Cable Connection Solutions in Data center

Currently, in scenarios such as data centers, intelligent computing centers, and HPC, the mainstream network cable connection solutions mainly include:

Optical transceivers + Optical Fiber (Primarily Multimode MMF): This mode is the most widely applied. Due to the separation of optical modules and optical fibers, it offers more flexibility in selection and controllable transmission distance. Disadvantages include high cost, high power consumption, higher insertion loss, and reduced reliability due to potential contamination of optical ports.

AOC (Active Optical Cables): AOCs integrate optical modules and optical cables, avoiding the possibility of optical port contamination to improve reliability. AOC is a cost-performance balanced optimized design solution. It is used for medium to short-distance interconnection scenarios, typically within 100 meters. Features include light weight, long transmission distance, convenient wiring, and insensitivity to electromagnetic radiation. The drawbacks are still relatively high cost and power consumption.

DAC (Direct Attach Cables):

DACs are further divided into passive DACs, active ACCs (Active Copper Cables), and AECs (Active Electrical Cables).

Passive DACs require no optical-electrical conversion, making them the lowest cost option. ACCs use Redrivers to increase transmission distance, while AECs use Retimers for signal reshaping at the receiving end, restoring signals and achieving even longer transmission distances.

Because no optical-electrical conversion is needed, both passive DACs and active ACCs/AECs consume less power compared to optical modules and AOCs. Due to the physical limitations of copper, passive DACs have extremely short transmission distances, and the effective transmission distance decreases as bandwidth increases. In the upgrade from 400G to 800G, the transmission distance will be up to 3m.

Note: Explanation of Redriver and Retimer roles in ACC/AEC A Redriver can be simply understood as a relatively simple signal amplifier. It is an analog signal device that only amplifies signals at the physical layer to compensate for losses caused by cables and connectors. Its advantages are relatively low latency and power consumption, but it amplifies noise and jitter. A Redriver typically includes components such as CTLE (Continuous Time Linear Equalizer, which can be understood as a high-pass filter), broadband gain node (Gain), and linear driver (Driver).

A Retimer is a hybrid digital and analog signal device that extracts the embedded clock from the input signal through its embedded Clock Data Recovery (CDR) circuit and retransmits data using an undistorted clock signal. By restoring data and retransmitting signals through a serial channel, Retimers effectively solve signal attenuation problems. The main difference between Retimers and Redrivers is the inclusion of CDR. The Rx signal in a Retimer is converted to a digital signal before being converted back to an analog signal for transmission, effectively splitting the signal into two segments, theoretically allowing double the cable length, but with higher latency.

The diagram below shows: Redrivers can enlarge and open the eye of the eye diagram, while Retimers can regenerate the signal, resulting in better signal quality.

The following diagram illustrates the implementation of various cable connections:

Customers can choose the most suitable connection solution based on their specific needs, weighing factors such as transmission distance, power consumption, cost, and application scenarios.

The main advantages of copper cable connections are low cost and low energy consumption. However, we also need to recognize that in 800G and future 1.6T scenarios, due to transmission distance limitations, copper cable connections may not even meet the interconnection needs within a single chassis. Therefore, future high-speed connections are more likely to rely on optical fiber connections.

In conclusion, a small advertisement: if you have wiring needs for 100G/200G/400G/800G AOC/DAC/TRANSCEIVERS, feel free to drop me a message or email zoe.zhong@tanlinkoptics.com. Thank you!