High speed data transmission is the prerequisite for enterprise network deployment. For big data centers, 40G is still the mainstream. For 40G network, 40 gbps transceiver and 40gb ethernet cable are important components, and they can be classified according to transmission distance. For long transmission distance, there are 40G LR4 QSFP+ transceiver and singlemode fiber cable; for short transmission distance, there are 40G SR4 QSFP+ transmission and multimode fiber cable. In addition, for 40G short link, there is QSFP+ DAC cable. Two types of QSFP+ DAC cables are available on the market: 56G QSFP+ DAC vs. 40G QSFP+ DAC, what’s the difference between them? This article will make a comparison.

56G QSFP+ DAC Vs. 40G QSFP+ DAC: Same construction

We know that DAC cable is a kind of high speed passive copper cable with one connector on each end. The connectors are not real optical transceiver modules but in the form of optical transceiver module. DAC twinax cable Therefore, QSFP+ DAC consists of two QSFP+ transceiver style connectors and one twinax copper cable. With the same construction, the operation of 56G QSFP+ DAC and 40G QSFP+ DAC in 40G network deployment is the same, too. Just plug the connector into 40G QSFP+ port on the switch on both sides, and then you can get 40G link. Here is a figure of QSFP+ DAC cable for you.


56G QSFP+ DAC Vs. 40G QSFP+ DAC: Different protocols

As qsfp+ passive copper cable, both 56G QSFP+ DAC and 40G QSFP+ DAC are QSFP MSA compliant. But 40G QSFP+ DAC supports 40G InfiniBand 8x DDR, 4x QDR, 10G/40Gigabit Ethernet, Fibre Channel, while 56G QSFP+ DAC supports 40G InfiniBand 4x FDR, 56Gigabit Ethernet, Fibre Channel. What’s the different between InfiniBand DDR, QDR and FDR? InfiniBand (abbreviated IB) is a computer-networking communications standard used in high-performance computing that features very high throughput and very low latency. It is used for data interconnect both among and within computers. InfiniBand is also used as either a direct or switched interconnect between servers and storage systems, as well as an interconnect between storage systems. And the following figure shows InfiniBand specification. We know that QSFP+ DAC cable uses four channels for data transmission. And for 40G QSFP+ DAC, it supports 40G InfiniBand 8x DDR, 4x QDR, so each channel can achieve 10G data rate; for 56G QSFP+ DAC, it supports 40G InfiniBand 4x FDR, so the maximum data rate of each channel is 14G.

InfiniBand Specification


Characterized by low Insertion loss and power consumption, qsfp+ passive copper cable is a cost-effective option for 40G data transmission over short distance. As for 56G QSFP+ DAC vs. 40G QSFP+ DAC, the only different is that the former can operate high bandwidth than the latter one. Therefore, if your network needs 40G data transmission, then 40G QSFP+ DAC cable; if you need more than 40G bandwidth, then choose 56G QSFP+ DAC.

Things You Must Know About DAC Cable

Fiber optic patch cable, also known as fiber jumper, is a fiber optic cable terminated with fiber optic connectors on both ends. And it is widely used in the connections between network equipment. In recent years, a kind of fiber optic patch cable which can transmit data at a high data rate with low cost is popular with data center users. That’s DAC cable or Direct Attach Cable, and this passage will focus on DAC cable’s overview, type and feature.

Overview of DAC Cable

Direct attach cable is a form of high speed cable with two connectors on either end which are in the form of optical transceiver module, such as SFP+, QSFP+ and so on, but they not real optical transceiver modules. Direct attach cable can support Ethernet, Infiniband, Fibre Channel and other protocols. And it is mainly used for the connection between switches, servers, routers in the interconnection application of racks. As a cost-effective solution in short reach applications, DAC is usually used in equipment distribution area (shown as the figure below).

Application of DAC Cable in Equipment Distribution Areas

Types of DAC Cable

Seen from the material of the cable, DAC can be classified into direct attach copper cable and active optical cable (AOC). Direct attach copper cable can either be passive or active, while AOC cable is always active. The following part will separately give an overview of passive direct attach copper cable, active direct attach cable and active optical cable.

Passive Direct Attach Copper Cable

Shown as the figure below, the connectors of passive direct attach copper cable contain no active components. The passive direct attach copper cable provides a direct electrical connection between corresponding cable ends and it can reach the transmission distance of 7m at a data rate of 10 Gbps or 40 Gbps with low power consumption.

Passive Direct Attach Copper Cable

Active Direct Attach Copper Cable

Compared with passive direct attach copper cable, the connectors of active direct attach copper cable contain active components, such as cable drive, to transmit and receive electric signals. Therefore, the active direct attach copper cable consumes more power. While these active components help to improve signal quality and provide a longer cable distance. For example, the active direct attach copper cable can reach the transmission distance of 15m at a data rate of 10 Gbps or 40 Gbps.

Active Direct Attach Copper Cable

Active Optical Cable

The material of AOC’s cable is fiber optic cable and the connectors of active optical cable contain active components, such as rear stage magnifying glass, laser driver and so on. As a result, the transmission distance of active optical cable is much longer than passive direct attach copper cable and active direct attach copper cable’s. Usually, the active optical cable can transmit signals up to 100m.

Active Optical Cable


From the content above, we can easily find that with different components inside connectors, different types of direct attach cables have different features. This part will give a detailed introduction about direct attach copper cable and active optical cable’s features.

For direct attach copper cable:

It supports higher data rates than traditional copper interfaces from 4 Gbps to 10 Gbps per channel.

