Print Jobs May Not Finish Printing if Host Sends SHUTD (216123)

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SNA messages can be sent with two different priorities: normal and expedited. Expedited messages take precedence over other messages waiting to be sent on the same session. SHUTD and SHUTC commands are sent as expedited messages. Because SHUTD commands are sent as expedited messages, it is possible for these to be sent prior to normal messages already queued for the same session. The problem described in this article occurs when a SHUTD message is sent to SNA Server's Host Print service before some of the preceding normal messages are sent. The following is an example of how the host print data was intended to be sent and processed:

Host                           SNA Server                 Print Server
----                           ----------                 ------------
Data (Begin Bracket)  ->
                               Data (Begin Bracket)  ->
                                                     <-   Acknowledgement
                      <-       +RSP
Data                  ->
                               Data                  ->
                                                     <-   Acknowledgement
                      <-       +RSP
Data                  ->
                               Data                  ->
                                                     <-   Acknowledgement
                      <-       +RSP
Data (End Bracket)    ->
                               Data (End Bracket)    ->
                                                     <-   Acknowledgement
                      <-       +RSP
SHUTD                 ->
                               SHUTD                 ->
                      <-       SHUTD +RSP
                                                     <-   SHUTC
                      <-       SHUTC
SHUTC +RSP            ->
UNBIND                ->
				

In this case, the SHUTC is sent after the last print data as noted by the End Bracket (EB) indicator. Therefore, the entire print job completes.

The following is a sample sequence that results in only part of the print data actually being printed:

Host                           SNA Server                 Print Server
----                           ----------                 ------------
Data (Begin Bracket)  ->
                               Data (Begin Bracket)  ->
                                                     <-   Acknowledgement
                      <-       +RSP
Data                  ->
                               Data                  ->
                                                     <-   Acknowledgement
                      <-       +RSP
SHUTD                 ->
                               SHUTD                 ->
                      <-       SHUTD +RSP
                                                     <-   SHUTC
                      <-       SHUTC
SHUTC +RSP            ->
UNBIND                ->
				

In this case, the last two data messages shown in the first example above are not shown as they never reach the SNA Server. The data messages are not shown because the SHUTD/SHUTC sequence occurred before these normal data messages could be sent.

If the device (that is, IBM 3745 or Cisco Routers) that is responsible for sending the actual host messages to the SNA Server has some normal and expedited messages for the same host session, it is possible that the expedited messages will be sent prior to normal flow messages.

After applying the update, SNA Server's Host Print service can be configured so that it will not issue a SHUTC command in response to a SHUTD command until an RU with an End Bracket indicator is received. This prevents the print server from issuing the SHUTC command immediately on the receipt of the SHUTD command, which caused the problem described here.

The following Registry entry has to be configured to allow the print server to delay the SHUTC command processing.

1. Start Registry Editor (Regedt32.exe).
2. Locate the following key in the registry:
   

   
   HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SnaPrint\Parameters
     
   						

   NOTE: The above registry key is one path; it has been wrapped for readability.
3. On the Edit menu, click Add Value, and then add the following registry value:

         Value Name: SHUTCafterEB
         Data Type:  REG_SZ
         Value:      YES
     
   					

4. Quit Registry Editor.