Introduction to DAC Cables

DAC cables, or “Direct Attach Cables", are a kind of optical transceiver assembly widely applied in storage area network, data center, and high-performance computing connectivity etc. They are a form of shielded high speed cable with SFP connectors on either end. They can be used to connect switches to routers and/or servers.

 

Before you purchase this product, a few things you need to know. Firstly, there are different versions of DAC cables. Generally Twinax cables less than 5 meters in length are passive and greater than 5 meters in length are active. The most common version is the “Passive Assembly” where the data cables are directly connected to the transmitting and receiving signal. Because this signal is not very strong, you can reach up to 5 meters with this setup depending on the switch or router. Another version is the active cable version that contains more sophisticated electronics where the transmitting power is amplified to give a better data-pulse. The third version is the “Active Optical Cable". Instead of using a high speed copper wire, this cable uses a hardened glass fiber for transmission. These glass fiber cables are becoming more widely used because of the issues associated with lower-end cables. The main issues are with the coding, if each end has to be connected to a different brand of router or switch, this can cause issues with compatibility. Another common issue is where the switch or router does not give enough power for a (long) passive cable. In this case, there are a lot of CRC errors or packet loss and unstable links—this can be solved by switching to active or active optical cables.

And there are different types of DAC connectors on the market. QSFP+ cables and SFP+ DAC cables are the two main connectors.  supplies various kinds of high speed interconnect DAC cable assemblies including 10G SFP+ cables, 40G QSFP+ cables, and 120G CXP cables. The SFP+ DAC cables provide high performance in 10 Gigabit Ethernet (10GbE) network applications, using an enhanced SFP+ connector to send 10Gbps data through one paired transmitters and receivers over a thin twinax cable. SFP+ DAC cables have a fixed-length cable, typically 1 to 7 m (passive cables) or up to 15 m (active cables) in length, and, like 10GBASE-CX4, are low-power, low-cost and low-latency with the added advantages of using less bulky cables and of having the small form factor of SFP+. SFP+ DAC cables today is tremendously popular, with more ports installed than 10GBASE-SR. QSFP+ (Quad Small Form-factor Pluggable) DAC cables are designed for high-density applications that integrate 4 InfiniBand channels at 10 Gbps per lane. These cables are used for 40 GbE and InfiniBand standards to maximize performance. Recently DAC cables are becoming increasingly popular in the network industry, mainly because the price difference is so large when compared with regular optics. Another reason is that RJ-45 10G is not widely adopted, and most high density 10G switches are delivered with 48x SFP+ ports in 1 Rack Unit.