As network architectures continue to evolve, 40G Ethernet is an important stage in the transition between 10G and 100G. During this process, multiple 40G interface standards, such as SR4, LR4, ER4, and ZR4, have emerged for different transmission distances, fiber types, and application scenarios, and are designed to meet a variety of needs ranging from short-distance communication in data centers to long-distance transmission in metro WANs. Therefore, when deploying a network, understanding the differences between the standards and making the right choice based on the specific environment are key to ensuring efficient and stable network operation.
Overview of Mainstream 40G Standards
Before we get into ZR4, let’s quickly review the other major 40G Ethernet standards on the market. First up is 40GBASE-SR4 (Short Reach 4), which uses multimode fiber (MMF) for transmission and is typically used for inter-rack connectivity within data centers over distances of around 100 meters. Due to its low cost and low power consumption, SR4 is widely used for short-reach communication between high-speed switches.
Next is 40GBASE-LR4 (Long Reach 4), a standard that uses single-mode fiber (SMF) to support transmission distances of up to 10 kilometers, and is suitable for remote connections between campus networks or data centers. And 40GBASE-ER4 (Extended Reach 4) further extends the transmission range by supporting links up to 40 kilometers, which is suitable for larger urban network deployments.
40GBASE-ZR4, as the “king of long distance” among these standards, increases the transmission distance to 80km on a single fiber, making it ideal for service providers, financial institutions, government agencies and other organizations to build a wide-area backbone network.
Technical differences between ZR4 and other standards
From the perspective of technical implementation, ZR4 and ER4 are very similar in structure, both based on four 10Gbps optical signal channels transmitted over a single fiber via wavelength division multiplexing (WDM). However, the 40G QSFP+ ZR4 employs denser DWDM wavelength planning as well as higher power optical transmitters and more sensitive receivers to cope with the optical attenuation associated with transmission over long distances of up to 80 kilometers. In addition, ZR4 modules tend to have a stronger forward error correction (FEC) mechanism built in, which further improves BER resistance and ensures data integrity.
In contrast, SR4 uses parallel multimode channels and does not use wavelength division multiplexing, resulting in low power consumption and lower cost; however, its distance is limited and it is only suitable for use within data centers. And although LR4 uses single-mode fiber and WDM technology, it is targeted for short- and medium-distance transmission, and its transmission capability is clearly inferior to that of ZR4.
In terms of packaging, SR4 and LR4 are mostly QSFP+ modules, while ZR4 initially appeared in the form of CFP/CFP2 packages, but in recent years it has gradually evolved to QSFP+ to adapt to the increase in equipment density and module standardization trends.
Comparative Analysis of Actual Deployment Scenarios
The selection of different standards is often directly related to the application environment: SR4 is suitable for high-speed short-distance interconnection between servers, switches and other equipment, with flexible installation and low cost; LR4 is suitable for large-scale campus or inter-campus communication between data centers to meet the demand for medium-distance without the need for trunking; and ER4 meets the demand for city-wide distributed networks, and is often used to connect data centers that are located in the same city but geographically dispersed. It is often used to connect geographically dispersed data centers located in the same city.
The ZR4 is the most cost-effective choice when transmission needs extend across a city, even connecting suburban or remote office locations. ZR4 offers a simplified plug-and-play solution that reduces network architecture complexity compared to deploying repeaters or using complex DWDM transport systems.
Status of Standardization and Market Support
It should be noted that unlike SR4, LR4 and other interfaces standardized by IEEE, ZR4 is not an official standard and is mostly defined by optical module vendors. This means that the compatibility between the module and the network equipment needs to be paid attention to when deploying, so as to avoid adaptation problems after procurement.
Although ZR4 is not yet fully popular, it has a stable market in specific industries, especially in the financial industry, government data networks, research institutions and large enterprises with remote data interconnection scenarios. Some vendors have launched stable ZR4 module products and support standard MTP or LC interfaces for easy integration with existing fiber optic systems.
Selection Recommendations and Future Outlook
When evaluating whether to use ZR4, organizations need to weigh a number of factors, including budget, transmission distance, network scalability and future evolution plans. If the current network architecture is still predominantly 40G and there is a need to interconnect data centers over long distances, ZR4 provides a problem-oriented solution that can be solved without a full upgrade to 100G. ZR4 offers long-term operational and fiber utilization advantages over deploying multiple ER4 modules or repeaters.
However, given the gradual price drop of 100G modules, new projects built for the future may prefer to go straight to 100GBASE-LR4 or ZR4, simplifying the future upgrade path.
Summary
As a 40G Ethernet solution designed for long-distance transmission, 40GBASE-ZR4 is a non-standard interface, but it still has irreplaceable value in specific scenarios due to its excellent transmission capability and mature technology foundation. Compared with standards such as SR4, LR4, ER4, etc., it provides the maximum transmission distance and system simplification capability, which makes it suitable for use in specific industries and demanding network environments. In the process of network deployment, it is important to understand the technical differences and application scenarios of each standard in order to make the most reasonable choice and build a modern network architecture that is both stable and scalable.
