Modified TCP Implementations
Standard TCP with ECN detects the presence of congestion and reacts to it by reducing the congestion window as if packets had been dropped. In data center environments, where the links are of high capacity and end-to-end delay is low, the standard TCP congestion control mechanisms, such as reducing the congestion window by half, maybe an overreaction leading to underutilization of the links. Also, ECN conveys only the presence of congestion. It does not convey the extent or severity of congestion. 带有 ECN 的标准 TCP 可检测到拥塞的存在，并通过减少拥塞窗口（就像丢弃数据包一样）对其做出反应。在数据中心环境中，链路容量大，端到端延迟低，标准 TCP 拥塞控制机制（如将拥塞窗口减半）可能会反应过度，导致链路利用率不足。此外，ECN 只表示存在拥塞。它并不表示拥塞的范围或严重程度。
Hence, like TCP implementation on Cisco FCIP switches, modified TCP implementations may be available on the end devices for intra-data center communication. Data Center TCP (DCTCP) is one such example. It is described in an information RFC 8257, but it is not standardized. 因此，与思科 FCIP 交换机上的 TCP 实现一样，终端设备上也可以使用修改过的 TCP 实现，以实现数据中心内部的通信。数据中心 TCP (DCTCP) 就是这样一个例子。信息 RFC 8257 对其进行了描述，但并未标准化。
DCTCP changes traditional ECN processing by estimating the fraction of bytes that encounter congestion rather than simply detecting that some congestion has occurred. DCTCP then scales the TCP congestion window based on this estimate. This method achieves high-burst tolerance, low latency, and high throughput within a data center network. DCTCP 改变了传统的 ECN 处理方式，它估算遇到拥塞的字节数，而不是简单地检测是否发生了拥塞。然后，DCTCP 根据这一估计值调整 TCP 拥塞窗口。这种方法可在数据中心网络内实现高突发容错、低延迟和高吞吐量。
The only difference between a DCTCP sender and a standard TCP sender is in how each reacts to receiving an ACK with the ECN-Echo flag set. This is explained earlier in the section on Explicit Congestion Notification in TCP/IP Networks. Other features of TCP such as slow start, additive increase in congestion avoidance, or recovery from packet loss are left unchanged. While standard TCP reduces its window size by half, DCTCP reduces the window only slightly during low severity of congestion. When congestion is severe, DCTCP reduces the window to half, just like standard TCP. DCTCP 发送方与标准 TCP 发送方的唯一区别在于，各自如何对收到设置了 ECN-Echo 标记的 ACK 作出反应。这一点在前面 "TCP/IP 网络中的显式拥塞通知 "一节中已有解释。TCP 的其他功能，如慢速启动、拥塞避免的累加增加或数据包丢失后的恢复，则保持不变。标准 TCP 会将窗口大小减半，而 DCTCP 只在拥塞严重程度较低时稍微减小窗口。当拥塞严重时，DCTCP 会像标准 TCP 一样将窗口减半。
Although modified TCP implementations, such as DCTCP, may deliver better performance, their use must be carefully analyzed because of the following reasons: 虽然修改后的 TCP 实现（如 DCTCP）可以提供更好的性能，但由于以下原因，必须对其使用进行仔细分析：
1. Configuration overhead: DCTCP or similar modified TCP implementations may not be enabled by default. Hence, using them involves a configuration overhead of enabling them on all devices. DCTCP 或类似的修改 TCP 实现可能不会在默认情况下启用。因此，使用它们需要在所有设备上启用这些配置。文章来源：https://www.toymoban.com/news/detail-842782.html
2. Expertise: Deploying DCTCP or similar mo文章来源地址https://www.toymoban.com/news/detail-842782.html
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