IDC Spine-Leaf Cabling Solution Guide: Transceivers vs DAC Cables vs AOC Cables

Spine-Leaf network architecture is a new data center topology architecture. Different from traditional 3-layer architecture, Spine-Leaf architecture consists of two layers, a spine and a leaf. The mainstream network cabling solution includes direct attach cable (DAC), active optical cable (AOC), and optical transceiver + fiber optic cable. It is important to choose a suitable cabling system for the network architecture. This article will tell which solution is suitable for specific parts of Spine-Leaf architecture.

Why is Spine-Leaf Network Architecture Important?

Traditional switch network architecture of data centers adopts three-layer network architecture, that is core-aggregation-access, as shown in figure 1. Based on traditional 3-layer architecture, communication between two access switches may need three switches of the aggregation-core-aggregation layer, which is not suitable for large-scale virtual data centers. 

The data stream data center disposed of is larger and larger, which requires lower latency, higher bandwidth, faster deployment, and higher scalability for network systems. So here comes the Spine-Leaf network architecture, which is the first choice of Internet Data Center construction. Different from the traditional 3-layer, the Spine-Leaf network architecture adopts 2-layer network architecture, establishing linkages between all access switches (Leaf switches) and aggregate switches (Spine switches), as shown in figure 1. With the above architecture, any two access switches within the data center enable direct communication without any intermediate switches. Also, there is enough bandwidth to ensure effective communication between each access switch and aggregate switch. Further, Spine-Leaf architecture is more friendly for data center expansion by interconnecting different Spine-Leaf networks to realize dynamically phases to construct Internet Data Center according to the demand.

Figure 1 - Traditional 3-layer network architecture vs 2-layer Spine-Leaf architecture

Spine-Leaf Architecture Cabling Solution: Transceiver vs DAC Cable vs AOC Cable

Supported Distance Comparison: Transceiver vs DAC Cable vs AOC Cable

The current network rate has reached 400Gb/s, it can be predicted that Ethernet data will reach 800Gb/s or even 1.6Tb/s in future decades. In the long-distance links of Spine-Leaf and Spine-Core Spine network, transceivers matched with fiber cable solution is still the first choice, which solution has a distinct advantage in transmission distance. According to standard ISO 11801,   the supported distance is up to 2km over single-mode fiber (SMF), up to 300m to 400m in 10G Ethernet, and up to 100m to 150m in 40G/100G Ethernet over multimedia fiber (MMF).

As for the Direct Attach Cables (DAC Cables) and Optical Active Cables (AOC Cables) cabling solution, IEEE specifies DAC cables supported distance up to 7m at 400Gb/s data rate while the AOC cabling solution supports up to 30m. So either DAC or AOC cabling solution is suitable when the link length is within 5m, whereas AOC cabling solution is more applicable in link length of 5m to 30m.

Costs Comparison: Transceiver vs DAC Cable vs AOC Cable

Table 1 shows the price comparison with DAC vs AOC vs transceiver cabling solution of QSFPTEK company. It is obviously found that DAC and AOC cabling systems get a distinct advantage compared with transceiver and fiber cabling systems in diverse data rates. Among the three cabling solutions, the DAC cabling solution gets the lowest cost, which is only about 20 to 40 percent of transceiver cabling systems in diverse data rates transmission. Consequently, in a short-distance link within Top-of-Rack (ToR) switches and server of Spine-Leaf network architecture, DAC and AOC cabling solutions are more cost-saving.

Table 1 - QSFPTEK Cabling Solution Costs: Transceiver vs DAC vs AOC

* Transceiver cabling solution includes two transceivers and one fiber cable.

* The three solutions price in the above table based on a link length of 3m.

Power Consumption Comparison: Transceiver vs DAC Cable vs AOC Cable

Power consumption is always one of the most concerning issues in the industry. The largest expenditure of the Internet Data Center operation and maintenance is electricity expenditure. Table 2 shows the power consumption of DAC, AOC, and transceiver cabling solution. As current Spine-Leaf network architectures are mainly in 10Gb/s and 25Gb/s, it can be found according to the below table that DAC and AOC cabling solution is the better choice than transceiver solution.

Table 2 - QSFPTEK Cabling Solution Power Consumption: Transceiver vs DAC vs AOC

Reliability and Compatibility Comparison: Transceiver vs DAC vs AOC

When it comes to reliability, as the transceiver cabling solution needs to connect the fiber connector to the device interface and keep the optical fiber end face clean, DAC and AOC cabling solutions existing with groupware patterns are more reliable than transceiver cabling solutions.

As for compatibility, transceivers enjoy better compatibility than DAC and AOC cables as the latter adopts the 3rd-party pre-assembled transceiver modules and needs to perform compatibility testing according to the specific brand devices.

Conclusion

From mentioned differences between transceiver fiber cabling solution and DAC and AOC solution, combining the features and requirements of different parts of Spine-Leaf network links, how to choose a suitable cabling solution can be summarized as follow:

a. In the backbone of Spine-Leaf network architecture, as its long-distance transmission and high demand on compatibility, transceivers matched with fiber cabling solution is suggested.

b. In the short-distance links within 7 meters between Leaf switches/ToR switches to servers, DAC cable is suggested with the advantages of cost and power consumption. Significantly, DAC cable structures with coaxial shielded Twinax copper cable, which result in a thick wire and bulky, so not suitable for high-density server deployment.

c. In short-distance Spine-Leaf branch links within 30 meters and links between Leaf switches/ToR to servers beyond 7 meters, AOC cables are suggested. Compared to DAC cables, AOC cables structured with fiber cable are thinner and lighter, which is more suitable for high-density server deployment.

If you have any confusion about the data center cabling solution,  welcome to visit QSFPTEK.COM and consult via sales@qsfptek.com.