Microsoft KB Archive/196606

= APPC DLL has a hardcoded limit of 4 KB GDS data size =

Article ID: 196606

Article Last Modified on 2/22/2007

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APPLIES TO


 * Microsoft SNA Server 3.0
 * Microsoft SNA Server 2.11 Service Pack 1
 * Microsoft SNA Server 2.11 Service Pack 2
 * Microsoft SNA Server 3.0 Service Pack 4
 * Microsoft SNA Server 4.0
 * Microsoft SNA Server 3.0 Service Pack 2
 * Microsoft SNA Server 3.0 Service Pack 3
 * Microsoft SNA Server 4.0
 * Microsoft SNA Server 4.0 Service Pack 1
 * Microsoft SNA Server 4.0 Service Pack 4
 * Microsoft Host Integration Server 2000 Standard Edition
 * Microsoft Host Integration Server 2000 Service Pack 1

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This article was previously published under Q196606



SUMMARY
The IBM host will reject General Data Stream (GDS) data that is larger than the 4 KB increments hardcoded in the Appc.dll file.



MORE INFORMATION
The application writes the data message and indicates the length of the data, but the APPC .dll file formats the message into LU 6.2 data format. The data flow should be similar to the following:  The CPIC application calls CMSEND, passes a pointer to the data, and sets the send length to 8872. The CPIC .dll file calls the MC_SEND_DATA function, passes a pointer to the data, and sets the send length to 8872. The APPC .dll file formats the RU with the Logical Length size and GDS header information (to indicate LU 6.2 application data) and includes the application data (following IBM LU 6.2 data formatting specifications):

9000 12FF 

9000 

02B0



The Logical Length fields (9000, 9000, 02B0) and GDS ID (12FF) account for 8 additional bytes, making the full data sent equal to 8880 bytes.

The data is split into the RU size, and segmented within the maximum frame size (265 bytes on this Synchronous Data Link Control (SDLC) connection).

The host stack does not recognize the continuation bit, therefore, any data larger than 4 KB that is sent, is rejected.

The APPC .dll file is hardcoded to send application GDS data sizes of 4 KB.

