424 IBM Communication Controller Migration Guide
addresses that are saved by migrating to APPN and the additional low-order
addresses that are used for HPR connections (RTP PUs). Since there are
typically many more LU-LU sessions than RTP PUs, this tradeoff generally
results in fewer low-order network addresses being used after migrating from
subarea to APPN.
Migrate dependent LUs to DLUR-attachment
In the past, DLUR-served dependent PUs and LUs consumed at least as many
and in some cases even more low-order network addresses as subarea-attached
dependent PUs and LUs. However, CS for OS/390 V2R5 provided a substantial
improvement because it allows DLUR-served LUs to be pre-assigned high-order
network addresses instead. In any case, some low-order network address are
typically still required for LU-LU sessions with DLUR-served LUs (depending on
where the session partner is located). It is also important to remember that
low-order network addresses are still pre-assigned to all DLUR-served PUs.
With CS for OS/390 V2R7, DLUR-served LUs typically use even fewer low-order
addresses for LU-LU sessions, because high-order network addresses can more
often be dynamically assigned for LU-LU sessions. The use of low-order
addresses for DLUR-served LUs can be completely eliminated if the DLUS
VTAM (CS for OS/390 V2R7 or above) is configured as a pure NN. The use of
low-order addresses for DLUR-served PUs can be completely eliminated if VTAM
is at least z/OS CS V1R6.
The single greatest inhibitor to migrating subarea-attached dependent PUs and
LUs to DLUR-served PUs and LUs is the fact that at least some portion of the
network must be migrated to APPN. Additionally, migrating end users from
subarea-attached dependent LUs to DLUR-served LUs usually requires new
hardware and software (for the DLUR nodes).
Note: Subarea-to-APPN migration can be very complicated, particularly for
large, complex SNA networks. Careful planning is required to avoid running
into problems during the migration. Useful insights into planning such a
migration can be found in:
򐂰 Subarea to APPN Migration: VTAM and APPN Implementation,
򐂰 Subarea to APPN Migration: HPR and DLUR Implementation, SG24-5204
򐂰 Inside APPN - The Essential Guide to the Next-Generation SNA,
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