"SSCP Connection Already Open" error occurs when starting 257th 3270 session (288202)


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
  • Microsoft SNA Server 4.0 SP4
  • Microsoft Host Integration Server 2000
  • Microsoft Host Integration Server 2004
This article was previously published under Q288202

SYMPTOMS

SNA Server or Host Integration Server sends an "Open SSCP RSP Error" response to an emulator's request to start the 257th 3270 session that is configured to use any available resource. For example: 
FMI   ----------------------------------------------- 17:54:55.0328
FMI   01020000->16120100 OPEN  SSCP RSP ERROR
FMI                      FMI  Err1:0055 Err2:0003
FMI
FMI   ---- Header  at address 01194EA8, 2 elements ----
FMI   03010203 00010055 00030200 01000000     <.......U........>
FMI
FMI   ---- Element at address 01B85228, start 1, end 20 ----
FMI   4D324C55 30303320 00002020 20202020     <M2LU003 ..      >
FMI   20202020                                <                >
FMI
FMI   ---- Element at address 01B8C438, start 1, end 18 ----
FMI   45585452 41212066 6F722057 696E646F     <EXTRA! for Windo>
FMI   7773                                    <ws              >
NOTE: Err1:0055 indicates "SSCP Connection Already Open" and Err2:0003 indicates "Control Block / Resource Shortage".

CAUSE

This occurs because all 3270 logical units (LUs) are assigned to user groups under "configured users" rather than LU pools on the SNA Server or Host Integration Server.

Users can specify an LU and receive active sessions beyond the 256 active LUs in the group. This is because the emulator is not asking for a list of LUs for that group, but instead is asking for permission to use that particular LU.

MORE INFORMATION

The following illustrates the problem:
  1. One user group assigns more than 1,000 LUs.
  2. A client requests all available LUs for the user record (or, in some emulators, requests only those LUs that are explicitly configured).
  3. The server sends back all 1,000-plus LUs.
  4. The client processes all the LUs (even ones in use) and either picks the last LU not in use and attempts to use it or stops at some predetermined number because its internal cache cannot handle any more than what was assigned to it.
  5. The client stops processing the list of LUs when the limit is reached.
The following illustrates what would normally happen when a client requests an LU from a pool:
  1. The client sends a request to the server to see what LUs are assigned to the user.
  2. The server sends back the pool name.
  3. The client sends back the pool name, requesting an LU.
  4. Server acknowledges the pool name and sends an LU from the pool that is free.
Modification Type:MajorLast Reviewed:5/23/2005
Keywords:KB288202
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