In the Japanese VPS server market, common mainstream network providers include SoftBank, IIJ, NTT, and KDDI. Among them, SoftBank and IIJ are considered by many users as preferred options that balance stability and price/performance ratio. What are the differences between SoftBank and IIJ? Which is better in terms of stability, cross-border connection back to China, latency when accessing from mainland China, network jitter and packet loss rate, bandwidth, and outbound quality?

　　First, it's important to clarify that network quality is neither absolute nor fixed. It is affected by multiple variables, including the city where the data center is located, the outbound provider, peering network arrangements, optimization of the backbound connection to China, and the network operator of the target access location. Therefore, even within SoftBank, performance can vary depending on the service provider, time of day, and the domestic network access location. The same applies to IIJ. We are discussing overall trends and common performance of most users/data centers, not guaranteeing perfect performance every time.

　　Comparing SoftBank and IIJ, let's first look at their respective network infrastructure and the features claimed by their official websites/service providers. IIJ is a long-established Japanese ISP/backbone network service provider. Its IP-Transit service offers thousands of routes/prefixes, is peering with multiple mainstream NSPs and CSPs, and boasts redundant links and a high SLA commitment—its official website states that its backbone network is high-quality, low-latency, and low-jitter. In other words, from a backbone perspective, IIJ's network capacity and stability are strongly guaranteed.

　　On the other hand, SoftBank lines (usually known as SoftBank BB / BBTEC / SoftBank JP, etc.) are often branded by Japanese VPS service providers as "premium return routes to China," lines optimized for mainland China users—user tests have shown that SoftBank offers lower latency and less jitter for mainland China Telecom/Unicom users returning to China.

　　From the two key dimensions of latency and stability, we compared several publicly available data sources and user community/testing experiences:

　　According to SoftBank's network assessments and user reports, its average latency for connections to mainland China (especially China Telecom/China Unicom users) is in the range of 50–70ms (China Telecom users) or 60–80ms (China Unicom users), with good stability during off-peak hours.

　　Because SoftBank's lines are "paid premium bandwidth," compared to ordinary international best-effort lines, jitter and packet loss rates are relatively lower during peak hours or periods of intense bandwidth competition. IIJ emphasizes its backbone redundancy, wide peering network, multiple prefixes, and stable outbound connections in its official service, claiming 99.9999% availability and low latency and low jitter.

　　In some user tests, Japanese VPSs using IIJ lines also maintain relatively stable access performance when connecting to China, especially during off-peak hours, with stable network and low packet loss.

　　This shows that both SoftBank and IIJ position themselves as "premium/high-quality/stable/optimized lines," a level above ordinary low-cost international lines. The difference lies in their focus: SoftBank emphasizes optimization for users accessing mainland China—making it more user-friendly for those sensitive to jitter and latency, and those accessing mainland China; IIJ prioritizes backbone quality and wide-area export stability—advantageous for global access, stable export, and enterprise/cross-border access.

　　Next, considering practical application scenarios and potential risks, we'll compare which uses each is more suitable for:

　　When you primarily serve users in mainland China and require fast return speeds, high stability, low latency, and minimal jitter—SoftBank is often the better choice. It's particularly suitable for web services primarily serving mainland China users, e-commerce websites, content distribution, API services, cross-border e-commerce backends, game acceleration nodes, video/streaming synchronization, accelerator services, etc. SoftBank's optimization for users accessing mainland China significantly improves the user experience compared to ordinary international lines.

　　When you require a server with stable international connectivity, access to multiple regions globally/Asia, balanced export quality, and reduced jitter during cross-border access—IIJ's strong backbone, stable export, and good network redundancy make it ideal for these needs. It's particularly suitable for cross-border SaaS, global API services, cross-regional data synchronization, global CDN origin nodes, relay nodes, and services with high stability requirements.

　　However, SoftBank isn't entirely superior to IIJ—its "friendliness" is more evident in its optimization for return routes from mainland China. If your access targets are primarily Europe, America, and Southeast Asia, or if your server is used for international access, SoftBank's optimization for return routes may offer limited help, and its overall international export performance may not be better than regular lines. On the other hand, while IIJ performs stably in terms of backbone network and peering connections, its performance for return routes from mainland China may not be as friendly as SoftBank's, with potentially slightly higher latency/jitter. Additionally, factors such as peak hours, ISP interconnection status, domestic visitor network operators (China Telecom/China Unicom/China Mobile), whether the VPS provider has actually purchased high-quality export bandwidth/whether congestion is occurring, and the stability of the data center and export lines should also be considered. Even a theoretically high-quality network can lead to a poor user experience if the specific service provider uses oversold bandwidth, shares the egress bandwidth, or has poor peering.

　　Therefore, when making a practical choice, I suggest evaluating and deciding based on the following:

　　First, clearly define your primary user group. If they are mainly users in mainland China, SoftBank is preferable; if they are global users or distributed across multiple regions, IIJ is a safer option.

　　Focus on whether the service provider truly provides "optimized/high-quality/dedicated/native egress bandwidth," rather than simply using the "SoftBank" or "IIJ" label—pay particular attention to whether the bandwidth is shared, whether the egress bandwidth is oversold, and whether there are shared nodes.

　　Before making a decision, conduct ping/traceroute/mtr/multi-ISP tests using nodes from different networks in mainland China (China Telecom/China Unicom/China Mobile) to test latency, jitter, and packet loss rate to verify whether the actual performance meets expectations.

　　Considering business type and traffic characteristics—high concurrency, real-time interaction (such as games, live streaming), cross-border connectivity, streaming media, and API services have high stability requirements; static content, low-concurrency sites, and testing environments have higher tolerance and can be compromised appropriately.

　　In summary, both SoftBank and IIJ VPS lines in Japan have their advantages and disadvantages. Both belong to the "premium/high-quality/stable/optimized" tier of Japanese servers, offering significant advantages over ordinary international best-effort lines. If your service primarily targets users in mainland China, SoftBank, with its optimization for returning to China and lower latency and less jitter, is often the optimal solution. If you require stable international access, cross-regional connectivity, and high backbone quality, then IIJ is a more balanced, reliable, and suitable choice for enterprise/multi-region/global user scenarios.