Request-timeouts
The show logging onboard flow-control request-timeout command indicates that an ingress interface wants to send frames to an egress interface but it is not receiving a grant from the central arbiter to allow it to transmit to the egress interface. Refer to Chapter 2, the section on Frame Switching Within a Cisco MDS switch for more details about the central arbiter and how the grant works. show logging onboard flow-control request-timeout 命令表明，入口接口希望向出口接口发送帧，但它没有收到中央仲裁器允许它向出口接口传输的授权。有关中央仲裁器和授予工作原理的详细信息，请参阅第 2 章 "Cisco MDS 交换机内的帧交换 "一节。
When an ingress interface receives a frame, it determines the egress interface and sends a request to the Central Arbiter. If the egress interface has sufficient buffer space to hold the frame, the Central Arbiter returns a grant to the ingress interface and the ingress interface transmits the frame to the egress interface through the internal switching infrastructure (crossbar). If the egress interface does not have sufficient buffer space to hold the frame, the Central Arbiter does not return a grant. The ingress interface waits a small amount of time and resends the request. Again, if the egress interface still does not have sufficient buffer space to hold the frame, the Central Arbiter continues to not return a grant. This process repeats until the egress interface can accept the frame and the arbiter returns a grant. 当入口接口收到帧时，它会确定出口接口并向中央仲裁器发出请求。如果出口接口有足够的缓冲空间容纳帧，中央仲裁器就会向入口接口返回授予，入口接口就会通过内部交换基础设施（交叉条）将帧传输到出口接口。如果出口接口没有足够的缓冲空间容纳帧，则中央仲裁器不会返回授予。入口接口等待一小段时间后重新发送请求。同样，如果出口接口仍然没有足够的缓冲空间来容纳帧，中央仲裁器将继续不返回授予。这一过程不断重复，直到出口接口可以接受帧，仲裁器才返回授予。
Refer to Example 4-10. The ‘Dest Intf’ fc1/47 is the congested port and fc1/1-fc1/16 are the ports that are attempting to send traffic to fc1/47. It would be expected to find either high Tx-datarate or high TxWait on fc1/47 at the time stamps shown. 请参阅例 4-10。Dest Intf' fc1/47 是拥塞端口，fc1/1-fc1/16 是试图向 fc1/47 发送流量的端口。在所示的时间戳上，预计 fc1/47 上会出现高 Tx-datarate 或高 TxWai