Optical Transceiver
What is DAC Cable? The Definitive Guide
Oct
Initial Published: May 5, 2017
Although DAC cables were widely used in data centers and computing networks, some are still unfamiliar with this term. So, what is a DAC cable?
DAC cable is a direct-attach copper cable with two specific connectors on both ends. It allows direct communication between networking devices over copper wire. As a networking engineer, I want to share my knowledge and help you understand the basics. In this guide, I compiled all the information regarding DAC cables.
Table of contents
Keep reading to learn more.
What is a DAC cable?
A DAC cable is short for direct-attach copper cable. It is a pre-terminated Twinax copper cable assembly with two pluggable connectors, connecting ports directly within active platforms such as networking switches, routers, servers, adapter cards, or data storage devices.
Take the SFP+ DAC cable as an example, shown in the picture below. It consists of a fixed-length (usually less than 7 meters) Twinax cable and two SFP+ transceivers. The four-pair copper cables were soldered to a circuit board of SFP+ transceivers, finally achieving a max bidirectional 10G high-speed rate.
What is a DAC Breakout Cable?
Sometimes, we classify a breakout cable as another DAC cable. The DAC breakout cable consists of one connector on one end but multiple (2 or 4) connectors on the other. Some users and vendors may also call it a Fanout DAC or Splitter DAC.
However, remember that these are the same product types, no matter how you call them. Do not get confused by the different terms.
In simple words, it splits one connector into multiple connectors. The one connector side provides a much higher speed (such as 40G), while the “split” ends at a lower speed (10G). Therefore, the breakout cable is useful for connecting different speed ports.
In some circumventions, the breakout DAC acts as an adapter to upgrade the low-speed ports to higher-speed ports and increase faceplate port density.
DAC Cable vs. Fiber
Fiber is a critical component of modern networks. Combined with fiber transceivers, it delivers a cost-effective ultra-high bandwidth networking transmission solution.
Unlike fiber cable and transceiver, direct-attach cable has advantages and disadvantages. Let’s make a simple comparison. It will help you make the right decision.
| Comparison | Fiber | DAC |
| Reach | max 160km | max 15m |
| Data Rate | 1G, 2.5G, 3G, 8G, 10G, 25G, 40G, 56G, 100G, 200G, 400G, 800G | 1G, 10G, 25G, 40G, 56G, 100G, 200G, 400G, 800G, 1.6T |
| DOM Support | Yes | No |
| Power Consumption | Higher | Lower |
| Weight | Lighter | Heaver |
| Price (Optcore) | Expensive Overall | Cheaper for short length |
| Size | Slim cables allow easy cable management and higher flexibility | Thicker cables, lower flexibility |
| Pros | Better EMI performance, much more choice, longer distance | Overall low cost, Better heat dissipation, better for short distance interconnectivity |
| Cons | Friendly budget | Limit distance, Bulky, difficult for cable management |
| Application | ToR, Middle of Row, End of Row, Zone to Zone | Top Of Rack/Middle Of Rack switches connected to End Of Row/Middle of Row switches |
Based on the table’s comparison, you should clearly understand their difference and advantages.
If you have a limited budget and do not care about cabling space, DAC is the better choice for very short-distance connectivity (typically less than 10 meters) in data centers and storage applications.
However, fiber cabling will provide better performance and be space-saving for longer-distance connectivity.
Consider it for the future and calculate the total cost if possible.
How do you classify DAC cables?
Based on the different benchmarks, we can divide them into different types.
We can divide signal conditioning functions into passive and active DACs based on availability.
Passive DAC Cable
A passive DAC does not contain electronics for signal conditioning and amplification. Therefore, it provides a lower price but a limited length (typically 7m for 10G). The passive cable will generate many bit errors over long distances.
Active DAC Cable
Active DAC contains a microprocessor and other electronics for signal conditioning and amplification, which provides better performance for longer-distance transmission.
Because of its additional electronics, the price is higher than that of passive cable and more expensive than AOC cable. Before you purchase an active cable, comparing the total cost with an AOC or optical transceiver will be better. You may find a better cost-saving solution.
Classified by Data Rate and Form Factor
- SFP DAC Cable: SFP to SFP, offers 1G speed for gigabit ethernet SFP port connectivity
- SFP+ DAC Cable: 10G SFP+ to 10G SFP+, suitable for SFP+ port connectivity. This type is the most popular copper cable with a relatively low price, widely used in data centers and enterprise networks.
