Table of Contents
Advertisement
Appendix E. Key Data Formats and Control Blocks
System Buffers
This appendix briefly discusses the key data formats and control blocks. This is by
no means an exhaustive list of the 3708 control blocks or data blocks.
It
is a very
small subset.
System buffers are primarily used to receive traffic from an SNA host or to transmit
traffic to an SNA host. When there are insufficient buffers, the 3708 temporarily
enters "buffer slowdown." While in buffer slowdown, data traffic is not accepted
from the SNA host. SNA activations are rejected. Traffic from protocol conversion
keyboard displays may be stopped and loss of data from protocol enveloping
keyboard displays may occur.
It
is undesirable for the 3708 to enter buffer
slowdown.
The number of system buffers required to support SNA application sessions can be
lessened by the host use of SNA pacing, use of SNA definite response chains, or
end-to-end pacing.
Maximizing Available System Buffers
The actions suggested here reduce the numbers of, and sizes of, certain control
blocks and data areas which might otherwise unnecessarily use up RAM space,
thereby reducing the number of system buffers. The number of system buffers
available is a function of the 3708 configuration. The following configuration
options are suggested to increase the number of available system buffers:
1.
Exclude ports from the configuration when/if it is known which ports are never
going to be used.
2. Do not configure a port for a keyboard display-with-printer unless:
• There really is such a device.
• It
will be running in protocol conversion mode.
• Both LUs will be supported by host application(s).
The keyboard display-with-printer support provides an appearance to the SNA
host as if there were another port on the 3708 for the printer. The actual case is
that the printer is on the same port and same cable as the keyboard display
device which controls it. The keyboard display-with-printer support is intended
for the case where:
• The special support is in the device.
• The two LUs are utilized in protocol conversion mode.
3. Do not configure for Model 2 emulation unless it is used.
4. Use small receive queues versus medium or large.
5. Do not configure two SNA hosts and allow access to both for all ports unless
you really mean to do so.
Appendix E. Key Data Formats and Control Blocks
E-l
Advertisement
Table of Contents
