How SM Issues Requests

As described in “The SMI” on page 761, each port on a CA or router, as well as the switch management port has an SMI tasked with sending and receiving SMPs. The SMI is always implemented as QP0. As described earlier (see “Managers Use Special Packets Called MADs” on page 27, “Detailed Description of MADs” on page 779, and “SM Methods and Attributes” on page 809), an SMP is a form of MAD and always has a data payload field exactly 256 bytes in length (see Figure 28-1 on page 781). “How the SM Sends a Message and Handles a Response” on page 772 described the basic process the SM uses to construct and send an SMP.