Compression Control Feature

The Compression Control Feature (CCF) allows you to control the type of compression used between nodes, that is, standard versus extended, and how compression is used on a node, that is, whether the selected compression type is required, may be used, or is not allowed at all. This control may be forced globally by the PNODE or negotiated by the SNODE. Global compression control settings are specified in the initialization parameters, whereas settings for specific nodes are specified in the adjacent node entry for those nodes.

Because this feature overrides compression settings specified in a Process, its default settings allow both types of compression so that the Process determines the type of compression that will be used (standard “COMPRESS” or extended “COMP EXT”).

When control of compression is being exercised, the PNODE always applies its rules to the Process and then attempts negotiation. Negotiation is not performed if the other node does not have the CCF code installed. (The node having Process control is in charge in this case.)

Where a partner node also has CCF installed, then the two nodes will negotiate the type of compression that will be used. If one node says that compression must be used and the other says that it is not allowed, then the step will fail, causing an IMPASSE situation (SCPA994I). Also, if one node says FORCE EXT and the other replies FORCE STD, this is also an IMPASSE situation.

The parameters that govern compression control come from either or both the following initialization parameters and network map parameters:
  • Initialization parameters
  • Network Map parameters

The CCF initialization parameters are refreshable, so they may be changed at any time without requiring the DTF to be recycled. When you do make changes to these initialization parameters, your changes will cause global overrides to Processes on your system(s). For example, where standard compression is being used in Processes, if the initialization parameters are changed to specify COMPRESS.STD=DISALLOW, none of your Processes will use standard compression (as long as netmap overrides are disallowed or the node definition does not contain compression control keywords).

If you want to put the netmap compression control keywords into effect, you have to specify values for those keywords in the ADJACENT.NODE definitions because they do not have default values.

For example, if the netmap is changed for a node (or nodes) to specify COMPRESS.EXT=FORCE, then all Processes that run on that node will behave as if COMP EXT was specified in each COPY step.

Because of situations such as these, it is important for you to contact your partners to discuss how compression will be handled between the two IBM® Connect:Direct® systems to avoid IMPASSE copy failures.