LU 6.2 API Application Programmer's Reference Guide (30294-90008)

130 Chapter6
Buffer Management
Send Buffer
Send Buffer
For each conversation allocated, LU 6.2 API establishes a send buffer.
On MPE V, the send buffer is always 2044 bytes. On MPE XL, the send
buffer is the same size as the maximum RU size for the session. The
maximum RU size is a configured value from 256 through 2048
associated with the session type. For more information on configuring
RU sizes, see the APPC Subsystem on MPE XL Node Manager’s Guide.
Whenever the MCSendData intrinsic is called, data is transferred to the
send buffer from the
Data parameter specified in the intrinsic call.
When the send buffer is full, LU 6.2 API flushes the buffer and
transmits the data to the remote TP. No data is transmitted until the
send buffer is full or until an intrinsic is called that flushes the buffer.
Example 1: Sending Small Data Records
Figure 6-1 shows how data flows from the send buffer of the local TP to
the receive buffer of the remote TP in a one-way file transfer
application. This example application sends 16-byte data records. The
send buffer in this example holds 2044 bytes.
Figure 6-1 Send and Receive Buffers
Because each data record in figure 6-1 is only 16 bytes long, LU 6.2 API
can store 127 data records in the 2044-byte send buffer (127 records of
16 bytes = 2032 bytes). When MCSendData is called for the 128th time,