- SFP28 DAC Cable: 25G SFP28 to 25G SFP28, which typically supports 25G speed for the SFP28 port, is usually used in a 25GbE Ethernet application.
- QSFP+ DAC Cable: 40G QSFP+ to 40G QSFP+, suitable for 40G QSFP+ port.
- 56G FDR DAC Cable: 56G QSFP+ to 56G QSFP+, providing 56G (4x14G) speed, suitable for InfiniBand in the enterprise data center.
- QSFP28 DAC Cable: This 100G QSFP28 to 100G QSFP28 cable provides 100G (4x25G) speed, suitable for high-speed connectivity in data centers and cloud computing.
- QSFP56 DAC Cable: 200G QSFP56 to QSFP56, support 200G (4x50G) speed.
- 400G QSFP-DD DAC Cable: 400G QSFP-DD to 400G QSFP-DD, supports 400G (8x50G) speed.
- 800G QSFP-DD DAC Cable: 800G QSFP-DD to 800G QSFP-DD, supports 800G (8x100G) speed.
- 800G OSFP DAC Cable: 800G OSFP to OSFP, supports 800G (8x100G) speed.
- 40G Breakout Cable: 40G QSFP+ to 4x 10G SFP+
- 100G Breakout Cable: 100G QSFP28 to 4x 25G SFP28
- 200G Breakout Cable: 200G QSFP-DD to 2x 100G QSFP28, 200G QSFP56 to 4x 50G SFP56
- 400G Breakout Cable: 400G QSFP-DD to 4x100G QSFP56, 400G QSFP-DD to 2x200G QSFP56
- 800G Breakout Cable: 800G OSFP to 2x400G OSFP
| Part # | Product Description | Data Rate | Wavelength | Distance |
| SFP-1G-DAC1M | SFP DAC | 1G | Passive | 1M |
| SFP-1G-DAC2M | SFP DAC | 1G | Passive | 2M |
| SFP-1G-DAC3M | SFP DAC | 1G | Passive | 3M |
| SFP-1G-DAC5M | SFP DAC | 1G | Passive | 5M |
| SFP-1G-DAC7M | SFP DAC | 1G | Passive | 7M |
| SFP-1G-ACC10M | SFP DAC | 1G | Active | 10M |
| SFP-1G-ACC12M | SFP DAC | 1G | Active | 12M |
| SFP-1G-ACC15M | SFP DAC | 1G | Active | 15M |
| SFP-10G-DAC1M | SFP+ DAC | 10G | Passive | 1M |
| SFP-10G-DAC2M | SFP+ DAC | 10G | Passive | 2M |
| SFP-10G-DAC3M | SFP+ DAC | 10G | Passive | 3M |
| SFP-10G-DAC5M | SFP+ DAC | 10G | Passive | 5M |
| SFP-10G-DAC7M | SFP+ DAC | 10G | Passive | 7M |
| SFP-10G-ACC10M | SFP+ DAC | 10G | Active | 10M |
| SFP-10G-ACC12M | SFP+ DAC | 10G | Active | 12M |
| SFP-10G-ACC15M | SFP+ DAC | 10G | Active | 15M |
| SFP-25G-DAC1M | SFP28 DAC | 25G | Passive | 1M |
| SFP-25G-DAC2M | SFP28 DAC | 25G | Passive | 2M |
| SFP-25G-DAC3M | SFP28 DAC | 25G | Passive | 3M |
| SFP-25G-DAC5M | SFP28 DAC | 25G | Passive | 5M |
| QSFP-40G-DAC1M | QSFP DAC | 40G | Passive | 1M |
| QSFP-40G-DAC2M | QSFP DAC | 40G | Passive | 2M |
| QSFP-40G-DAC3M | QSFP DAC | 40G | Passive | 3M |
| QSFP-40G-DAC5M | QSFP DAC | 40G | Passive | 5M |
| QSFP-56G-DAC1M | QSFP DAC | 56G | Passive | 1M |
| QSFP-56G-DAC2M | QSFP DAC | 56G | Passive | 2M |
| QSFP-56G-DAC3M | QSFP DAC | 56G | Passive | 3M |
| QSFP-56G-DAC5M | QSFP DAC | 56G | Passive | 5M |
| QSFP-100G-DAC1M | QSFP DAC | 100G | Passive | 1M |
| QSFP-100G-DAC2M | QSFP DAC | 100G | Passive | 2M |
| QSFP-100G-DAC3M | QSFP DAC | 100G | Passive | 3M |
| QSFP-100G-DAC5M | QSFP DAC | 100G | Passive | 5M |
| Q56-200G-DAC1M | QSFP56 DAC | 200G | Passive | 1M |
