When a port's Link Layer receives an inbound request SMP from the SM, it is processed as follows:
1. | The SMP packet is received into the port's VL15 receive buffer. It should be noted that if the buffer is currently full—the minimum required buffer depth is one SMP packet—then the inbound SMP is discarded. |
2. | The SMP's DLID address is used to route the packet. Based on the address in the DLID field, there are three possible cases:
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3. | Upon the SMP's arrival at switch port 0's SMI
RQ Logic, there are two possibilities:
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4. | The packet's 256-byte data payload (the SM
MAD) is passed to the SMA within the switch for processing. |
5. | Refer to Table 28-5 on page 788 and Table 28-6 on page 789. The SMA performs the method specified in the MAD on the specified attribute. The method in an inbound request SMP can be one of the following:
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6. | The SMA swaps the LID addresses (SLID and DLID) that were in the request SMP, sets the BTH:DestQP field to QP0 (the SMI), and passes the packet back to the SMI, which, in turn, passes it to the switch port that received the packet (automatically captured in the PortInfo.LocalPortNum attribute element). That port accepts the packet into its VL15 transmit buffer and transmits the packet. The receiving port's Link Layer accepts the response SMP into its VL15 transmit buffer and forwards the response packet back to the SM. |
A detailed description of Traps can be found in “Traps” on page 790. When a switch experiences an internal event that the SM must be informed of (e.g., a switch port's Link Layer detects that its physical link transitions from the Down to the Up state), the following steps are taken:
1. | The switch's SMA formulates a 256-byte MAD with the following characteristics:
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2. | The SMA passes the 256-byte MAD to port 0's SMI
SQ Logic for transmission. |
3. | |
4. | The SMI's SQ Logic passes the response SMP to the port 0 Link Layer where the packet's DLID is used to perform a lookup in the switch's Forwarding Table. |
5. | The packet is internally forwarded to the switch exit port resulting from the table lookup and is placed in the VL15 transmit buffer of that port's Link Layer. |
6. | The packet is then transmitted to the SM. |