Expand Configuration and Management Manual (G06.24+)

Subsystem Description
Expand Configuration and Management Manual—523347-008
18-40
Outgoing Traffic Flow
password exists for the destination node, the request is completed with an error (file-
system error 48, security violation) and is not sent.
If the COMPRESS_ON modifier is set, the Expand line-handler process attempts to
compress the data in the message. When compression is configured, groups of
consecutive zeros (0), spaces, and NULLs are replaced with indicator and count
values. These values are removed and replaced with the original characters when the
message is received and decompressed by the destination Expand line-handler
process.
The Expand line-handler process prioritizes each outgoing message according to the
message’s Expand priority, which is based on the priority level of the application
process that created the message, unless the SETMODE 71 procedure is used.
SETMODE 71 can be used to assign to a message a priority level that is higher or
lower than the application process priority.
Once the security check, data compression, and message prioritization have been
performed, the Expand line-handler process queues the message to its list of outgoing
messages for the destination node. When a message is queued to the outgoing
messages list, it occupies buffer space in the Expand line-handler process buffer pool.
The Expand line-handler process formats the highest-priority message into standard
size-and-format transmission units, called packets. Messages that are too large to fit
into one packet are fragmented into as many packets as are required to contain the
entire message.
Packets are sent sequentially until the total message is sent. The Expand line-handler
process does not mix packets from different locally originated messages, but it may
interleave packets from locally originated messages with passthrough and $NCP
packets. ($NCP and passthrough traffic flow is discussed in $NCP and Passthrough
Traffic Flow on page 18-41.)
When all the packets that make up the total message have been sent, the Expand line-
handler process queues the message to its list of unacknowledged messages. When
the Expand line-handler process receives an acknowledgment from the destination
node for the message, it processes the message differently depending on whether the
message is a request or a reply to a previous request.
If the message is a request, the Expand line-handler process queues the message to
its list of messages waiting for replies and does not release the buffer pool used by the
message. If the message is a reply, the Expand line-handler process releases the
buffer pool used by the message.
Note. The Expand line-handler process buffer pool is explained in Message Buffering on
page 18-46.
Note. The Expand line-handler process obtains packet-size information from the value
assigned to the FRAMESIZE or PATHPACKETBYTES modifier.