| Q56-200G-DAC2M | QSFP56 DAC | 200G | Passive | 2M |
| Q56-200G-DAC3M | QSFP56 DAC | 200G | Passive | 3M |
| QDD-400G-DAC1M | QSFP-DD DAC | 400G | Passive | 1M |
| QDD-400G-DAC2M | QSFP-DD DAC | 400G | Passive | 2M |
| QDD-400G-DAC3M | QSFP-DD DAC | 400G | Passive | 3M |
| Q-4S-DAC1M | QSFP+ to 4x SFP+ Breakout | 40G | Passive | 1M |
| Q-4S-DAC2M | QSFP+ to 4x SFP+ Breakout | 40G | Passive | 2M |
| Q-4S-DAC3M | QSFP+ to 4x SFP+ Breakout | 40G | Passive | 3M |
| Q-4S-DAC5M | QSFP+ to 4x SFP+ Breakout | 40G | Passive | 5M |
| Q-4S-DAC7M | QSFP+ to 4x SFP+ Breakout | 40G | Passive | 7M |
| Q-4S28-DAC1M | QSFP+ to 4x SFP+ Breakout | 100G | Passive | 1M |
| Q-4S28-DAC2M | QSFP28 to 4x SFP28 Breakout | 100G | Passive | 2M |
| Q-4S28-DAC3M | QSFP28 to 4x SFP28 Breakout | 100G | Passive | 3M |
| Q-4S28-DAC5M | QSFP28 to 4x SFP28 Breakout | 100G | Passive | 5M |
| Q-4S28-DAC7M | QSFP28 to 4x SFP28 Breakout | 100G | Passive | 7M |
| QDD-2Q56-DAC05M | 400G QSFP-DD to 2x 200G QSFP56 Breakout | 400G | Passive | 0.5M |
| QDD-2Q56-DAC1M | 400G QSFP-DD to 2x 200G QSFP56 Breakout | 400G | Passive | 1M |
| QDD-2Q56-DAC2M | 400G QSFP-DD to 2x 200G QSFP56 Breakout | 400G | Passive | 2M |
| QDD-2Q56-DAC2.5M | 400G QSFP-DD to 2x 200G QSFP56 Breakout | 400G | Passive | 3M |
FAQ
Q: Can you provide a compatible DAC cable for cross-brand linking?
A: Sure, we can. We provide customized direct-attach cables with different compatibilities on a cross-brand switch (like Cisco to Juniper), allowing for a perfect link.
Q: What is the maximum length of a DAC cable?
A: It depends on their data rate.
- A passive 10G DAC cable can offer a maximum length of 10 meters (~33 feet), while an active 10G cable can reach 15 meters (~49 feet).
- 40G DAC cable can offer a maximum length of 7 meters (~23 feet).
- 100G DAC cable can offer a maximum length of 5 meters (~16 feet).
- 400G DAC cable can offer a maximum length of 3 meters (~10 feet).
You may consider the AOC cable or optical transceiver for long-distance applications.
Q: What are the disadvantages of a DAC cable?
A: The critical disadvantages of DAC cable include:
- Short length limit (usually 7m for passive cables)
- DAC cables are thicker and less flexible than optical cables, making them difficult to install and route in tight spaces. This can make cable management challenging, especially in crowded environments with limited space.
Final Words
Now, I hope you enjoyed my guide to DAC cables.
Are you clear about their meaning and types?
What types of DACs are used in your switches?
Do you plan to upgrade to 100G or 400G DAC?
Are there any topics missed in this post?
Let me know by Leaving a message now.
Read more:
- What is the difference between DAC and AOC Cables?
- What you need to know about Optcore 400G QSFP-DD DAC Cables
- 10GBASE-T Cabling vs. 10G SFP+ DAC, Which One is Better?
- Passive vs Active DAC cable: How to Choose?
