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Q178252: Control Unit Image Number Not Available to ESCON Link Service

Article: Q178252
Product(s): Microsoft SNA Server
Version(s): WINDOWS:3.0,3.0 SP1,3.0 SP2
Operating System(s): 
Keyword(s): 
Last Modified: 13-JUN-2001

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The information in this article applies to:

- Microsoft SNA Server, versions 3.0, 3.0 SP1, 3.0 SP2 
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SYMPTOMS
========

When implementing an ESCON channel link service (such as the Polaris ESCON
channel link service), SNA Server was not providing the control unit (CU) image
number to the link service, which significantly complicates ESCON channel link
configuration.

CAUSE
=====

SNA Server was not originally designed to return the control unit image number
to the channel link service.

STATUS
======

Microsoft has confirmed this to be a problem in SNA Server 3.0 (including SP1
and SP2). This feature has been added to SNA Server 3.0 (post SP2) and allows
the SNA Server to return the Control Unit image number in dataru[s+24] of the
Open(Link) response.

This problem was corrected in the latest SNA Server version 3.0 U.S. Service
Pack. For information on obtaining this Service Pack, query on the following
word in the Microsoft Knowledge Base (without the spaces):

  S E R V P A C K

Note that the ESCON channel link service must be written to recognize the Control
Unit image number. Contact your link service vendor to determine if this is the
case. If so, to make use of this new feature, the updated SNACFG.DLL must be
applied and the configuration file must be resaved using SNA Server Manager.

MORE INFORMATION
================

The Polaris ESCON link service version 2.14 (with the v1.12 version of the
Polaris ESCON configuration DLL) supports the ability to use the Control Unit
image number. Here is some additional background describing what the control
unit image number is used for:

The control unit image is an ESCON feature. It allows a physical control unit to
support up to 16 logical control units. The CU image corresponds to the "CUADD"
parameter in the CNTLUNIT IOCP macro or the Logical Address in HCD.

The Polaris ESCON link service supports a maximum of 250 devices over a maximum
of 16 CU images. The change to SNA Server makes it easier for customers to
configure SNA Server to use ESCON. Currently, in order to allow the customer to
use multiple CU images, the customer must configure the link service with the
devices they need on each CU image. Then they use the number in the channel
address box of the connection to specify an index into a table made from the
link service configuration. Here's an example:

Actual configuration:

  CU Image  Base Device Address  Num Devices
     0               20              4
     2               40              2
     3               20              4

Channel addresses to input into SNA Server configuration:

  Channel Address   CU Image - Device Address
       00                  0 - 20
       01                  0 - 21
       02                  0 - 22
       03                  0 - 23
       04                  2 - 41
       05                  2 - 42
       06                  3 - 20
       07                  3 - 21
       08                  3 - 22
       09                  3 - 23

This makes configuration more difficult. With this new feature, customers still
must configure the link service as before because the ESCON channel adapter
needs to know at initialization (ie. when SNA Server is started) which devices
it will be using. But in the connection properties the user can put in address
20 CU image 0 instead of just address 00 and so on.

The link service configuration has a check box which allows the user to choose to
use the new method. This is not done automatically. The link service has to be
told which of the two methods is in use since the field that contains the CU
image was 0 for old version of SNA Server, but 0 is a valid CU image.


Regarding the use of the Polaris ESCON link service, this change will not affect
users who don't want or need to change their link service configuration. They
will still be able to update the link service and driver to newer version with
having to redo any part of their configuration.

Additional query words:

======================================================================
Keywords          :  
Technology        : kbAudDeveloper kbSNAServSearch kbSNAServ300 kbSNAServ300SP1 kbSNAServ300SP2
Version           : WINDOWS:3.0,3.0 SP1,3.0 SP2
Issue type        : kbbug
Solution Type     : kbfix

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