SM Control Packets
Definition
An SM uses Control Packets to command another SM to change state (or to acknowledge receipt of a state change command).
How SM Sends a Control Packet
A Control Packet consists of an SMP specifying the following:
SubnSet(SMInfo) operation.
The attribute modifier (in the base MAD header—see Table 28-1 on page 783) is set to one of the values indicated in Table 30-1 on this page.
| Modifier Value | Description |
|---|---|
| 1 | Identifies this as a Handover Control Packet. It is issued by the current Master SM to initiate the process of handing over mastership to a higher-priority Standby or Master SM that was discovered during its periodic sweep or because a trap was received informing the Master of a topology change. |
| 2 | Identifies this as an Acknowledge Control Packet. It is issued by the new Master SM to acknowledge the handover from the old Master SM. |
| 3 | Identifies this as a Disable Control Packet. It is issued by the Master SM to transition an SM currently in the Standby state to the Not-Active state. As an example, there may be multiple Standby SMs generating periodic SubnGet(SMInfo) SMPs to check the Master's ActCount. The Master might determine that they are collectively generating too much unnecessary traffic and, as a result, would issue a Disable Control Packet to one or more of the Standby SMs telling them to cease and desist polling. |
| 4 | Identifies this as a Standby Control Packet. It is issued by the Master SM to transition an SM currently in the Not-Active state to the Standby state. As a result, the Not-Active SM transitions to the Standby state and resumes its periodic polling of the Master's ActCount. |
| 5 | Identifies this as a Discover Control Packet. Upon receipt, an SM currently in the Standby state will transition to the Discovering state. The specification doesn't clarify who might send this packet or why. |
Must an SM Support Control Packets?
The following rules define the SM support requirements:
The ability of a SM to generate SM Control Packets is optional.
The ability to handle receipt of a Control Packet and responding to it is mandatory.
If an SM cannot generate SM Control Packets, it must implement an equivalent mechanism to accomplish the same objectives.
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