Chapter 3. Operating NetView FTP V2.2.1 MVS - IBM

Pacing
How Pacing Affects Throughput
Pacing, as specified for the VPACING operand of the ACF/VTAM APPL definition
statement, can have a considerable effect on throughput. However, the best value
for pacing is difficult to calculate with precision, because you can alter both RU size
and pacing to affect the throughput.
A small RU size and a pacing value of one causes the least effect on other components
of the network, but gives the slowest throughput. Conversely, a large RU
size and a large pacing value have a greater effect, but give the best performance
(assuming the ACF/NCP/VS or ACF/VTAM components can handle the volume of
data). Often the best values are probably intermediate values, unless the installation
has special requirements.
For customization and tuning, start with a VPACING value of 4.
Negative impacts of no pacing or a large pacing window are:
� Severe ACF/VTAM buffer problems could occur.
� The buffers of the LU and the intermediate routing nodes could overflow.
� More system storage must be reserved for each session.
On links where SNA class-of-service is used, you can adjust this parameter. If
pacing is not used, severe ACF/VTAM buffer problems might occur.
Pacing Specifications
Pacing specifications can be particularly important when controlling the flow of data
in a network, especially to avoid a Network Control Program (ACF/NCP/VS) “slow
down.” The following explanations are useful when defining pacing values for the
NetView FTP V2.2.1 MVS BIND image in the logon mode table entry:
PSNDPAC and SRCVPAC are Zero
The value of VPACING from the APPL is used. If the NetView FTP
V2.2.1 MVS sending server is the primary LU, VPACING controls
pacing.
PSNDPAC and SRCVPAC are Nonzero
The values are unchanged, that is, VPACING is not used. If the
NetView FTP V2.2.1 MVS sending server is the primary LU, the value
in the BIND, not VPACING, controls pacing.
SSNDPAC is Zero
The values are unchanged, that is, VPACING is not used. If the
NetView FTP V2.2.1 MVS sending server is the secondary LU, the
value in the BIND image, not VPACING, controls pacing. In other
words, there is no pacing. This might cause severe buffer problems in
ACF/VTAM.
SSNDPAC is Nonzero
The value of VPACING from the APPL is used. If the NetView FTP
V2.2.1 MVS sending server is the secondary LU, VPACING controls
pacing.
Appendix E. Factors That Affect the Performance of NetView FTP V2.2.1 MVS 213