Unable to Activate Multiple DLS Connections Using the Same SAP (180938)

CAUSE

An 802.2 Data Link Control (DLC) link services can support up to 128 connections over a particular Local SAP. The number of connections that can be configured over using the same Local SAP will depend on the remote MAC/SAP addresses the connections are configured to connect to.

When a DLC Link Service is initialized, DLC issues a DLC.OPEN.SAP command to activate a SAP and reserve a number of link stations for that SAP. The DLC Link Service is not designed to dynamically allocate additional link stations after is SAP is opened, therefore it cannot allocate additional link stations if the original allocation did not reserve enough to support all of the configured connections for a particular SAP.

The problem described in the SYMPTOMS section can occur in a DLS environment because the "Central" SNA Server that opens the SAPs for the distributed 802.2 DLC link service does not know how many connections will be using the link service. If the original allocation of link stations is not sufficient to support the number of connections that will be using a SAP, some of the configured connections using that SAP will not activate and will stay in a "Pending" state.

STATUS

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section of this article. This problem was corrected in the latest SNA Server versions 3.0 and 4.0 U.S. Service Packs. For information on obtaining these Service Packs, query on the following word in the Microsoft Knowledge Base (without the spaces):

S E R V P A C K

MORE INFORMATION

The hotfix modified the DLC Link Service so that it uses the DLC_REALLOCATE command to dynamically allocate more link stations after the DLC.OPEN.SAP command has been issued if they are needed. Another enhancement was made to the DLC Link Service so that it no longer allocates a SAP buffer pool for every SAP that is opened. By default, Windows NT DLC does not use SAP buffer pools. This change saves a maximum of 64 KB of memory per opened SAP.

Note The update DLC Link service has to be applied to the "Central" SNA Server.

Steps to Reproduce This Problem

Have three SNA devices available to establish connections to (this can be any combination of Hosts, AS/400 or SNA Servers).
Set up a "Central" SNA Server site with one 802.2 DLC Link Service configured with the "Allowed to be distributed" option selected and the "Use Fixed SAP" option deselected.
Set up a "Remote" SNA Server site with one Distributed Link Service configured to use the link defined on the "Central" site in Step 2.
On the "Remote" site configure three connections using the same Local SAP on the same SnaRemX link service but to three different SNA devices (MAC addresses).
Activate the connections one at a time. The first two will go to an Active state and the last one will stay in a Pending state.
Stop one of the Active connections, and the Pending connection activate.

This can be reproduced the same way with two connections configured on the "Remote" SNA Server and one local connection on the "Central" SNA Server.

Note There may be cases when more than two connections using the same Local SAP can be started before the next connection fails to activate. This will depend on how the "Central" SNA Server is configured.

This problem does not occur if the distributed 802.2 link service is configured with the "Use Fixed SAP" option enabled.