MTP 2 interface

The MTP 2 interface consists of messages that govern communications between an application on the host and the MTP 2 task on the TX board.

MTP 2 messages perform the following tasks:

Binding

The binding phase establishes the host application (MTP 3) as the user of the MTP 2 interface. The application sends a single bind request message to MTP 2, for which there is a bind confirmation response. The application must send separate bind request messages to MTP 2 for each link on each TX board that it wants to use.

Establishing a connection

The application establishes a connection by sending a connect request message and attempting to bring up the link and initiate link alignment procedures with the far exchange. MTP 2 sends a connect confirmation message back to the application when link alignment is successfully established. The application requests connections separately for each SS7 link.

No data packets are transferred until the application receives the connect confirmation message. The following illustration shows the message flow for establishing a connection:

Transferring data

After the MTP 2 task returns a connect confirmation message to the application, the application can begin transferring data.

The application sends a data request message to MTP 2 to request transmission of an SS7 packet on a particular link. When a message or messages are acknowledged by the far exchange there is no corresponding notification sent to the application. The following illustration shows the message flow for an outgoing data transfer:

MTP 2 sends a data indication message to notify the application of an incoming data packet. The application does not respond to MTP 2. The following illustrates an incoming data packet notification:

During data transfer, the application can send a flow control request to apply flow control to a link (or to stop flow control). MTP 2 does not respond to the application. MTP 2 can also send an unsolicited flow control indication message to the application to indicate that congestion started or ended on a link.

Status and control

The MTP 2 status request provides the following functions that help MTP 3 implement link and traffic management procedures:

MTP 2 returns a status confirmation message containing the current BSN for a link to the application in response to a retrieve BSN status request. MTP 2 can also return 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. In this case, no status confirmation message is returned to the application. The following illustration shows how to use retrieve status requests to implement link changeover:

Clearing a connection

The application can send a disconnect request message to MTP 2 to disable the link. MTP 2 does not respond to a disconnect request message. MTP 2 can send an unsolicited disconnect indication message to the application to notify it that a link disconnected and the reason for the disconnect.

MTP 2 sends unsolicited status indication messages to the application to notify it of changes in the link status (up or down).

Refer to the MTP 2 message summary for additional information