10G SFP+ DAC Cable - 10GSFP+Cu

Over the years, 10GbE has successfully stretch its reach from enterprise data centers to midmarket networks due to the increased bandwidth requirements and the growth of enterprise applications. Price, performance and flexibility have made 10 GbE an attractive choice. Meanwhile, due to the escalating deployments of multi-core processor-based servers, customers require flexible and scalable I/O solutions to meet the requirements. Consequently, 10GSFP+Cu that meets the above requirements has become very popular.

Basics of 10GSFP+Cu

Definition

10GSFP+Cu is also known as 10GBASE-CR, 10GBASE-CX1 and 10G SFP+ direct attach copper. 10GSFP+Cu is a copper interconnect using an inexpensive twinax copper cable assembly with SFP+ connectors on both sides based on SFP+ MSA (multi-source agreement). This standard has a transmission range of 10 m, and similar to 10GBASE-CX4, it has the advantage of low power, low cost and low latency. In addition, unlike 10GBASE-CX4, this standard has the added advantage of using less bulky cables and having the small form factor of SFP+.

Types

SFP+ Direct Attach uses a copper 10GbE cable that comes as active or passive twinax cable assembly and connects directly into an SFP+ housing. 10G SFP+ active copper cable assemblies have a silicon chip to boost the performance of the cable. Without a chip, the cable is considered a “passive” cable. This active boosting allows cables to be more compact, thinner, longer, and transmits data faster than their passive equivalents. Passive copper cables are more susceptible to degradation due to attenuation and crosstalk. The benefit of embedding chip technology in cables is a reduction in the copper used in cable production, reducing the overall form factor and weight of the cable. Other benefits include longer reach and lower power consumption. Generally, SFP+ Direct Attach has a fixed-length cable. Twinax cables shorter than 7 meters are passive and those longer than 7 meters are active.

Learn more about: Data Center Cabling Solution: DAC Cables vs AOC Cables

This cost-effective technology solution for replacing 10G optical modules is useful for interconnecting a stack of top-of-rack switches and short-distance connections between switch ports and Ethernet interfaces on servers and storage devices in a rack. By incorporating SFP+ DACs into the physical infrastructure, organizations can achieve 10G performance without additional signal processing or conversion. This provides an ideal low power and low latency 10 Gbps server interconnect option for ToR switching deployments.

10GSFP+Cu Link

The 10GSFP+Cu link utilizes a receive equalizer in the host port physical layer PHY/SerDes in order to compensate for the Inter Symbol Interference (ISI) introduced by the cable. Electrical and mechanical specifications for SFP+ optical modules, 10G SFP+ DAC and hosts are defined in the SFF-8431 specification developed by the SFF Committee, with broad industry participation. 10GSFP+Cu interoperability test can conduct with each host PHY or network interface card (NIC), which can demonstrate the 10GSFP+Cu specification’s consistency and host interoperability over various cable lengths, host channels and PHYs.

10GSFP+CU Signaling Components

The direct attach twinax cables use the SFP+ connector module that is used on 10 Gbps optical fiber links. An SFP+ port may support either active or passive DAC cables or both. There is no standard for this cable type, so you cannot assume that a direct attach port can support either cable type. The DAC cables and their SFP+ connector modules use an electrical signaling interface called SFI, which is defined as the “SFP+ high-speed serial electrical interface”. The SFI definition enables 10 Gbps operation over a single differential signaling path in each direction for a total of two pairs or four-wire connections. The twinaxial cable includes the two pairs of signal-carrying wires in a coaxial cable format, providing high performance and stable signaling over the length of the cable.

10GSFP+CU Signal Encoding

The SFP+ MSA specifications for DAC cables note that 10GSFP+Cu connections can only be used on systems with common power grounds. The power supplies for the switches or any computers are connected to them over DAC cables. They must be connected to the same local power grid with the common ground between all devices. Otherwise, it may result in electrical damage to the interfaces or the devices.

10GSFP+Cu VS. 10GBASE-T

10GBASE-T is an IEEE 802.3an standard that supports the creation of technology that is capable of transmitting 10 Gigabit Ethernet up to 100 meters over unshielded or shielded twisted-pair cables. Prior to the development of 10GBASE-T, SFP+ Direct Attach Copper is a low-cost alternative to traditional fiber and twisted-pair copper cabling in data center deployments for 10 Gbps connection. SFP+ DAC provides better cable management for high-density deployments and enhanced electrical characteristics for the most reliable signal transmission.

Here, we have summarized the advantages of 10GSFP+Cu over 10GBASE-T as follows:

• The connection of 10G SFP+ DAC cable is able to transmit at 10 Gigabits/second full-duplex speed over 5-meter distances.

• 10G SFP+ DAC cable offers 15 to 25 times lower transceiver latency than current 10GBASE-T Cat 6/Cat 6a/Cat 7 cabling systems: 0.1μs for twinax with SFP+ versus 1.5 to 2.5μs for current 10GBASE-T specification.

• The power draw of twinax with SFP+ is around 0.1 watts, which is also much better than 4-8 watts for 10GBASE-T.

• Twinax copper cabling has BER better than 10-18.

Therefore is acceptable for applications in critical environments. Learn more about 10GBASE-T vs SFP+ vs DAC: Which to Choose for 10GbE Data Center Cabling?

10GSFP+Cu Deployment Considerations

1. Don’t Exceed Bend Radius of Your SFP+ DAC Cables

It is important to observe and maintain proper cable bend radius and provide adequate and secure strain relief on the cable. In order to help maintain proper bend radius, it is recommended to confirm the American wire gauge (AWG) of your SFP+ DAC cables first. SFP+ direct attach copper cables are offered in different wire AWG depending on length. Cables must not be bent below their minimum bend radius, which depends upon cable size as expressed in AWG. The table below summarizes minimum values typically admitted for SFP+ DAC cables sustained bend radiuses.

2. Calculate the Length of Your SFP+ DAC Cables

When you deploy SFP+ cables within a single 84 inches 45 RU cabinet, conservatively the longest connection will be 7 ft. or 2.1m to reach from the top U to the bottom and approximately 1.5 ft. or 0.45m to route to any port on either end. Example cabinet with 2 top of rack switches and 20 2U servers with dual SFP+ NICs (Network Interface Cards) total of 40 SFP+ cables. Conservatively, longest cable required to reach farthest port is 2.1+2×0.45≈3m. A 3m cable should be adequate to connect any two ports within a cabinet.

3. Use Cable Management Tools to Bear Your Heavy SFP+ DAC Cables

To help manage the weight of bundled cables and ensure they do not sag over time, a strain relief bar should be installed to support SFP+ DAC cables and provide strain relief along the horizontal plane. Strain relief bars facilitate the correct alignment of cable and connector into the port, and help installers observe manufacturer and bend radius requirements of cable close to the connector. The strain relief bars also keep cables routed clear from spaces directly behind server and switch equipment, reducing thermal resistance through the equipment and promote effective cooling and airflow. Besides, cable ties should be used to bundle the cables together and tie them to the strain relief bars and cable managers. This should be done carefully to ensure the cables are firmly in place and will not move, but not so tight as to deform or stress the cable jacketing.

Conclusion

Until now, media systems have been evolving to carry 40 and 100 Gb/s Ethernet signals over short-range copper coaxial cables. As you can see, the Ethernet system has been reinvented to provide more flexible and reliable cabling, to accommodate the rapid increase in network traffic with higher speeds, and to provide more capabilities for today’s more complex network systems. Also, direct attach copper will continue to play an important role in the telecommunication industry.