X25AM Programming Manual

PTP Applications
X25AM Programming Manual—527201-001
3-3
Waiting for a Call
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CONTROL 17. A Call Request is sent, and a network response is received. If the
CONTROL 17 completes normally, then the call has been accepted. If it does not
complete normally, the error returned indicates the cause of the failure. Your
application is responsible for determining how the outcome of the procedure call
should be processed.
•
WRITEREAD. The WRITE writes a Call Request (see PTP mode 2 subsection for
detail), and the READ reads the network response. A WRITEREAD can complete
normally yet contain a network response that indicates an error—for example, a
clear indication. Your application is responsible for determining how the outcome of
the procedure call should be processed.
The network response to a Call Request can be one of the following:
•
Call Connected The call was connected.
•
Clear The call was disconnected.
•
Restart The call was cleared by a packet-layer restart.
Waiting for a Call
Your application waits for a call when it has been agreed that the remote device will
start the data exchange. Your application waits for a virtual call with one of the
following file-system procedures:
•
CONTROL 11. An Incoming Call is received, and a Call Accepted is sent. If the
CONTROL 11 completes normally, then the call has been connected.
•
READ followed by WRITE (see PTP mode 2 subsection for detail). The READ
reads the Incoming Call, and the WRITE writes the Call Accepted. If the READ and
WRITE do not complete normally, then the call has not been established. The
application is responsible for determining how the outcome of procedure calls
should be processed.
Exchanging Data
Once the call is connected, your application can exchange data with the remote
device. (An application can communicate any time with a device on a PVC because it
is always connected.) Data exchange is performed with the READ, WRITE, and
WRITEREAD file-system procedures. Data exchange can occur in both directions
simultaneously. Therefore, your application can issue concurrent READs, WRITEs,
and WRITEREADs.
PTP has separate queues for incoming (READ) and outgoing (WRITE) packet
contents. A WRITEREAD starts in the WRITE queue and moves to the READ queue
when the WRITE completes. Queued requests are processed in first-in, first-out order.
Data is exchanged in the form of logical records. Later in this section you will find that
the exchange of data depends on how these records are subdivided. Thus, there are
different modes for the exchange of data.