Chapter 2 - 2. Understanding Congestion in Fibre Channel Fabrics

 B2B credits are not negotiated, just communicated: Contrary to common belief, directly connected neighboring FC ports don’t negotiate B2B credits. Rather, the number of Rx B2B credits is communicated or informed to the neighbor, which the neighbor uses as the Tx B2B credits. An FC port simply accepts whatever number is conveyed to it by its neighbor. It can’t request to change this number, and thus, this process can’t be called a negotiation. For example, an HBA port (N_Port) may communicate or inform to the switchport (F_Port) that it has 8 Rx B2B credits. The switchport uses this information to set its Tx B2B credits to 8. The switchport can’t change its Tx B2B credits by itself. The only way to change the Tx B2B credits on this switchport is to change the number of Rx B2B credits on the HBA port and re-initialize the link for this change to take effect. 与通常的看法相反，直接连接的相邻 FC 端口不会协商 B2B 信元点数。相反，Rx B2B 信元点的数量会传达或通知给邻居，邻居将其用作 Tx B2B 信元点。FC 端口只需接受邻居传达给它的数字。它不能要求更改这个数字，因此这个过程不能称为协商。例如，HBA 端口 (N_Port) 可以向交换端口 (F_Port) 传达或告知它有 8 个 Rx B2B 信元点数。交换端口使用此信息将其 Tx B2B 点数设置为 8。交换端口无法自行更改其 Tx B2B 信元点数。更改该交换端口上 Tx B2B 点数的唯一方法是更改 HBA 端口上的 Rx B2B 信元点数，并重新初始化链路以使更改生效。

 B2B credits are defined by the manufacturer: The default number of Rx B2B credits on a port is defined by the manufacturer. Some products allow changing the number of Rx B2B credits, but the extent of this change is defined by the capability of the pro

原文地址：https://blog.csdn.net/mounter625/article/details/142716034

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