 200G per port is needed between leaf-spine or within AI pods.
• 400G QSFP-DD/OSFP DAC: Emerging standard for next-gen leaf-spine and AI cluster fabrics.

At these speeds:

• Copper constraints are tighter; passive DAC reach is typically shorter.
• Platform DAC support lists become very important.

4. Breakout DACs

Breakout DACs connect a higher-speed port to several lower-speed ports, for example:

• 40G QSFP+ → 4×10G SFP+
• 100G QSFP28 → 4×25G SFP28
• 200G/400G DAC breakouts (e.g., 4×50G or 4×100G)

Typical use cases:

• ToR port at 100G splitting to multiple 25G server NICs.
• Spine or core port aggregating multiple lower-speed links.

DACs in Modern Data Center Architectures (Leaf-Spine, AI Clusters, DCI)

1. Top-of-Rack (ToR) to Server Connections

This is the classic DAC use case:

• 10G SFP+/25G SFP28 DAC from ToR switch → server NIC.
• In newer environments: 50G/100G DAC for higher-performance servers.

Typical distance: 1-3 meters, sometimes up to 5 meters for tall racks or special layouts.

Benefits:

• Lower latency (no optical conversion).
• Lowest power and BOM cost.
• Fewer components to fail or mis-match (no separate optics and fiber).

2. Leaf-Spine and Spine-Super-Spine Links

For links within the same row or neighboring rows:

• Short leaf-spine connections, especially when switches share a rack or are in adjacent racks, are great candidates for 100G/200G/400G DACs.
• If the distance grows or routing is complex, AOCs become attractive.
  

A common pattern:

• Passive DAC up to 2-3 m.
• Active DAC or AOC for up to tens of meters.
• SR/DR optics + MMF/SMF beyond that.

3. AI/GPU Cluster Interconnects

High-performance AI and GPU clusters require:

• Very high bandwidth (100G, 200G, 400G per port or more).
• Many parallel links between GPU nodes and fabric switches.
• Minimal latency and predictable behavior.

In these pods:

• 400G QSFP-DD DACs may be used between GPU nodes and ToR/leaf switches when they are in the same rack.
• 400G AOCs are common between adjacent racks where copper isn't practical.

Key considerations:

• Physical cable bulk: heavy copper DACs vs slender AOCs.
• Airflow and hot aisle conditions.
• Ease of re-cabling when the GPU fleet is reconfigured.

4. Short-Reach Data Center Interconnect (Intra-DC DCI)

Within the same facility (e.g., between cages or rows in the same hall):

• DAC or AOC can be used for short-range DCI if distances are modest.
• For longer in-building DCI or between buildings, optical modules + SMF are typically required.

Using DACs/AOCs for intra-facility DCI saves power and cost, as long as distance and cable routing allow.

Design Considerations for DAC Deployment in 2026

Signal Integrity, FEC, and Host Compatibility

High-speed signals over copper require:

• Tight control of channel loss and impedance.
• Proper FEC (Forward Error Correction) on the host.

Key points:

• As SerDes speeds increase (25G NRZ, 50G/100G PAM4), the maximum passive DAC length tends to decrease.
• Some platforms officially support only certain lengths and brands of DAC at particular speeds.

Always check:

• The switch/NIC's DAC compatibility list.
• Recommended maximum lengths for each speed and form factor.

Cable Management, Bend Radius, and Airflow

Copper DAC characteristics:

• Thicker and heavier than fiber.
• Larger minimum bend radius.
• Can impede airflow if not carefully managed.

AOCs:

• Much thinner and lighter.
• Easier routing in dense racks and through cable managers.
• Better for maintaining airflow and reducing mechanical strain.

In high-density racks, a mix of DAC (for shortest links) and AOC (for more complex routing) often yields the best balance of cost, manageability, and cooling.

Interoperability and Vendor Lock-In

DACs typically contain EEPROMs that:

• Advertise supported speed, cable type, length, and vendor information.
• Can be coded to specific vendors (Cisco, Huawei, Ruijie, H3C, etc.) or coded generically.

