Q: Isn’t increasing network capacity the ultimate solution to network congestion?

Increasing network capacity is the solution when a lack of network capacity is the root cause of congestion. There are many more reasons for network congestion and in those cases, increasing network capacity does not solve this problem. For example, in lossless networks, such as Fibre Channel, congestion due to slow-drain happens even when network capacity is not a limiting factor. 当网络容量不足是造成网络拥塞的根本原因时，增加网络容量就是解决办法。造成网络拥塞的原因还有很多，在这些情况下，增加网络容量并不能解决问题。例如，在无损网络（如光纤通道）中，即使网络容量不是限制因素，也会发生因慢排空而导致的拥塞。

Additionally, consider the following points. 此外，还要考虑以下几点。

1. Applying the solution involves practical challenges of production environments which may seem trivial until you experience them. First, finding the cause and the source of congestion may take a long time. This is important because you need to know where to add the capacity. Congestion detection and troubleshooting methodology explained in this book help with this. Then, upgrading the network links may not be immediately possible because funds to buy new components may not be readily available or the shipment of the components may be delayed. Further, users must find a change window, which typically requires coordination among various teams. Especially, if the upgrade is needed on the hosts that run business-critical applications, approvals may be delayed by weeks or even months. During this long delay, allowing the network congestion to victimize the applications is unacceptable. Hence, the need for congestion prevention mechanisms in addition to an upgrade. This reality is not very different from the congested roads in large cities across the world. Adding more lanes or newer roads seems like a simple solution but this construction is expensive and takes a long time. Hence, many cities us