Chapter 7 - 4. Congestion Management in Ethernet Storage Networks以太网存储网络的拥塞管理

Ethernet Pause Compared with Fibre Channel B2B Credits 以太网暂停与光纤通道 B2B 信元的比较

Although Ethernet Pause frames and Fibre Channel B2B credits operate differently, they achieve hop-by-hop flow control by notifying the directly connected sender to slow down so that the receiver does not run out of its buffers. 虽然以太网暂停帧和光纤通道 B2B 信元的操作方式不同，但它们都是通过通知直接连接的发送方放慢速度，以避免接收方的缓冲区耗尽，从而实现逐跳流量控制。

The following points compare Ethernet Pause to Fibre Channel B2B credits: 以下几点对以太网暂停和光纤通道 B2B 信元进行了比较：

1. Initial exchange: Fibre Channel B2B credit number is communicated to the directly connected neighbor during link initialization. In contrast, the Ethernet flow control doesn’t exchange the number of buffers with the directly connected neighbor, although DCBX may exchange other information such as the type of traffic that needs lossless behavior. 光纤通道 B2B 信元号在链路初始化期间与直接连接的邻居进行通信。相比之下，以太网流量控制不会与直接连接的邻居交换缓冲区数量，尽管 DCBX 可能会交换其他信息，如需要无损行为的流量类型。

2. Link utilization: Fibre Channel R_RDYs do not contribute to the link utilization because they are primitives and use the place of a fill word between two frames. On the contrary, Pause is a proper Ethernet frame with a header, padding, and CRC. The size of a Pause frame is 64 bytes. Hence, when Pause frames are sent in large number, they contribute to the link utilization. The later section on PFC storm explains a scenario when one million Pause frames may be sent on a link every second. This would lead to a throughput of 512 Mbps (64 bytes x 8 x 1000,000). Although less common, be aware of this aspect when many Pause frames flow on a link. 光纤通道 R_RDY 不影响链路利用率，因为它们是基元，在两个帧之间使用填充字。相反，暂停是一个正式的以太网帧，带有报头、填充和 CRC。暂停帧的大小为 64 字节。因此，当大量发送暂停帧时，会增加链路利用率。在后面有关 PFC 风暴的章节中，将解释每秒在链路上发送一百万个暂停帧的情况。这将导致 512 Mbps 的吞吐量（64 字节 x 8 x 1000,000）。虽然这种情况并不常见，但当许多暂停帧在链路上流动时，还是要注意这方面的问题。

3. Duration exchange: Ethernet Pause frame conveys the duration for which the transmitter must stop transmission, although this duration rarely conveys the actual time the traffic was paused. Fibre Channel R_RDYs do not convey a duration. 以太网暂停帧传达发送器必须停止传输的持续时间，尽管该持续时间很少传达流量暂停的实际时间。光纤通道 R_RDY 不传递持续时间。

4. When they are sent: Fibre Channel R_RD