Consider:

• Whether your environment requires vendor-specific coded DACs.
• Or if you can use multi-vendor compatible DACs to reduce cost and simplify inventory.

A partner like Network-Switch.com can supply DACs coded for multiple vendors or NS-branded DACs compatible with your hardware to avoid unnecessary lock-in.

Example Deployment Patterns with DACs

1. ToR to Server Connectivity

Example:

• A rack with a 25G SFP28 ToR switch (Cisco/Huawei/Ruijie/H3C/NS) and multiple 25G server NICs.

Design:

• Use 25G SFP28 passive DACs for server connections within the same rack.
• For servers in adjacent racks (slightly longer runs), consider active DACs or AOCs.

Benefits:

• Low cost per link.
• Simple cabling; fewer components than optics + fiber.
• Easy to aggregate multiple 25G links into 100G fabric uplinks.

2. Leaf-Spine Interconnects

Example:

• 100G QSFP28 leaf & spine switches in the same row.

Design:

• For leaf-spine pairs in the same/adjacent racks: Use 100G QSFP28 passive DACs where lengths are short.
• For slightly longer links: Use AOCs or SR4 optics + OM4 fiber.

This mix minimizes costs and power while preserving flexibility for reconfiguration.

3. GPU/AI Pod Interconnects

Example:

• AI cluster with 400G QSFP-DD switches and GPU nodes.

Design:

• For GPU nodes co-located in the same rack: Use 400G DACs to connect GPUs to leaf/TOR.
• For pods spanning multiple racks: Use 400G AOCs for better cable manageability and airflow.

This keeps copper where it's short and efficient, and fiber where routing and cooling matter most.

FAQs

Q1: How do I choose between passive DAC, active DAC, and AOC for a given link?

A: 

• Passive DAC if: The distance is short (e.g., ≤3-5 m) and platform supports it. You want lowest cost and power.
• Active DAC if: You want to extend reach over copper a bit further while staying cheaper than optics.
• AOC if: You need longer reach (up to tens of meters), lighter cable, and easier routing. Thermal and cable bulk are concerns.

Q2: What is the maximum recommended distance for 10G/25G/100G/400G passive DAC?

A: It depends on platform and cable quality, but typical guidelines:

• 10G SFP+ DAC: 3-7 meters
• 25G SFP28 DAC: 3-5 meters
• 100G QSFP28 DAC: 2-5 meters
• 200G/400G DAC: often 1-3 meters

Always check the switch/NIC vendor's datasheet and DAC compatibility matrix.

Q3: Are DACs more reliable than separate optics + fiber for short links?

A: For very short links inside a rack:

• DACs remove one set of connectors and a separate fiber patch, so they can be simpler and less error-prone.
• There's no risk of mixing fiber types or polarity on patch cords.

However, reliability in practice will depend on:

• Cable quality.
• Correct coding and compatibility.
• Proper strain relief and cable management.

Q4: How does DAC power consumption compare with optical modules at scale?

A: Per port:

• Passive DAC: typically <<1 W per end.
• AOC: around 1-2 W per end (varies).
• Optical modules: often several watts per end (depends on type and speed).

At a scale of hundreds or thousands of ports, choosing DAC/AOC where appropriate can save hundreds of watts or more, which translates to:

• Lower electricity cost.
• Less heat and cooling demand.

Q5: Do 400G DACs support breakout (4×100G or 8×50G), and what are the trade-offs?

A: Yes, many 400G DACs support breakout modes:

• 400G→4×100G (e.g., QSFP-DD to 4×QSFP28).
• 400G→8×50G in some designs.

Trade-offs:

• Very strict limits on length and platform compatibility.
• Heavier and stiffer cables.
• Important to verify breakout mode support on both the 400G port and the lower-speed ports.

Q6: How do I confirm if a DAC is compatible with my switch or NIC?

A: Check:

1. The form factor (SFP+/SFP28/QSFP+/QSFP28/QSFP-DD/etc.).
2. The speed and coding (e.g., 25G NRZ vs 50G PAM4 lanes).
3. The vendor's supported DAC list for that platform.
4. Whether you require vendor-coded DACs (e.g., Cisco-coded, Huawei-coded) or if multi-vendor NS-branded DACs are accepted.

