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SFP+ DAC Twinax Cable Deployment Considerations

August 25, 2016

Network cabling has gone through profound changes over the years, making a great leap forward to higher-speed fiber cables. But in some cases, copper twinax cable still has an significant role to play. This post will introduce some basic information about SFP+ DAC twinax cable, and considerations for deploying 10G SFP+ DAC cables.

SFP+ DAC Twinax Cable Basics

SFP+ DAC twinax cable is a copper interconnect using a twinax cable assembly that connects directly into the SFP+ housing. By directly connecting two SFP+ slots, it effectively eliminates the cost-prohibitive optical transceiver required in the equipment, and greatly reduces the power consumption, latency and installation time. 10G SFP+ DAC twinax cable with a max length of 10 m is commonly used in intra-rack and inter-rack connections: including interconnection of top-of-rack switches with servers and storage devices within a rack or in adjacent racks.

10g sfp+ copper twinax cable

Figure 1: FS SFP+ DAC cables.

Can I Use SFP+ DAC Twinax Cable in SFP Ports?

Yes, SFP+ cables are backward compatible to SFP ports and will work fine. But SFP cables are not compatible to SFP+ ports. SFP cables can be plugged into SFP+ ports but they are not designed for 10Gb/s data rates.

Can I Use a Compatible SFP+ DAC Twinax Cable on Cisco Switches?

Yes, just like optical transceivers, you should not worry about DAC cable compatibility. All the compatible SFP+ DAC twinax cables are made with the same industry standard as the Cisco cables. A qualified SFP+ DAC copper cable should be tested and be fully recognized by Cisco equipment to ensure proper function. Get a reliable direct attach cable manufacturer to buy SFP+ DAC twinax cable, so your compatible SFP+ DAC cable can perform equally great as the branded one—with significantly reduced cost.

Passive or Active SFP+ DAC Twinax Cable?

Passive SFP+ DAC twinax cable contains no electrical components, thus requires little or no power to operate. SFP+ active copper cable, on the contrary, needs DC power to integrates signal processing circuitry into its built-in connectors, making it more expensive. It is recommended to use passive SFP+ DAC when the distance is no more than 7m. As for link distance greater than 7 m (like ToR to EoR), active DACs would be required.

DAC Cable Max Length?

SFP+ DAC can only provide a maximum distance of 10 meters (about 33 feet) based on active copper cables. If the distance is not a problem, the SFP+ DACs tends to be an optimal option because of lower power consumption and lower latency. Read Guide to 10G DAC & AOC Cables for more information about AOC and DAC cables max length.

How to Deploy SFP+ DAC Twinax Cable in Data Center?

SFP+ DAC twinax cable serves as a preferable option for short-reach, high-speed 10 Gigabit interconnects, which were found in mass adoption in data centers and server rooms. To make your installation smooth and hassle-free, you’d better stick to the following rules:

1. Calculate the Length of SFP+ DAC Twinax Cable Beforehand

Assuming to deploy SFP+ DAC twinax cables within a single 84 in. 45 RU cabinet, conservatively the connection from the top U to the bottom will be 7 ft. (2.1m), and approximately 1.5 ft. (0.45m) for routing the cable to any port on either end. Example cabinet with 2 ToR switches and 20 2U servers with dual SFP+ NICs (Network Interface Cards). Hence, the longest cable required to reach the farthest port is 2.1+2×0.45≈3m. So, what you need is to buy SFP+ twinax copper cable at 3 m.

10g sfp+ copper cable length

Figure 2: 3m SFP+ DAC cable in a cabinet.

2. Never, Ever Exceed Bend Radius of SFP+ DAC Twinax Cable

It is important to maintain proper cable bend radius and to secure strain relief of the cable, to properly handle this, always refer to American wire gauge (AWG)—a standard defines the width of the wire diameter. Standard copper SFP+ DAC teinax cables are offered in different wire AWG, and the bending cables should never exceed their minimum bend radius. The table below indicates the minimum sustained bend radius of different cable sizes.

AWG Cable Size
Sustained Bend Radius
24
1.5 inches (38 mm)
26
1.3 inches (33 mm)
28
1.0 inches (25 mm)
30
0.9 inches (23 mm)

3.Secure Your SFP+ Copper Cable With Management Tools

A cable manager or strain relief bar can facilitate SFP+ DAC twinax cable installation and provide strain relief along the horizontal plane. The strain relief bars also help keep cables routed clear from spaces directly behind server and switch equipment, reducing thermal resistance through the equipment and ensuring effective cooling and airflow. Besides, cable ties should be used to bundle the cables together and tie them to the strain relief bars.

secure sfp+ direct atttach copper cable with management tool

Figure 3: SFP+ DAC cable with FS cable management tools.

What to Notice When Buying a SFP+ DAC Twinax Cable?

A qualified SFP+ twinax copper cable is vital to ensure reliable link performance, helping to improve network uptime. Here are some factors to pay attention to when buying a SFP+ DAC twinax cable.

Branded or Compatible SFP+ DAC Twinax Cable?

As vendor branded SFP+ copper twinax cables are rather cost-prohibitive, users are more inclined to choose compatible SFP+ DAC twinax cable made with the same industry standard, but at only a fraction of the cost. As long as picking a trustworthy vendor, you can expect to get SFP+ twinax copper cable with the same performance as branded ones.

10g sfp+ to sfp+ direct attach cable

Figure 4 : FS SFP+ DAC cables connects different vendors' switches or epuipmennt.

Read Product Details of the SFP+ DAC Twinax Cable

To make the purchase meeting with your specific needs, buyers should be fully aware of the ROHS compliance, storage temperature and MSA compliance features in regard to the SFP+ DAC twinax cables. This is important for the proper running of your network system.

AWG Is Also an Important Factor

Another important factor related to SFP+ DAC copper cables is the AWG. There exist various options of SFP+ DAC twinax cable length and wire gauges, like 24AWG, 28AWG and 30AWG. Always remember a rule when choosing the AWG—the longer the distance, the lower the AWG rating should be. The following diagram shows SFP+ DAC twinax cable lengths and AWG offered by FS.COM.

ID
Length (Meters)
Gauge (AWG)
0.5m (2ft)
30AWG
1m (3ft)
30AWG
1.5m (5ft)
30AWG
2m (7ft)
30AWG
2.5m (8ft)
30AWG
3m (10ft)
30AWG
4m (13ft)
24AWG
5m (16ft)
24AWG
6m (20ft)
24AWG
7m (23ft)
24AWG
6.8k

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