HCON Display Session Pooling

Pooling is a method for partitioning resources to ensure a logical distribution of the workload. Managing HCON display session pooling, includes:

• DFT pooling
• HIA pooling
• SNA Node T2.1 pooling
• Configuration of SNA T2.1 sessions with multiple pools
• Setting up an SNA Node T2.1 LU pools
• LU pooling management

Introduction to Pooling

Pools are formulated based on:

• Hardware adapters
• A collection of logical units (LUs) based on departmental requirements
• Connectivity to the host
• Host transaction application environment
• Type or frequency of usage

When an HCON session is initiated, an available session from the pool is used. When the session ends, the session is returned to the pool. Session pooling applies to display sessions only. Session pooling support is available for these connectivity types:

• Distributed Function Terminal (DFT)
• Host Interface Adapter (HIA)
• SNA Node T2.1

DFT and HIA pools are automatically defined based on the adapter name. SNA Node T2.1 pools must be defined by using the SNA SMIT Configure LU Profiles for 3270 Communication option.

HCON DFT Pooling

The DFT Session Configuration and Adapter Relationship figure shows the logical relationship between a display session, 3270 coax adapters, and session resources.

These restrictions apply to DFT pooling:

• The controller, configured through control unit customization, defines the number of sessions available on a given coax port. The controller allows up to five sessions per port.
• The Virtual Telecommunications Access Method/Network Control Program (VTAM/NCP) defines the session type, display or printer, for each session. The host definition and session profile must have the same session type configuration.

SNA DFT

Only display sessions are supported for SNA DFT. All sessions are available to defined users. According to the pooling principle, each 3270 connection adapter is an LU pool. The LUs are assigned by the first available, lowest address. All users are pooled within the same adapter. The emulator issues an error message if a user attempts to start a session when the resource is not available.

Non-SNA DFT

For non-SNA DFT sessions, the principle is the same as for SNA DFT sessions except printer sessions are ignored.

Note: The 3270 Connection Adapter must be configured with the printer address so that printer sessions can be detected and bypassed.

HIA Pooling

Only display sessions are supported for Host Interface Adapter (HIA) connectivity. All sessions are available to defined users. According to the pooling principle, HIA is a pool. The sessions are assigned by the first available, lowest address. All users are pooled within the same adapter. The emulator issues an error message if a user attempts to start a session when the resource is not available.

SNA Node T2.1 Pooling

Guidelines for using SNA Node T2.1 pooling pertain to:

• Pooling support
  • Only display (LU type 2) sessions are pooled.
  • LUs can be grouped into different resource pools.
  • SMIT provides configuration support through the Configure LU Profiles for 3270 Communication option, where LU pools are generated.
  • SMIT displays LU pool statistics and specific LU pool information using the Control options for HCON.
• Pooling principle
  • LU assignments are performed on a last in, first out (LIFO) strategy that uses LUs exhibiting stability.
  • After eight consecutive failed attempts to activate an LU, the LU is disabled and removed from further consideration until all sessions using the pool are terminated.
  • Disabled LUs are recycled either after all available LUs are tried or after all sessions using a pool are terminated.
• Host VTAM/NCP information affecting pooling availability
  • The host VTAM/NCP definition determines the number of LUs within a physical unit.
  • The LU type (type 2 for display, or types 1 and 3 for printer sessions) is defined from the host's VTAM/NCP definition. The host's VTAM/NCP definition determines the LU type 2 sessions available for pooling use.
• Usability characteristics
  • The SNA Logical Connection Profile name selected from the pool can be displayed within { } (braces) in the Session Use field of the Operator Information Area (OIA). The SNA profile name shares the same area with the Session Use characteristic defined in the HCON session profile. The SNA profile name appears only if a session is available and if sufficient space in the Session Use field is available. The SNA profile name is useful during problem determination.

    To ensure the SNA Logical Connection Profile name is displayed in the Session Use field, limit the length of both fields or the Prefix characteristic. To calculate a workable length for the Session Use field, subtract the length of the SNA Logical Connection Profile name from 15. For example, if the RVLTN320 pool is being used (8 characters), Session Use should not exceed 7 characters.

    Note: As a general guide, use only 10 characters for the Session Use field and 5 characters for the SNA Logical Connection Profile or Prefix field. These are recommended lengths. The actual maximum lengths are:

    Field	Max Length
    Session Use	20 characters
    SNA Logical Connection  or Prefix
    	12 characters

  • If an LU is not available in the defined pool, an error message displays or writes to the $HOME/hconerrors file.

Configuration of SNA T2.1 Sessions with Multiple Pools

The SNA T2.1 Session Configuration and SNA Profile Relationship figure shows the relationship between multiple HCON users with multiple pools of SNA Logical Connection profiles. All users are configured with a single SNA Attachment Profile (SDLC) for a given communication adapter.

Setting Up an SNA Node T2.1 LU Pool

In working with an SNA Node T2.1 pool, you must enable and disable SNA Node T2.1 display session pooling.

Enable SNA Node T2.1 Display Session Pooling

1. Obtain the required host information from the host system programmer, including:
   • Device attachment information
   • LU address range
   • LU type of each address
2. Create the SNA Attachment Profile that operates with these characteristics.

   Note: You have the option to create the SNA Attachment Profile before or during the Quick Configuration.

3. Partition the LUs into one or more pools based on the LU address range provided and the operating environment.
4. Define each pool using the Configure LU Profiles for 3270 Communication option in SMIT. The LU pool name is represented by its LU Profile Prefix.

   Note: It is not advisable to use a : (colon) when entering information into SMIT text-entry fields. SMIT interprets a : (colon) as a field delimiter.

5. Assign each HCON user's session to a pool based on the session profile and the user's requirements. HCON does not verify that the pool exists during the configuration process.

   Note: An * (asterisk) at the end of the pool name indicates that pooling occurs within the defined pool.

The LU Prefix Example for Pooling figure shows the Quick Configuration process to create POOL1, POOL2, POOL3, and POOL4.

Disable SNA Node T2.1 Display Session Pooling

To disable pooling support for a session, use the entire SNA Logical Connection Profile name. The entire profile name must be entered because the prefix and * (asterisk) value are only used to enable pooling.

Use these examples of LU prefix values in the SNA Logical Connection Prefix or Profile field:

LU Pooling Management

The stathcon command and the HCON Control option in SMIT are available for LU pooling management. The stathcon command lists the status of HCON session profiles and SNA logical unit (LU) pools. The HCON Control option in SMIT is useful for administering host resources and balancing the load between user needs and system requirements.

To manage LU pooling you can:

• Monitor specific LU pools during peak periods to ensure fair distribution.
• Reassign LU pools with low usage to other pools. The reassignment process requires restarting the SNA subsystem.
• Display the status of each LU within a pool for session management and host problem determination.
• Identify congested pools.
• Perform pool assignment by using the sna3270lu command in a SMIT shell script (see SNA documentation for more information).