Direct Attach Cables

Direct Attach Cable (DAC): three important things you should know

DAC (Direct Attach Cable) is usually a cable assembly purchased with fixed length and fixed connectors at both ends. The port cannot be replaced, and the module head and copper cable cannot be separated. The DAC high-speed cable has been accepted and used by more and more users with the significant advantages of high-cost performance, high efficiency, high rate, high recombination and low loss.

1. The introduction of common types of Direct Attach Cables (DAC)

· 10G SFP+ DAC

The 10G SFP+ DAC is a copper cable with SFP+ connectors at both ends. It has high wiring flexibility and transmission distance of up to 15m. And it with low operational difficulty in the actual construction process. The 10G SFP+ DAC cabling can save connection equipment without using distribution frames. Servers and network equipment can be directly connected to tor switches. It has the advantages of low power consumption, low cost and low delay.

· 25G SFP28 DAC

There are two types of 25G SFP28 DAC：

The 25G SFP28 to SFP28 DAC is a very cost-effective solution for short-distance link transmission, which can establish the 25G link through the SFP28 port of the switch, complying with IEEE P802.3BY and SFF-8402 SFP28 standards, and is widely used in data center or super-computing center system scenarios.

The 100G QSFP28 to 4 x SFP28 DAC is suitable for stacking and clustering between short-range big data devices, with 100G QSFP28 interface at one end and four 25G SFP28 interfaces at the other end, providing customers with 100G data transmission, in compliance with IEEE 802.3BA standard, SFF-8665/SFF-8679, IEEE 802.3BJ and Infiniband EDR standards.

The 25G SFP28 DAC direct attach cable is widely used in the data center because its data transmission can not only improve the network performance of the data center but also effectively reduce the number of top-of-rack switches deployed in the data center, which can fully meet the high-speed and high-density requirements of the data center for network deployment. In addition, the 10G optical modules can not meet most of the data center rate requirements of the current situation, the 40G and 100G products are relatively high price and power consumption while the 25G SFP28 DAC direct attach cable can just meet the requirements of low power consumption and low cost of data centers.

· 40G QSFP+ DAC

There are two types of QSFP 40G DAC:

The 40G QSFP+ to QSFP+ DAC is connected with QSFP+ connectors on both ends and is suitable for connecting two 40G network devices with a maximum transmission distance of 7m. The transmission distance of passive fiber is generally less than 7m, while the transmission distance of active fiber is longer, depending on the manufacturer.

The 40G QSFP+ to 4 x SFP+ DAC is connected with QSFP+ connectors at one end and four 10G SFP+ connectors at the other end, which are used to connect 40G devices and 10G devices, suitable for 10G and 40G network connection, with a maximum transmission distance of 7m.

· 100G QSFP28 DAC

The 100G DAC has 100G QSFP28 DAC direct attach cable and 100G QSFP28 to 25G SFP28 DAC two types:

The 100G QSFP28 to QSFP28 DAC Direct Attach Cables: both ends are 100G interfaces, which are suitable for stacking and direct connection between 100G devices in a short distance, and are used in the same rack.

100G QSFP28 to 4 x 25G SFP28 DAC Direct Attach Cables: for interconnection between 100G and 25G devices where one end is a 100G interface and the other end is four 25G interfaces, supporting a distance range of 1m - 5m.

The 100G QSFP28 DAC high-speed cable provided by Fiber Mall can fully meet users' needs for 100G network construction.

· 200G QSFP56 DAC

The 200G DAC has two packages: QSFP-DD DAC and QSFP56 DAC, both with a wavelength of 850nm. Different from 200G AOC, the power consumption of DAC is very small and can even be ignored, but its farthest transmission distance is only 5m.

The 200G QSFP56 to 2 x 100G QSFP28 DAC: one 200G QSFP56 optical module is connected at one end and two 100G QSFP28 optical modules are connected at the other end, with a transmission distance of 3 meters and a maximum transmission rate of 212.5Gbps. This cabling method is mainly used in 200G to 2x100G networks in the same rack in data centers.

The 200G QSFP56 to 4 x 50G SFP56 DAC: One 200G QSFP56 optical module is connected at one end and four SFP56 optical modules are connected at the other end, with a transmission distance of 3 meters. This 200G QSFP56 to 4 x 50G SFP56 cabling method is mainly applied to 200G to 4x50G devices on the same rack.

· 400G QSFP-DD DAC

Among all types of DAC direct attach cables, the QSFP series (including QSFP+, QSFP28, QSFP56, QSFP-DD) is 4-channel data transmission with larger data capacity (40G-400G) compared to the single-channel SFP series (including SFP+, SFP28, SFP56).

The 400G QSFP-DD DAC has data rates up to 425Gbps with 8-channel 53Gb/s PAM4 modulation and meets the requirements of 400G Ethernet and InfiniBand EDR. Available in a variety of wire gauges from 28AWG to 30AWG. With lengths from 0.5 to 2.5 meters, low insertion loss and low crosstalk, the 400G QSFP-DD DAC is ideally suited for today's ultra-high data transfer data center applications such as servers, routers, switches and data storage.

There are three types of 400G DAC：

1) 400G QSFP-DD to QSFP-DD DAC

2) 400G QSFP-DD to 2 x 200G QSFP56 DAC

3) 400G QSFP-DD to 8 x 50G SFP56 DAC

2. The advantages and disadvantages of Direct Attach Cables (DAC)

· Advantages of Direct Attach Copper Cable

More Cost-effective— Generally speaking, the price of copper cables is much lower than that of optical fibers. The cost of passive copper cables is 2 to 5 times cheaper than fiber cables of the same length. Therefore, the use of high-speed cables will also reduce the cabling costs of the entire data center.

Lower Power Consumption— High-speed DAC (direct attach cable) consumes less power(the power consumption is almost zero) since passive cables do not require a power supply. The power consumption of active copper cables is generally around 440mW. If you use direct attach copper cables instead of AOC fiber cables, you can save hundreds of thousands of kilowatts of electrical power.

Durable–It is designed with a seamless connection form of optical module and optical cable, which reduces the cost and ensures that the optical port is not exposed to dust and other pollutants. Therefore, DAC is less susceptible to damage.

· Disadvantages of Direct Attach Copper Cable

One of the disadvantages of DAC cable is that it is heavier and bulkier than AOC. In addition, it is more susceptible to the effect of electromagnetic interference and attenuation over longer distances due to the electrical signals transmitted between both ends. 

3. The applications of Direct Attach Cables (DAC)

DAC is the best solution to achieve short-distance transmission because of its cheap price and fast transmission speed. It has become the first choice for high-speed data communication solutions. It is widely used in storage area networks, data centers and high-performance computer connections. The direct attach cable has become the preferred solution for users in short-distance application scenarios. It is widely used in data centers interconnection scenarios such as SATA storage devices, RADI system scenarios, core routers, 10G or 40G Ethernet, etc. In the data center, copper cable is generally used to connect servers and storage area networks, and the most commonly used is Direct Attached Copper Cable.