TN5250 Clients Stop Responding When TN5250 Fails to Issue RECEIVE_AND_WAIT (258252)


The information in this article applies to:

  • Microsoft SNA Server 3.0 SP1
  • Microsoft SNA Server 3.0 SP2
  • Microsoft SNA Server 3.0 SP3
  • Microsoft SNA Server 3.0 SP4
  • Microsoft SNA Server 4.0
  • Microsoft SNA Server 4.0 SP1
  • Microsoft SNA Server 4.0 SP2
  • Microsoft SNA Server 4.0 SP3
This article was previously published under Q258252

SYMPTOMS

TN5250 clients may stop responding when they are connected to an AS/400 computer through the SNA Server TN5250 server. The exact symptoms that occur with the TN5250 emulator may vary depending on the emulator being used. However, usually the emulator's keyboard is locked when it is waiting for additional data from the AS/400.

CAUSE

This problem can occur when an AS/400 sends data indicating that the TN5250 server now has direction to send, followed immediately by a REQUEST_TO_SEND. The REQUEST_TO_SEND notification is received by the TN5250 server through a TEST_RTS_AND_POST post completion before the RECEIVE_AND_WAIT verb completes with a "what_rcvd" parameter, indicating that the TN5250 server has direction to send. The TN5250 server ignores the TEST_RTS_AND_POST completion and moves into SEND state when the RECEIVE_AND_WAIT verb completes, which means that it does not issue a new RECEIVE_AND_WAIT verb. The TN5250 server is not able to receive any more data for this TN5250 session because it does not issue a new RECEIVE_AND_WAIT verb. The end result is that the TN5250 client stops responding because it is expecting to receive additional data from the AS/400.

RESOLUTION

To resolve this problem, obtain the latest service pack for SNA Server 4.0. For additional information, click the following article number to view the article in the Microsoft Knowledge Base:

215838 How to Obtain the Latest SNA Server Version 4.0 Service Pack


STATUS

Microsoft has confirmed that this is a problem in Microsoft SNA Server versions 3.0, 3.0 SP1, 3.0 SP2, 3.0 SP3, 3.0 SP4, 4.0, 4.0 SP1, 4.0 SP2, 4.0 SP3.

This problem was first corrected in SNA Server 4.0 Service Pack 4.

MORE INFORMATION

The TN5250 server has been updated so that it no longer ignores the TEST_RTS_AND_POST completion when it completes before a RECEIVE_AND_WAIT verb completes. The TN5250 server now posts a new RECEIVE_AND_WAIT verb, so that it can receive the additional data from the AS/400.

The following annotated TN5250 traces demonstrate the problem described in this article:

The following two messages were captured through TN5250 LU6.2 Message traces: 

PVI   0502E0B1->1D1F0001 LU 6.2   
PVI                      MSGID:RDAT   MSGTYP:PRFLS  
PVI   
PVI   ---- Header  at address 041B77B0, 1 elements ----
PVI   01050000 00002C00 0101FDFF 0100AE00     <......,.........>
PVI   
PVI   ---- Element at address 04BA87C4, start 13, end 22 ----
PVI   000A12A0 00000400 000C                  <..........      >

This message contains 10 bytes of data sent by an AS/400 to a TN5250 client. The AS/400 also indicates that the TN5250 server has direction to send: 

PVI   0502E0B1->1D1F0001 LU 6.2   
PVI                      MSGID:RRTS   MSGTYP:?????  
PVI   
PVI   ---- Header  at address 041B75DC, 0 elements ----
PVI   04000000 00002C00 DA010000 0100AE00     <......,.........>

This message is a REQUEST_TO_SEND notification from the AS/400. The AS/400 is notifying the TN5250 server that it has more data to send. According to the time stamps in the traces, the previous two messages were received by the TN5250 server at approximately the same time.

The following trace data was captured in matching TN5250 APPC API traces: 

APPC  TEST_RTS_AND_POST response, result = OK
APPC  
APPC  Type:Async   Method:Post   Hwnd:00000000   VerbID:000F4000
APPC  
APPC  ---- Verb Parameter Block at address 00233C70 ----
APPC  81000000 00000000 00000000 00000000     <a...............>
APPC  B0482400 A0492400 01000000 00000000     <.H$..I$.........>

The TN5250 server receives notification of the REQUEST_TO_SEND through the post-completion of an outstanding TEST_RTS_AND_POST verb. This is processed prior to the completion of the following RECEIVE_AND_WAIT verb: 

APPC  RECEIVE_AND_WAIT request
APPC  
APPC  Type:Async   Method:CB     Addr:0102AAA1   VerbID:00154000
APPC  
APPC  ---- Verb Parameter Block at address 00233D0C ----
APPC  0B000000 00000000 00000000 00000000     <................>
APPC  B0482400 A0492400 00000101 00000010     <.H$..I$.........>
APPC  00000000 74453101 00000000 00000000     <....tE1.........>
APPC  

APPC  RECEIVE_AND_WAIT response, result = OK
APPC  
APPC  Type:Async   Method:CB     Addr:0102AAA1   VerbID:00154000
APPC  
APPC  ---- Verb Parameter Block at address 00233D0C ----
APPC  0B000000 00000000 00000000 00000000     <................>
APPC  B0482400 A0492400 01020101 00000010     <.H$..I$.........>
APPC  0A000000 74453101 00000000 00000000     <....tE1.........>
APPC  ---- Data at address 01314574 ----
APPC  000A12A0 00000400 000C                  <..........      >

The RECEIVE_AND_WAIT verb completes as the 10 bytes of data from the AS/400 is received.

At this point, the TN5250 server ignores the post completion of an outstanding TEST_RTS_AND_POST verb. Under normal circumstances, a new RECEIVE_AND_WAIT verb is issued when a TEST_RTS_AND_POST post completion occurs. In this case, the TN5250 server does not post a new RECEIVE_AND_WAIT, therefore it is unable to receive any additional data from the AS/400 over this session because the TN5250 server is now in a SEND state due to the completion of the previous RECEIVE_AND_WAIT.

Modification Type:MajorLast Reviewed:6/24/2004
Keywords:kbbug kbfix kbQFE kbSNA400PreSP4fix kbSNA400sp4fix KB258252
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