Expand Configuration and Management Manual (G06.24+)

Subsystem Description
Expand Configuration and Management Manual—523347-008
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Global Variables
Global Variables
The global variables space contains the Expand subsystem software global variables.
The Expand subsystem determines how much global variables space to allocate
according to the number of lines in a path controlled by the Expand line-handler
process.
Stack
The Expand subsystem allocates 700 words to the stack.
Control Blocks
The Expand subsystem preallocates space for many data structures that are likely to
be used during normal operation.
Line Buffer
The line buffer is used to buffer incoming and outgoing messages after they have been
formatted into packets by the Expand line-handler process. The line buffer for Expand-
over-NAM, Expand-over-ServerNet, and Expand-over-FOX line-handler processes is
located in the Expand line-handler process data space.
Read frame buffers are used to buffer incoming messages; write frame buffers are
used to buffer outgoing messages. In most cases, the Expand subsystem allocates
enough buffer space for the maximum number of read and write frame buffers. You can
adjust this with the TXWINDOW modifier. If you are using a satellite connection (which
uses the maximum window size of 61 frames) with a FRAMESIZE modifier value of
over 512 words, the Expand subsystem automatically reduces the number of transmit
and read buffers available to fit within 64K words.
The size of each frame buffer is determined by the maximum size assigned to the
PATHBLOCKBYTES, PATHPACKETBYTES, and FRAMESIZE modifiers. Frame
buffers are a minimum of 1024 bytes and a maximum of 4095 bytes, or 9180 bytes in
the case of Expand-over-IP or Expand-over-ATM.
Buffer Pool
A buffer pool space of 1024 pages (2 megabytes) is allocated by default. The buffer
pool is used by the Expand line-handler process to buffer incoming and outgoing
messages while they are sent and received from the line buffer. Figure 18-13,
Figure 18-14, and Figure 18-15 show when the buffer pool is used.
Note. You can also control the frame buffer size by setting the FRAMESIZE or
PATHBLOCKBYTES modifier. However, the FRAMESIZE modifier value must be the same at
each node in the network. For this reason, you must not modify the FRAMESIZE modifier
value on a per-node basis.