Dac cable vs sfp+: What's the difference?

The development of artificial intelligence and Internet of things presents new challenges to the expansion of data centers, and there is often a contradiction between technology and cost. In order to realize high density and high capacity, it is important to control cost factors and reasonable wiring. In the wiring, we can choose the high-speed cable and the optical transceiver cables, so how do we choose these two products in the actual scene? What are the differences and what advantages do they have? Let’s study together about the differences between 10G SFP+ DAC and 10G SFP+ transceivers.

As a transmission medium, 10G SFP+ DAC and 10G optical transceivers can be selected. What is the difference between the two?

• The 10G DAC is connected to two switches through copper cables. The SFP+ optical transceiver is connected to the jumpers to connect the two switches.

• 10G DAC is short-distance transmission; the longest distance is 15M, used in the engine room.

• The SFP+ transceivercan perform long-distance transmission. The longest single fiber is 80KM, and the longest dual fiber is 100KM.

DAC (Direct Attach Copper) cables and SFP+ modules are both used in high-speed networking environments, especially in data centers. However, they serve slightly different purposes and have distinct characteristics:

1. Form and Composition:

   • DAC: DAC is a copper cable that comes with SFP+ connectors attached on both ends. It's essentially a fixed length, pre-terminated cable.

   • SFP+: Stands for Small Form-Factor Pluggable. SFP+ is a compact optical transceiver module that interfaces between communication devices (like switches and routers) and the fiber or copper network cables.

2. Medium:

   • DAC: Uses copper as the transmission medium.

   • SFP+: Can be used with either optical fiber or copper, depending on the type of SFP+ module. For optical connections, you'd use an SFP+ transceiver with a separate fiber optic cable. There are also copper-based SFP+ modules that use a separate RJ45 cable.

3. Distance/Reach:

   • DAC: Typically used for short distances, usually up to 7 meters for most applications, though some can go a bit longer.

   • SFP+: Depending on the type, SFP+ transceivers can cover short distances (similar to DAC) when using copper or much longer distances (up to several kilometers) when using optical fiber.

4. Cost:

   • DAC: Generally cheaper than an SFP+ transceiver + fiber cable combination for the same distance.

   • SFP+: Might be more expensive, especially when considering the combined cost of the module and the separate cable.

5. Use Cases:

   • DAC: Often used for interconnecting switches and servers in close proximity within a rack or in adjacent racks in data centers.

   • SFP+: More versatile due to its ability to connect devices over longer distances, especially the fiber versions. Used in both data center interconnects and broader network connections.

6. Flexibility:

   • DAC: Less flexible because it's a fixed-length cable with connectors attached.

   • SFP+: Offers more flexibility. You can select the appropriate transceiver for your needs (short distance, long distance, fiber, copper) and pair it with the appropriate cable.

What is dac cable?

A DAC (Direct Attach Copper) cable is a type of high-speed cable commonly used in data centers to connect devices such as switches, routers, and servers over short distances. Here are some key characteristics and details about DAC cables:

1. Composition: DAC cables consist of shielded copper twinaxial cable with integrated SFP (Small Form-Factor Pluggable) connectors on both ends.

2. Types: There are two main types of DAC cables:

   • Passive DAC: These cables do not have active components and typically operate over shorter distances, often up to 7 meters.

   • Active DAC: These cables have active electronic components to boost the signal and are used for slightly longer distances, typically up to 15 meters.

3. Speeds: DAC cables support various data rates, including 1Gbps, 10Gbps, 25Gbps, 40Gbps, and 100Gbps, depending on the specifications.

4. Advantages:

   • Cost-Effective: For short-distance connections, DAC cables are often cheaper than using optical transceivers with separate fiber optic cables.

   • Low Latency: Copper DAC cables offer very low latency, which is beneficial in environments like high-frequency trading.

   • Ease of Use: They are plug-and-play, making installations simpler compared to separate transceiver and cable setups.

5. Applications: DAC cables are commonly used in data centers for:

   • Interconnecting switches and servers within the same rack or adjacent racks.

