Definition of a MAD
Refer to Figure 28-1 on page 781. A Management Datagram (MAD) is always 256 bytes in length and is carried in the data payload field of either an SMP or a GMP. While an SMP MAD only contains an LRH (it never contains a GRH) and cannot be used to address a port outside of the SM's subnet, a GMP can contain a GRH and can be used to address a port outside of the subnet. This means that a GSM can be used to manage devices in multiple subnets.
Figure 28-1. A MAD Is Exactly 256 Bytes in Length
A MAD is generated under the following circumstances:
- The Master SM issues a SM MAD to a device's SMA requesting that a SubnGet() or SubnSet() be performed on the specified device attribute.
- A device's SMA issues a SubnGetResp() SM MAD to the Master SM as a response to a previously received SubnGet() or SubnSet() request MAD.
- A SM issues a SM MAD to another SM requesting that a SubnGet(SMInfo) or a SubnSet(SMInfo) be executed.
- A SM issues a SubnGetResp(SMInfo) SM MAD to another SM as a response to a previously received SubnGet(SMInfo) or SubnSet(SMInfo) request MAD.
- A device's SMA issues a SM SubnTrap(Notice) MAD to inform the SM of an event that has occurred within the device.
- In response to a series of identical SubnTrap(Notice) SM MADs from a specific device, the Master SM issues a SubnTrapRepress(Notice) SM MAD to the device's SMA as a cease-and-desist order.
- A GSM issues a request GMP to the respective GSA within a device requesting that a Get() or Set() be performed on the specified device attribute.
- A device's GSA issues a GetResp() GMP to its respective GSM as a response to a previously received Get() or Set() request GMP.
- A device's GSA issues a Trap(Notice) GMP to inform its respective GSM of an event that has occurred within the device.
- In response to a series of identical Trap(Notice) GMPs from a specific device, the respective GSM issues a TrapRepress(Notice) GMP to the device's GSA as a cease-and-desist order.
- A GSA within a device issues a Send() GMP to transmit an attribute to either a GSA of the same type within another device or to the respective GSM.