Network-Switch.com can supply DACs coded for specific vendors or tested for multi-vendor compatibility.

Q7: When should I choose AOC instead of copper DAC in a dense rack?

A: Choose AOC instead of copper DAC when:

• You have many high-speed links and the copper bundle becomes too bulky, obstructing airflow or complicating cable management.
• The link length is near the limit of what DAC can reliably support.
• You want lighter cables that are easier to route and maintain.

Q8: Can I mix DACs from different vendors in the same fabric, or should I standardize?

A: You can mix DACs from different vendors as long as each cable is supported by the platforms it connects to. In practice:

• Some operators prefer to standardize for simplicity.
• Others use multi-vendor DACs to reduce cost and avoid lock-in.

The key is to ensure:

• Proper coding (EEPROM IDs).
• Compliance with electrical specifications.
• Adequate testing in your environment.

Q9: What should I watch out for when designing DAC-heavy cabling in hot aisles?

A: Watch for:

• Cable bulk that restricts airflow at the back of the rack.
• Bends that approach or exceed minimum bend radius.
• Excessive stacking or pinching around PDUs and cable managers.

Mitigations:

• Use AOCs where routing is complicated.
• Plan cable paths with airflow in mind.
• Use proper cable management hardware (ladders, guides, Velcro instead of zip ties).

Q10: How can Network-Switch.com help me validate my DAC selection and topology before deployment?

A: Network-Switch.com can:

• Review your intended fabric topology (ToR/leaf-spine/AI pods/DCI).
• Map your switch and NIC ports (Cisco, Huawei, Ruijie, H3C, NS, etc.) to appropriate DAC/AOC/optical options.
• Recommend specific lengths, cable types, and coding to ensure compatibility.
• Provide a validated BOM that balances cost, power, density, and future growth.

This de-risks deployment and saves time during installation.

Why Choose us for DAC, AOC, and Optical Interconnect Solutions?

1. Multi-Vendor, Multi-Generation Support

We support:

• Major switch and adapter vendors: Cisco, Huawei, Ruijie, H3C, and more.
• NS-branded DACs and AOCs compatible with a wide range of platforms.
• Interconnect speeds from 10G to 400G, and planning for 800G-ready environments.

2. End-to-End Interconnect Design

Network-Switch.com can help you design:

• ToR-server interconnects using SFP+/SFP28 DACs and AOCs.
• Leaf-spine fabrics using 40G/100G/200G/400G DACs, AOCs, and optics.
• AI/GPU pod wiring with the right mix of 100G/200G/400G DACs and AOCs.
• Short-range intra-DC DCI where DAC/AOC may be enough.

We provide:

• Switches, NICs, DACs, AOCs, optical modules, and fiber cables in one coherent, validated package.

3. Engineering Consultation and Validation

Our engineers can:

• Validate distance and power constraints.
• Confirm compatibility and coding requirements.
• Help you balance DAC, AOC, and optical modules to optimize cost and complexity.

From initial design to expansion phases, we can be your long-term interconnect partner.

Conclusion

By 2026, high-speed Direct Attach Cables (copper DACs and AOCs) remain central to efficient data center design:

• Passive and active DACs deliver ultra-low-cost, low-power connectivity for short links.
• AOCs bridge the gap between DAC and full optics, offering longer reach with better cabling ergonomics.
• Traditional optical modules plus fiber still dominate where long distance and maximum flexibility are required.

The key is not "DAC vs optics" but finding the right mix for your topology:

• DAC inside racks and between adjacent racks.
• AOC or short-reach optics across rows or within halls.
• Longer-reach optics for pod-to-pod, room-to-room, or building-to-building links.

With the help of Network-Switch.com's multi-vendor interconnect solutions and engineering expertise, you can design a network fabric that is:

• Cost-efficient
• Power-efficient
• Scalable
• Ready for 10G-400G today and 800G tomorrow

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