It is interchangeable and hot swappable with fiber optical modules.

It is a cost-effective solution over optical transceivers and cables or short reach applications.

It supports multiple protocols, such as Gigabit & 10G Ethernet, 8G FC, FCoE, InfiniBand SDR, DDR & QDR.

For active optical cable:

It is an alternative to optical transceivers which eliminates the separable interface between transceiver module and optical cable.

Needing no equipment upgrades, it has a throughput of up to 40 Gbps with QSFP+; it weighs less than a comparable direct attach copper cable.

It is immune to electromagnetic energy because the optical fiber is a kind of dielectric (not able to conduct electric current).


DAC cable is a cost-effective, proven solution for interconnecting networking applications. It uses the same port as an optical transceiver, but with significant cost savings and power savings advantages in short reach applications. What’s more, the product is continuing to evolve to meet industry needs of higher data rates and densities with low power consumption.

Introduction to Fiber Optic Patch Cable

Fiber optic patch cable is a fiber optic cable terminated with fiber optic connectors on both ends. It has thick layer of protection and is commonly used to connect the optical transmitter, receiver, and the terminal box in fiber optic network. Fiber optic patch cable is also known as fiber optic patch cord, fiber optic jumper.

The fiber optic patch cable is constructed from the core, the cladding, the coating, strengthening fibers and the cable jacket. Transparency of the core permits transmission of optic signals with little loss over great distances; the cladding causes light to be confined to the core of the fiber; the coating’s low refractive index reflects light back into the core, minimizing signal loss; the protective cable jacket minimizes physical damage to the core and coating. And on both end, there are connectors. (shown in the following figure.) For multi-core cable, the core measures 50 um to 65 um in diameter, approximately the thickness of a human hair; while the core of single-core cable is 8 um to 10 um in diameter.

Fiber optic patch cable

Fiber optic patch cable is characterized by:

  • Low insertion loss
  • High return loss
  • Good repeatability
  • Good interchange
  • Excellent environmental adaptability.

There are various types of fiber optic patch cables and they can be classified mainly by the types of cables and connectors.

Fiber Optic Patch Cables with Different Cable Types

Single-mode fiber is generally yellow with a blue connector, and it has a longer transmission distance.

Multimode fiber is generally orange or grey with a cream or black connector, and it has a shorter transmission distance.

Armored fiber optic patch cable uses a layer to protect the fiber inside from being bitten or other damage.

Bend insensitive fiber optic patch cable is widely used in FTTH and it is not sensitive to stress and bending.

Mode conditioning patch cable is a kind of double multimode patch cable and has a small length of single-mode fiber at the beginning of transmission length.

Fiber Optic Patch Cables with Different Connector Types

Fiber optic patch cable can be terminated with various types of connectors, such as LC, SC, ST, FC, MTRJ, E2000, MU and MPO/MTP. In addition, the connectors on both end can be the same or different. Therefore, the following part will focus on different types of connectors.

LC Connector

LC connector has a push and latch structure, with plastic shell and accurate 1.25mm ceramic ferrule. LC connector is in small size and has good performance. It is very popular and widely used for dense installation.

LC connector

SC Connector

SC stands for Subscriber Connector or Square Connector or Standard Connector. It is a kind of push and pull connector. SC connector has a locking tab which can make accurate alignment through ceramic ferrule. It features low cost, simplicity as well as good durability and it’s commonly used in data communication and telecommunication fiber optic market.

SC connectoe

ST Connector

ST stands for Straight-Tip and ST fiber optic cable has a bayonet rotary locking mechanism. There is a 2.5mm diameter ferrule on ST connector, the same as SC connector’s.

ST connectoe

FC Connector

FC connector is a kind of bolt type connector. FC stands for Fixed Connector which has a metal shell and bolt connection structure. The ferrule and sleeve on FC connector are the same with SC connector’s.

FC connector

MT-RJ Connector

MT-RJ connector which is developed from MT and RJ connectors. MT-RJ stands for Mechanical Transfer Registered Jack. There are plastic cover and ferrule on MT-RJ connector and it is characterized by the connection with two fibers, that is, two fibers are connected in one MT-RJ connector. MT-RJ connector has female type and male type. The difference between these two types is that the male type is constructed with two ferrules on one connector.

MT-RJ connector

E2000 Connector

E2000 connector has a spring-compressed valve and push-pull locking device to protect ferule from dust and wear. When inserting the connector, push-pull locking device will fully lock; when pulling it out, the spring-compressed valve will close automatically.

E2000 connector

MU Connector

MU connector has a plastic shell and push-pull locking mechanism. MU connector is small in size and has a ferrule with 1.25mm diameter. And MU connector is used in advanced optical transmission and exchange, user system or high speed data application.

MU connector

MPO/MTP Connector

MPO connector is high-density fiber optic connector and uses precise modeled MT ferrule. In single MPO patch cable, there are several fiber counts, such as 12 fibers, 24 fibers and 36 fibers. MTP is the optimized version of MPO. MTP adopts push-pull locking mechanism and it’s easy to insert and pull out.

MTP connector

Fiber optic patch cables are widely used in various fields, such as the connections to CATV (Cable Television), telecommunication networks, computer fiber networks and fiber test equipment. Applications include communication rooms, FTTH (Fiber to The Home), LAN (Local Area Network), FOS (fiber optic sensor), Fiber Optic Communication System, Optical fiber connected and transmitted equipment, Defense combat readiness, etc.