The HP OpenCall SS7 ISUP library provides both inbound and outbound flow
control via back-pressure.
Inbound flow control is necessary when the application cannot
read all the pending message indications
found in HP OpenCall SS7 ISUP’s inbound queue. On the outbound path,
flow control becomes necessary when the application requests are
blocked at the MTP3 interface.
Inbound
Path |
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The application receives single primitives from the HP OpenCall SS7 ISUP API,
even if multiple primitives
have been generated after the occurrence of a protocol event.
A protocol event could be a primitive received from either the application
or the network, or simply a timeout.
Primitives waiting to be received by the application are maintained
by HP OpenCall SS7 ISUP in an inbound
queue.
With each IsupSMProbe::receive()and IsupBPProbe::receive(), the number of indications waiting
to be received is also passed, see “Receiving Messages”. It is your responsibility to repeatedly call
receive() until all the waiting indications have been received.
While there are still indications waiting to be received by
the application, MTP3 will not perform a MTPL3recv() on behalf of HP OpenCall SS7 ISUP.
If the application does
not receive all the pending primitives as soon as possible,
the back pressure HP OpenCall SS7 ISUP forces
on the network will cause the SS7 stack to delete
all new messages that it cannot send to HP OpenCall SS7 ISUP within
a certain period
of time.
Outbound Path |
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When a protocol event occurs, HP OpenCall SS7 ISUP state-machines may
generate one or more ISUP messages destined for the network. The generated
messages are placed in an outbound queue
by the processing state-machines.
Once the state-machines have completed their processing, HP OpenCall SS7 ISUP attempts
to send all
the messages in the queue to the network.
If HP OpenCall SS7 ISUP is successful in sending all the messages, the queue
is empty. Otherwise, it contains the messages that it could not send.
Application
Back-pressure
The number of remaining messages in the queue is used by HP OpenCall SS7 ISUP to accept or
reject the service primitives that
the application issues.
When the application issues a send(), HP OpenCall SS7 ISUP determines whether the queue
is empty or not. If it is not empty, then the send() fails with the Return
Status value IPC_SEND_FULL.
However terminating primitives
can be sent from the application to HP OpenCall SS7 ISUP library when this IPC congested
state occurs. These primitives are:
When the congestion disappears, HP OpenCall SS7 ISUP immediately calls s(endPossible), indicating to the application via the activity object
mechanism that it can restart sending messages.
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