Expand Configuration and Management Manual (G06.24+)

Tuning
Expand Configuration and Management Manual—523347-008
20-8
Application Message Size
As shown in Figure 20-2, the message system recognizes that the data is to be sent to
an application that is not on the local node, and it routes the request to the appropriate
Expand line-handler process.
If the Expand packet size is large enough to hold all of the message from the
application, the Expand line-handler process puts the message into a single packet. If
the Expand packet size is smaller than the message that the application wants to send,
the Expand line-handler process must send more packets across the message system
to the NonStop TCP/IP process.
Expand Subsystem Overhead
It is important to consider Expand subsystem overhead when using facilities with
limited bandwidth. Application message size and Expand packet size have significant
effects on subsystem overhead. The number of Expand packets required for an
application message is calculated using the following formula:
app_msg
is the user message size in bytes.
fsm
represents the file system and Expand message header information (in bytes) sent
at the start of each message.
packet_size
is the maximum number of bytes per packet. If the variable packet size feature is
used, packet_size is the PATHPACKETBYTES modifier value; otherwise,
packet_size is equal to (frame_size - 4 )* 2 where frame_size is the
FRAMESIZE modifier value. The default is 256.
pkt
represents the Expand Layer 2 and packet header information (in words) sent at
the start of every Expand frame.
1 + $INT((app_msg + fsm) / (packet_size - pkt))