MTP 3 -> MTP 2
Requests a special function supported by the MTP 2 layer.
The following table lists the message parameters:
Type |
Field |
Description |
U8 |
Message Type |
0x78 |
S16 |
Service Provider ID |
MTP 2 reference number for the link on the TX board. Valid values are 0 through 15. |
S16 |
Action |
Action to take. Possible values are: 0 = No action; indicate change in status to MTP 2 as specified in Status field 1 = Retrieve backward sequence number 2 = Retrieve unacknowledged messages 3 = Drop all queued transmit messages |
U32 |
Status |
Status change being indicated to MTP 2; relevant if action is 0 or 2. When action = 0, possible values are: 0 = Local processor is down 1 = Local processor is up 2 = Emergency condition 3 = Emergency ceases
When action = 2, the only possible value is the starting sequence number, usually retrieved from an MTP3 COO or COA, which retrieves unacknowledged messages from the board. |
The MTP 2 layer supports the following special functions:
Retrieves the current BSN (last acknowledged sequence number) for a link. This information is used for implementing changeover procedures.
Retrieves all MSUs transmitted on a link but not yet acknowledged, starting from a particular sequence number. This information is used for implementing changeover procedures.
Requests MTP 2 to drop all queued messages.
Notifies MTP 2 of an emergency on or off condition on a link.
Notifies MTP 2 of a local processor up or down condition. This information is passed on to the far exchange.
MTP 2 returns a status confirmation message containing the current BSN (last acknowledged sequence number) for a link to the application in response to a retrieve BSN status request. MTP 2 also returns a status confirmation message in response to a retrieve messages status request, but only if there are no unacknowledged messages to be retrieved. If there are unacknowledged messages to be retrieved, a data confirmation message indicating a status of unacknowledged [more | last] is sent to the application for each message. The last message indicates that it is the last. No status confirmation message is returned to the application.