Subject: XRF and DLUR

From: "jim (j.) cobban" <[email-masked]>
Date: Fri, 29 Sep 1995 10:33:00 -0400

Many SNA subarea networks currently depend upon XRF to provide the highest
possible availability for their mission critical applications.  However XRF
is implemented in the NCP boundary network node.  If a dependent LU is
attached through an APPN node using Dependent LU Requestor then this
functionality is not available because the LU-LU session becomes an
independent LU session.  For valid architectural reasons the NCP does not
implement XRF for independent LU sessions. 

XRF is not as critical for LU 6.2 as it is for other protocols, because of
the synch-point facilities of LU 6.2.  It is not necessary to maintain a hot
standby application in LU 6.2 because in the event of loss of
session connectivity to the active application the transaction is backed out
to the last synch point and the transaction can be resent over a new session
to the backup application.

While there is no architectural requirement that independent LU sessions use
LU 6.2, this was an implementation restriction until the addition of APPN
support in VTAM V4.2 and DLUR.  Since DLUR turns dependent (e.g. 3270)
sessions into independent LU sessions this results in
the loss of XRF functionality.  Since XRF must be implemented at the boundary
function, restoring XRF in a full APPN environment would require adding XRF
functionality to DLUR.  An additional reason for performing this function at
the DLUR is that it would permit using XRF capability to provide high
availability in the event of network outages, assuming that the XRF parallel
sessions can be made to take different routes.

I note that the only reference to XRF in the current DLUR specification is to
the absence of the XRF CV from session awareness RUs sent by DLUR.

Can we have a show of electronic "hands" to see whether this is an issue
which the AIW needs to act on, and to determine the priority which should be
applied to it.