IBM Communication Controller Migration Guide

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,

SG24-4656

򐂰 Subarea to APPN Migration: HPR and DLUR Implementation, SG24-5204

򐂰 Inside APPN - The Essential Guide to the Next-Generation SNA,

SG24-3669

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