NetIPC 3000/XL Programmer's Reference Manual (5958-8600)

Chapter 3 71
NetIPC Intrinsics
IPCCONNECT
handled at the link level and is not normally
required at the user level.
Checksumming is only used for connections between
nodes and is not used for connections within the
same node. Enabling checksumming may reduce
network performance. Recommended value: 0.
opt (input)
Record or byte array, by reference. A list of options,
with associated information. Possible options are:
• call user data (code=2, length=n, n bytes) (input).
For access to the X.25 protocol only. This option
contains data to be inserted as the call user data
(CUD) field in an X.25 packet. The maximum length
for the CUD is 16 bytes. With the fast select facility,
the maximum length for the CUD is 128 bytes. HP
has reserved the first four bytes of the CUD for
protocol addressing. The user can supply data up to
12 bytes (or 124 bytes with fast select). By setting
the no address flag (protocol flags option), the user
can access all 16 bytes (or 128 bytes with fast select)
of the CUD. See Chapter 1 , “NetIPC
Fundamentals.” Access to the Call User Data (CUD)
Field for more information.
• maximum send size (code=3, length=2; 2-byte
integer). (TCP only.) This option, which must be in
the range from 1 to 30,000, specifies the length of the
longest message the user expects to send on this
connection. The information is passed to the protocol
module for internal use only. This does not mean
that the user cannot send a message larger than the
value that is specified in this option code. If this
option is not used, the protocol module will be able to
send messages at least 1024 bytes long. If the value
specified is smaller than a previously specified
maximum send size, then the new value is ignored.
• maximum receive size (code=4, length=2; 2-byte
integer). (TCP only.) This option, which must be in
the range from 1 to 30,000, specifies the length of the
longest message the user expects to receive on this
connection. The information is passed to the protocol
module for calculating its transmission-window size.
This does not mean that the user cannot receive
messages larger than the length specified with this
option code. If this option is not used, the protocol
module can handle messages of at least 1024 bytes
long. If the value specified is smaller than a