Next-Gen Data Transfer: SFP112/QSFP112/QSFP-DD800/OSFP 800G DAC

With the advent of the big data era and the rapid development of data centers, Direct Attach Cables (DAC), also known as direct attach cables or high-speed cables, have become increasingly popular in large-scale data centers due to their significant price advantage and fast, secure, and reliable transmission characteristics. They have taken a significant share in large-scale data centers. high-definition live streaming, AI, IoT, and other 5G network applications continue to develop rapidly, there is a growing demand for higher transmission speeds in large-scale data centers.

In data centers, routers and switches have interfaces on the I/O panel side, and the connections between network devices (interconnected through IO interfaces) mainly rely on two types of connections: copper cable connections and fiber optic connections. Due to the high cost of fiber optics, an ideal solution for short-distance transmission within or between cabinets is DAC (high-speed cables). Furthermore, as the single-link signal rate evolves from 56Gbps to 112Gbps, and I/O interfaces of network devices upgrade from 400G to 800G, a direct consequence is a sharp increase in link loss, resulting in shorter transmission distances for passive copper cable I/O modules.

The four high-speed copper cable solutions mentioned above have the following characteristics:

• UsingFiberMall’s self-developed High Speed 112 series high-speed bare wire, which has excellent performance.
• The transmission encoding adopts PAM4-112G technology, supporting up to 40GHz pre-resonance (Suck-out), and is backward compatible with QSFP56 and QSFP28.
• The products comply with the IEEE 802.3ck specification, with a maximum transmission rate of 800Gbps and backward compatibility with 400G products.
• The insertion loss is less than 19.75dB@26.56GHz, and under the condition of stacking 8 near-end crosstalk and 7 far-end crosstalk, the Channel Operating Margin (COM) is better than 4dB.

The specific DAC technical specifications include:

• SFP112             30AWG-1.5M / 28AWG-2.0M
• QSFP112           30AWG-1.5M / 28AWG-2.0M
• QSFP-DD800      30AWG-1.5M / 28AWG-1.5M
• OSFP 800          30AWG-1.5M / 28AWG-2.0M

FiberMall QSFP112 26AWG 2M Product Test

112G High-Speed Interconnect Copper Cable Technology

Introduction of High-Speed Copper Cable

High-speed copper cable generally refers to DAC (Direct Attach Cable), which is a direct cable or direct copper cable. It uses silver-plated conduct and foamed insulation cores and adopts wire pair shielding and overall shielding to form a high-speed cable. Compared to optical modules, high-speed copper cables do not have expensive optical lasers and other electronic components, thus significantly saving costs and power consumption in short-distance applications. They serve as low-cost and efficient communication solutions that can replace optical modules.

High-Speed DAC Main Components

QSFP112G DAC

However, with the increase in transmission rates, the overall link imposes stricter requirements on cable loss. Conventional copper cables are no longer able to cover long-distance applications within data center cabinets. This has led to the emergence of active copper cables with linear gain, such as Active Copper Cable (ACC), and even more powerful active copper cables with CDR (Clock Data Recovery) called Active Electric Cable (AEC). The principle of ACC is to add linear compensation (CTLE) to the receiving end of the cable through analog means to compensate for high-loss situations in copper cable applications and meet the link requirements of the system. The principle of AEC is to add CDR or more complex digital signal processing (DSP) algorithms at both ends of the cable. It performs pre-emphasis, de-emphasis, recompilation, and re-driving of the input and output signals, effectively isolating jitter and noise, and achieving higher signal-to-no ratio (SNR) transmission.

ACC Signal Transmission Principle with Linear Gain

AEC (CDR or CDR+DSP Active Copper Cable Signal Transmission Principle)

Application Overview of High-Speed Copper Cable

70% of the internet traffic occurs within data centers, so the interconnection technology within data centers needs to keep up with the increasing data flow. Large-scale internet data centers have been the fastest-growing market in terms of interconnection and the field with the most rapid technological innovation in recent years. In the current popular CLOS data center network architecture, the proportion of links using short-to-long-distance optical modules between the Leaf and Sp layers is approximately one-third of the total number of links between access layer switches and servers. For servers and TOR switches, which account for the majority of interconnection usage, high-speed copper cables (DAC/ACC/AEC) and active optical cables (AOC) can be used for interconnection, covering distances of up to 20 meters. Passive copper cables (DAC) have natural advantages over active optical cables (AOC) in terms of low failure rate, low power consumption, and low cost. With the current requirement for “carbon neutrality,” the Power Usage Effectiveness (PUE) of data centers has become a key metric for measuring data center operational efficiency. In recent years, with the construction and establishment of large-scale/ultra-large-scale data centers, advanced integrated design has significantly increased the power capacity of individual server cabinets, thereby effectively reducing the vertical cabling distance for server access (by adjusting the deployment location of TOR switches). With the deployment of white-box network devices and custom computing nodes, DAC or DAC+ACC solutions have been widely used for server network access links within cabinets, meeting the requirements of high reliability, low cost, and low power consumption for data center construction.

Typical Data Center Network Architecture 1

Typical Data Center Network Architecture 2

The diverse range of high-speed copper cable interface types in the 112G series provides a variety of options for different architectural levels and application scenarios. Based on years of market experience and analysis of the design characteristics of various high-speed copper cable interfaces, the mainstream high-speed copper cable interfaces in the 112G PAM4 generation are based on 400G, QSFP-DD 800G, and OSFP 800G. Additionally, there are parallel iterations of SFP112G/SFP-DD112G/DSFP112G.

Interface industry-standard reference

High-Speed Copper Cable Design

The highly compatible iterative upgrade of the 112G PAM4 high-speed copper cable solution ensures a stable migration of the new generation of external high-speed copper cable technology. The new solution is designed based on the requirements of the existing product family, combined with the existing structural characteristics for upgrading and evolution. While improving the speed, it also ensures the continuity of management interfaces and pin definitions.

Copper Cable Structural Design

Based on different application environments, various forms of OSFP and QSFP-DD products have been derived. The design of multiple forms is based on the consideration of the module’s heat dissipation requirements. Considering that the power consumption of passive copper cables is very low (milliwatts level) and taking into account the normalization of product forms promotes the healthy development of products and the market, QSFP-DD Type1 and OSFP Open Top are generally preferred models for passive copper cables (taking QSFP112G as an example).

QSFP112 Dimension Reference

Copper Circuit Design

QSFP112 Pin definition

Example QSFP112 Host Board Schematic for Passive Copper Cables

Management Interface Standard

EEPROM Map Reference Specifications

For the above, refer to SFF-8636 Management Interface for Cabled Environments Rev 2.9.

CMIS Module Memory Map

For the above, refer to Common Management Interface Specification Rev 4.0.

Testing and Certification of High-speed Copper Cables

In order to ensure the unity and standardization of the certification process of high-speed cables, based on the premise of EIA-364 test standard requirements, combined with the design and application characteristics of external high-speed copper cables, the electrical, mechanical, and environmental reliability requirements.

1. Signal Integrity Test Item Requirements and Methods

The following items are the test data of TP1-TP4, including MCB PCB alignment and connector, as shown in the following figure:

Test specifications:

2. Electrical Reliability Test Requirements

3. Mechanical Reliability Test Requirements

4. Environmental reliability test requirements

5. Liquid-cooled compatibility test requirements