What is a Direct Attach Copper (DAC) Cable and Its Common Types?

Higher Ethernet speed, cloud computing, IoT, and virtual data centers demand more on operators of data centers. However, DAC cable still maintains its market position not just within data centers but within wider areas of the industry due to its cost efficiency and high performance for data center interconnection. This passage tends to introduce the common DAC cables and their applications for high-density high-speed gigabit ethernet interconnects in data centers. 

 

What is a Direct Attach Cable(DAC)?

DAC is an acronym for Direct Attach Cable, which is generally called direct cable, direct copper cable, or high-speed cable. High-speed cable is a kind of low-cost short-distance connection solution to replace optical modules. Both of its ends have cable assemblies of a module, which are connected to fixed ports only. Besides, the module head and copper can not be separated. However, compared with active optical cables, the connector modules on high-speed cables require no expensive optical lasers and other electronic components. Therefore, both cost and power consumption are saved for short-distance connections.

 

Is DAC Copper or Fiber?

DAC cables are made from shielded Twinax copper coaxial and are factory equipped with modules on either end connected to fixed ports. The modules cannot be removed from the cable. Therefore, all DAC cables are produced at a fixed length. The high-speed copper cable has excellent attenuation performance, low latency, and anti-interference in high-frequency broadband transmission.

 

What is Twinax Cable Used For?

Direct attached Twinax cable can be widely used in data center interconnection such as SATA storage devices, RADI systems, core routers, core switches, servers for 10G/40G/100G Ethernet, and InfiniBand. Generally speaking, this direct attach copper cable provides a cost-effective and high-performance solution for the following situations:

• Top of Rack(ToR)/Adjacent Rack – Either passive or active DAC cable is perfect for shorter ToR or rack-to-rack operations with cost-effective budgets.

• Middle of Row – Active DACs may be a better solution in this application, as long as the transmission distance is less than 15m.

• End of Row – DAC cables are ideal for the end of row architectures as long as the distance is within the 15 meters limit.

 

What Is The Difference Between Active And Passive DAC Cables?

The main difference between an active DAC cable and a passive DAC cable is whether the signal processing is done or not. If there is an electrical component for signal conditioning in the cable, it is an “Active DAC”. If not, it is a “Passive DAC”, since it does not apply electronics for signal conditioning. Apart from the inner component, active and passive DAC cables also differ from each other in link length. A passive DAC Twinax cable transmits an Ethernet signal over a short length (0.5 m-5 m), while an active DAC Twinax cable supports a transmission distance of 5 m-10 m for an Ethernet signal. 

 

9 Most Common DAC Cables

1. 10G SFP+ to SFP+ DAC

10G SFP + to SFP+ DAC adopts passive dual-axis cable assemblies and is directly connected to the SFP + module. It has the characteristics of high density, low power, low cost, and low delay.

What are the types of 10G SFP + to SFP + high-speed cables? Generally speaking, there are three different 10G + to SFP + high-speed twisted pair cables, i.e. 10G SFP + passive copper core high-speed cable (DAC), 10G SFP + active copper core high-speed cable (ACC), 10G SFP + active optical cable (AOC). They are suitable for Ethernet network connectivity within the rack and between adjacent racks, which can save costs significantly.

 

 

10G SFP+ passive copper direct attach cable provides a direct electrical connection interface between the two ends of the corresponding cable, and the transmission distance can reach 12m. However, due to the heavy weight of the cable and considering the signal integrity, the length of the cable is generally limited for the connection within the range of 7m to 10m.

 

SFP 10G Direct Attach Copper Passive Cable 1m-FiberMall 

2. 10G XFP to SFP+ DAC

10G XFP to SFP+ DAC is a twin-ax direct attach copper cable assembly with a 10G XFP interface on one end and a 10G SFP+ interface on the other. Since the XFP optical module does not have the standard DAC copper cable, the signal compensation transmitted by the equipment is low, and the loss of the cable itself is large. Thus it can only transmit over a short distance, generally within 5m, to realize the data connectivity between 10G SFP+ interface and 10G XFP port.

Product Details

FiberMall P/N	XFP-SFP-10G-PC5M	Vendor Name	FIBER MALL
Connector	XFP to SFP+	Max Data Rate	10Gbps
Cable Length	5m (16.4ft)	AWG	AWG 24
Jacket Material	PVC (OFNR)	Minimum Bend Radius	31.5mm
Operation Temperature	0~ 70 °C (32 to 158°F)	Protocols	1x InfiniBand QDR, DDR, SDR, 10G Ethernet, Fibre Channel

 

FiberMall 10G XFP to SFP+ DAC Passive Copper Cable 2m

3. 40G QSFP+ to QSFP+ DAC

40g QSFP + to QSFP + DAC is a high-speed direct attach copper cable consisting of two 40G QSFP+ fiber transceivers and copper core, used for interconnection between 40G QSFP+ ports to 40G QSFP+ port with a transmission distance less than 7m.

 

 

40G QSFP+ to QSFP+ Direct Attach Cable provides a cost-effective way to establish a 40G connection between internal racks and cross-rack with QSFP+ switching ports, which increases the Ethernet network interconnection between the access layer uplink and the trunk link up to 40G / 100G. With its high speed and low latency, it is widely connected to high-speed backbone networks, enterprise network switching, and network storage. 40G QSFP + to QSFP + DAC is one of the most applied types among the portfolio of 40G DAC.