   • Connecting network devices in a high-speed network environment over short distances.

6. Limitations:

   • Distance: DAC cables are designed for short distances due to the inherent limitations of signal propagation over copper. As mentioned earlier, most are used for distances up to 7 meters for passive and up to 15 meters for active cables.

   • Flexibility: Since the connectors are integrated into the cable, there's less flexibility in terms of length and connector type.

The Advantages of 10G SFP+ DAC:

The 10G DAC is a copper cable designed with SFP+ connectors on both ends and is less expensive than a 10G optical transceiver.

The use of 10G DAC wiring is more flexible, transmission distance up to 15 meters, in the actual construction process is less difficult to operate.

10G DAC cabling saves on connected devices, eliminating the need for patch panels, and servers and network equipment can be directly connected to TOR switches, which indirectly save on input costs.

In conclusion, while both DAC and SFP+ are utilized in high-speed network connections, the choice between them largely depends on the specific requirements of the application, including distance, cost, and flexibility considerations.

Despite these limitations, DAC cables are highly favored in data center environments because of their cost-effectiveness for short-range connections and their ease of use.

What is SFP+ Optical Module？

The SFP+ (Small Form-factor Pluggable Plus) optical module is an enhanced version of the standard SFP module, designed to support data rates up to 10 Gbps (10 Gigabit per second). Like the SFP, the SFP+ is a compact, hot-swappable module that provides a flexible interface solution for both telecommunication and data communication applications.

Here are the main features and details about the SFP+ optical module:

1. Data Rate: Designed primarily to support 10 Gbps data rates, making it suitable for 10 Gigabit Ethernet, 8 Gbps Fiber Channel, and other high-speed applications.

2. Hot-swappable: Like the SFP, the SFP+ modules can be inserted or removed from a switch, router, or other network device without needing to power down the device.

3. Variety: Supports various types based on distance, mode, and wavelength:

   • Distance: Ranges from short-reach (several meters) to long-reach (up to 40 kilometers or more, depending on the specific module).

   • Mode: Available for both Single-Mode Fiber (SMF) and Multi-Mode Fiber (MMF).

   • Wavelength: Common wavelengths include 850nm (typically for short distances on MMF), 1310nm, and 1550nm (for longer distances on SMF).

4. Direct Attach Copper (DAC) Cables: SFP+ interfaces are also used with DAC cables, which are copper cables with SFP+ connectors on both ends, suitable for short interconnects within a data center.

5. Active Optical Cable (AOC): This is an integrated cable that embeds active electronics in the connectors to convert the electrical signal to optical and vice versa. AOCs are used for short to medium distances and offer the advantages of optical modules without separate connectors and patch cables.

6. Standardization: Like the SFP, the SFP+ design is governed by a Multi-Source Agreement (MSA), ensuring that modules from different manufacturers can interoperate in equipment from various vendors.

7. Diagnostics: Many SFP+ modules come with digital diagnostic monitoring capabilities, which allow for real-time monitoring of parameters such as temperature, transmitted and received optical power, and supply voltage.

8. Power Consumption: Generally, SFP+ modules consume less power than older 10G modules like the XENPAK, X2, or XFP.

The Advantage of 10G SFP+ Transceivers:

If the vertical distance of the wiring does not exceed the cabinet, 10G DACs can be used for the connection. When the distance between the TOR switch and the network switch is greater than 15M, multimode optical fibers and fiber transceivers can be selected. Usually, OM3/OM4 LC fiber jumpers and 10G SFP+ optical transceivers are used. In other words, 10G SFP+ optical transceivers are widely used in long-distance transmission.

In summary, the SFP optical module provides a flexible and easy-to-use solution for many network connectivity applications, allowing users to select the appropriate transceiver based on distance, mode, and other factors.

In summary, the SFP+ optical module is a compact, flexible, and efficient solution for 10G connectivity in various network environments, from data centers to wide-area networks. As network speeds continue to increase, SFP+ remains a prevalent choice for 10G applications.