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A mode
specifies a set of characteristics that a local LU (LU type 6.2)
uses to communicate with its partner LU. These characteristics include
information about the way data is transmitted between the two LUs
(such as maximum RU lengths and pacing window sizes), and about
whether the LUs can establish parallel sessions. In addition, you may need to specify requirements for the
communication path between the LUs, such as enforcing a certain
level of network security, minimizing transmission time, or avoiding
the use of expensive communication links. You can define these requirements
using a class of service (COS),
which specifies minimum and maximum acceptable values for characteristics
such as transmission time, transmission cost, and network security.
The COS also specifies weightings associated with different ranges
of these values. This enables the node to calculate the best route
across the network when two or more routes to the same remote LU
are available. You do not need to associate a COS with the mode; the COS
name is determined dynamically. SNA defines a number of standard modes and associated COSs
that cover the requirements of most systems; you generally do not
need to define additional modes and COSs. You need to define
a mode only if the required mode is not one of the predefined standard
modes, which can be viewed in the Modes window. The default mode is used if the mode name in an incoming conversation
is unrecognized. If you do not specify a default mode, the default
mode is the blank mode name. The
standard mode names and their associated COS names are shown in
Table 7-1 “Standard Mode and COS Names” For more information
about the parameters associated with these standard names, refer
to the IBM SNA manuals LU 6.2 Reference-Peer Protocols
(for modes) and APPN Architecture Reference
(for COSs). Table 7-1 Standard Mode and COS Names | Mode
Name | Associated
COS Name | Purpose |
|---|
| (blank) | #CONNECT | Sessions
that do not specify a mode name (basic default COS parameters) | | #BATCH | #BATCH | Sessions
used by batch-processing applications | | #INTER | #INTER | Sessions
used by interactive applications | | #BATCHSC | #BATCHSC | Sessions
used by batch-processing applications, with a minimal level of routing
security | | #INTERSC | #INTERSC | Sessions
used by interactive applications, with a minimal level of routing
security | | SNASVCMG | SNASVCMG | CNOS (change
number of sessions) and management services sessions | | CPSVCMG | CPSVCMG | CP-CP sessions
between nodes | | CPSVRMGR | CPSVRMGR | CP-CP sessions
used for dependent LU requester (DLUR) | | QPCSUPP | #CONNECT | Sessions
used for 5250 emulation |
Once a mode has been configured, it can be used by any APPC
or CPI-C application to activate a session between a local LU and
a partner LU. An APPC application must specify the mode to use,
but a CPI-C application can use CPI-C side information (which includes
the mode name). For more information about configuring CPI-C side
information, see “Defining CPI-C Side Information”. To configure a mode or class of service, use one
of the following methods: - Motif
administration program
Select APPC and Modes from the Services menu on
the Node window, then choose New on the Mode window. - Command-line administration program
To define a mode, issue the
following command: define_mode To change the default mode, issue the following command: define_defaults To define a class of service, issue the following command: define_cos
Mode Configuration
Parameters | |
The following parameters are required for mode configuration: - Name
The
name of the mode you are defining. The mode name is a string of
1-8 characters. APPC applications that use this mode, including both local
and remote applications, may also use this name, so check the name
with your application developer (or refer to your product documentation
for a third-party application). - Session limits
Use the following fields to specify session limits: - Initial session limit
The maximum number of sessions
(up to the maximum session limit) that a pair of LUs can have using
this mode, unless a different maximum is negotiated using CNOS. Normally, use the value 8
for this field. If you are in doubt, consult your SNA network planner
or APPC application developer (or for a third-party application,
the product documentation). - Maximum session limit
The maximum number of sessions
(up to 32,767) permitted between a pair of LUs using this mode,
even with CNOS negotiation. This field is usually set to the same value as the initial
session limit. If you are in doubt, consult your SNA network planner
or APPC application developer (or for a third-party application,
the product documentation). - Minimum contention winner sessions
The number of sessions
(up to the session limit) that SNAplus2 must reserve for use by
the local LU as the contention winner. This field can usually safely be set to 0,
but if you are not sure, consult your SNA network planner. The sum of the minimum contention winner sessions and the
minimum contention loser sessions must not exceed the initial session
limit. - Minimum contention loser sessions
The minimum number
of sessions that SNAplus2 must reserve for use by the local LU as
the contention loser. Together with the value in the Minimum contention winner sessions
field, this value determines how to resolve contention for a session. This can usually safely be set to 0,
but if you are not sure, consult your SNA network planner. The sum of the minimum contention winner sessions and the
minimum contention loser sessions must not exceed the initial session
limit. - Auto-activated sessions
The number of sessions (up to the
minimum contention winner count) that are automatically activated
after CNOS negotiation has taken place for a session between a local
LU and partner LU using this mode. Specifying a value for this field
enables an LU that uses this mode to start sessions automatically
in response to a request from a TP for a conversation to be allocated
immediately.
- Receive pacing window
Use these fields to specify
how many RUs can be received before an SNA pacing response is sent: - Initial window size
The initial setting for the number
of request units (RUs) that the local LU can
receive before it must send a pacing response to the remote LU.
This can be safely set to 4. Setting it higher can improve performance in some circumstances,
but doing so also increases memory usage. - Maximum window size
The maximum number of request
units
(RUs) that the local LU can receive before it must send a pacing
response to the remote LU. This value is optional. If it is not supplied, the maximum
receive pacing window is unlimited. If a value is supplied, it is
used to limit the size of the receive pacing window for adaptive
pacing adaptive pacing . If adaptive pacing is not used, this value
is ignored.
The pacing window can be from 0
through 32767 bytes. A value
of 0 specifies an unlimited
window. If the adjacent node supports only fixed pacing, these values
determine the fixed-pacing window size; but the adjacent node can
still set a window size through negotiation. If the adjacent node
uses adaptive pacing, these values set the initial window size. - Session timeout
The number of seconds (0 - 65535)
that an LU 6.2 session using this mode must be inactive before it
can time out. Changing this value affects only sessions that are
activated using this definition (not sessions that are already active). If you use a value of 0,
sessions are timed out as soon as they become free. - Maximum RU size
A range that determines how much data
is buffered before being sent to the partner LU. The upper limit can be from 256
through 62440 bytes. You can
safely set the upper limit to 1024
bytes. Setting it higher can improve performance in some circumstances,
but doing so also increases memory usage. The lower limit can be 0 or a value from 256 through the upper
limit you specify. If the value in this field is different from the RU size defined
for the remote node, the size used for a session with that node
can be negotiated to establish an appropriate RU size for the session.
The actual value cannot be lower than the lower limit field. These numbers, together with the send and receive pacing values,
can be used to tune the session-level throughput between the local
and partner LUs. If you do not know what values to use, start with
the default values and adjust them as needed to maximize throughput. - Reset
to SNA defined values
If you are modifying
a standard mode using the Motif dialog, you can click on this button
to reset the values of the mode parameters to the SNA-defined values.
Additional Configuration | |
After performing the
mode configuration, continue with the following configuration tasks: |
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