IPC Flow Control

Using back-pressure, HP OpenCall SS7 provides both inbound and outbound flow control. Inbound flow control is necessary when the application cannot receive all the pending indications in the inbound queue. Outbound flow control becomes necessary when the requests are blocked at the API.

Figure 3-4 Back-pressure

Inbound Path

The application receives single indications from an HP OpenCall SS7 API, even if multiple indications have been generated after the occurrence of a protocol event. A protocol event is a primitive received from the application or from the stack, or simply a timeout.

Indications waiting to be received by the application are maintained by the HP OpenCall SS7 APIs in an inbound queue.

Waiting Indications

As described in “Receiving Signaling Information”, the number of messages waiting to be received are returned to the application. The application must receive all these waiting indications.

TCP Network Back-pressure

If the application does not receive all the pending indications, HP OpenCall SS7 will force back pressure on the LAN and as a consequence on the stack. When a certain period of time elapses, the SS7 stack will delete all the new messages that were not received by the application.

Outbound Path

When a protocol event occurs, HP OpenCall SS7 may generate one or more SS7 messages destined for the network. These messages are placed in the outbound queue. Once all HP OpenCall SS7 processing is completed, the queued messages are sent to the network.

Remaining Messages

If HP OpenCall SS7 has successfully sent all the queued messages, the outbound queue is empty. Otherwise it contains messages that it could not send.

Application Back-pressure

The number of remaining messages is used by HP OpenCall SS7 to accept or reject the service primitives issued by the application. The application is notified by the API of this situation.