FiberMall QSFP Cable-40G QSFP+ to QSFP+ DAC Passive 4m

4.  40G QSFP+ to 4×SFP+ DAC

40G QSFP+ to 4×SFP+ DAC consists of one 40G QSFP+ fiber transceiver, copper core, and four 10G SFP+ fiber transceiver. One of its ends has the 40G QSFP+ port conforming to SFF-8436 requirements. The other end has four 10G SFP+ ports conforming to SFF-8432 requirements. It connects 40G and 10G equipment (NIC/HBA/CAN, switch, and server) within 7m according to the client’s requirement for the cable length. At present, it is the best option for the exchange of switch ports in an economical and simple way.

 

 FiberMall 40G QSFP+ to 4×SFP+ Direct Attach Copper Cable  

5. 40GQSFP+ to 4 XFP DAC

40G QSFP+ to 4 XFP direct attach copper cable assemblies consists of one 40G QSFP+ fiber transceiver, copper core, and four 10G XFP fiber transceivers. As the XFP fiber transceiver has no DAC copper standard, has low signal compensation provided by a device and the loss of the cable is heavy, it is only used for data transfer within a short distance of 2m and interconnection between the available 40G QSFP+ port and four XFP ports.

 

FiberMall 40G QSFP+ to 4 XFP DAC Twinax Cable

6. 25G SFP28 to SFP28 DAC 

 25G SFP28 to SFP28 DAC can provide customers with 25G high bandwidth Ethernet network interconnection capability. Conforming to IEEE p802.3by Ethernet standard and sff-8402 SFP28, it is widely used in data center or Super-computing Center system scenarios.

FiberMall 25G SFP28 to SFP28 Direct Attach Cable 

 

7.100G QSFP28 to QSFP28 DAC

100G QSFP28 to QSFP28 DAC provides data interconnection through 100G bandwidth and 4x duplex channels. Compliant with SFF-8436 Standard, every channel supports 25Gb/s rate and 100 Gb/s of bandwidth aggregation and is applied for Ethernet network connection between equipment with QSFP28 ports.

 

 

8. 100G QSFP28 to 4×SFP28 DAC

One end of 100G QSFP28 to 4×SFP28 DAC has a 100G QSFP28 port, and the other end has four 25G SFP28 ports. Compliant with SFF-8665/SFF-8679、IEEE 802.3bj and Infiniband EDR Standard, it provides data interconnection through 100G bandwidth and is widely applied for system scenarios at data centers or HPC centers.

 

FiberMall 100G QSFP28 to 4×SFP28 Passive 3m Twinax Network DAC Cable

9. 56G QSFP+ to QSFP+ DAC

The 56G QSFP+ to QSFP+ DAC is an inexpensive copper twin-ax cable with QSFP+ connectors on both sides and provides 56 Gigabit Ethernet connectivity between devices with QSFP+ ports. This direct attach high-speed cable is perfect for very short distances and offers a highly cost-effective way to establish a 56 Gigabit connectivity. In compliance with InfiniBand FDR and QSFP+ Multi-Source Agreement (MSA) standards SFF-8436, it is designed for 56G (14Gx4) interconnecting networking applications such as high-performance computing (HPC), enterprise networking including top-of-rack switching, and network storage markets.

 

 

FiberMall 56G QSFP+ to QSFP+ Copper Direct Attach Cable 1m (3ft)

How Long Can DAC Cables Be? 

Cable Types	Model	Length	Connector
SFP+ to SFP+ DAC	SFP-10G-PC1M	1M	SFP+
	SFP-10G-PC3M	3M	SFP+
	SFP-10G-PC5M	5M	SFP+
	SFP-10G-AC7M	7M	SFP+
	SFP-10G-AC10M	10M	SFP+
QSFP+ to QSFP+ DAC	QSFP-40G-PC1M	1M	QSFP+
	QSFP-40G-PC3M	3M	QSFP+
	QSFP-40G-PC5M	5M	QSFP+
QSFP+ to 4*SFP+ DAC	QSFP-4SFP-PC1M	1M	QSFP+ to 4*SFP
	QSFP-4SFP-PC3M	3M	QSFP+ to 4*SFP
	QSFP-4SFP-PC5M	5M	QSFP+ to 4*SFP
QSFP28 to QSFP28 DAC	QSFP28-100G-PC1M	1M	QSFP28
	QSFP28-100G-PC3M	3M	QSFP28
	QSFP28-100G-PC5M	5M	QSFP28
SFP28 to SFP28 DAC	SFP28-25G-PC1M	1M	SFP28
	SFP28-25G-PC3M	3M	SFP28
	SFP28-25G-PC5M	5M	SFP28
	SFP28-25G-AC10M	10M	SFP28
QSFP28 to 4*SFP28 DAC	QSFP28-4SFP28-PC1M	1M	QSFP28 to 4*SFP28
	QSFP28-4SFP28-PC3M	3M	QSFP28 to 4*SFP28
	QSFP28-4SFP28-PC5M	5M	QSFP28 to 4*SFP28

 

Why Choose DAC Cables Over Optical Transceivers?

1. High performance: DAC is suitable for short-distance wiring of the data center with its strong exchangeability of integration scheme;

2. Energy saving and environmental protection: The internal material of the high-speed cable is copper, which has a good natural heat dissipation effect and the qualities of energy-saving and environmental protection;

3. Low power consumption: Since the passive cable does not need power, the power consumption is almost 0.

4. Low cost: Copper cables are much cheaper than fiber, so using high-speed cables can greatly reduce the wiring costs of the entire data center.

 

In conclusion

In the era of the rapid development of data centers and connection data, DAC greatly expands its market and has gained a large share of the IDC market.  As data speed is getting close to 400G at data centers, DAC high-speed cable products are applied by more and more clients as it has the qualities of cost-effectiveness, high rates, and low loss. At the same time, quite a lot of high-speed data centers also prefer DAC products when considering communications solutions.