Interpreting SNA Server API Traces: Byte Packing Considerations

 Last reviewed: April 17, 1997
Article ID: Q130593
The information in this article applies to:
  • Microsoft SNA Server for Windows NT, versions 2.0, 2.1, 2.11, and 3.0

SUMMARY

When interpreting Verb Control Blocks (VCB) within SNA Server API traces, the interpreter must consider the packing alignment of each structure. The packing depends on the #include file used to build the application. The standard SNA API include files shipped with SNA Server perform the packing of the VCB depending on whether the program is built using Win16 or Win32.

MORE INFORMATION

Sample VCB STRUCTURE for TP_STARTED APPC API verb: 

   TP_STARTED
     opcode         unsigned short int   (WORD (2 Bytes))
     opext          unsigned char        (BYTE)
     reserv2        unsigned char        (BYTE)
     primary_rc     unsigned short int   (WORD (2 Bytes))
     secondary_rc   unsigned long int    (DWORD (4 Bytes))
     lu_alias       unsigned char[8]     (8 bytes)
     tp_id          unsigned char[8]     (8 bytes)
     tp_name        unsigned char[64]    (64 bytes)

WIN32

With Windows NT (32-bit) compilations, VCBs are not packed. As a result, both DWORDs and WORDs begin on WORD boundaries, and BYTEs begin on BYTE boundaries.

The following is an excerpt from a trace taken on an SNA Server using a Win32 APPC application:

TP_STARTED response, result = PARAMETER_CHECK 

Type:Sync                                  VerbID:00001800
---- Verb Parameter Block at address 0014CBC0 ---- 
14000000 00010000 00000003 53444653     <............SDFS>
44462020 00000000 F0DE1400 D9E4D4C2     <DF  ....0...RUMB>
C1F4F0F0 00000000 00000000 00000000     <A400............>
00000000 00000000 00000000 00000000     <................>
00000000 00000000 00000000 00000000     <................>
00000000 00000000 00000000              <............    >
Referring to the "VCB STRUCTURE for TP_STARTED APPC API verb" above, the verb control block parameters are decoded as follows for Win32: 

  opcode  = 1400
  opext   = 00
reserv2 = 00 
  primary_rc = 0001 (the subsequent two bytes "0000" are ignored)
  secondary_rc = 00000003
  lu_alias     = 53 44 46 53 44 46 20 20 ("SDFSDF  ")
  tp_id        = 00 00 00 00 F0 DE 14 00
  tp_name      = D9 E4 D4 C2 C1 F4 F0 F0 ("RUMBA400 <nulls>")

...

WIN16

With Windows 3.x (16-bit) compilations, VCBs are also not packed, but are aligned differently than Windows NT (32-bit) compilations. With Win16, DWORDs and WORDs start on WORD boundaries, and BYTEs are on BYTE boundaries.

The following is an excerpt from a trace taken on a Windows for Workgroups client using a Win16 APPC application:

... TP_STARTED response, result = PARAMETER_CHECK 

Type:Sync                                  VerbID:0000180F
---- Verb Parameter Block at address 300F:0000 ---- 
14000000 00010000 00035344 46202020     <..........SDF   >
20200F00 01004B16 DF22D9E4 D4C2C1F4     <  ....K.."RUMBA4>
F0F00000 00000000 00000000 00000000     <00..............>
00000000 00000000 00000000 00000000     <................>
00000000 00000000 00000000 00000000     <................>
00000000 00000000 0000                  <..........      >
...
For Win16, note that the secondary return code immediately follows the primary return code (omitting the two NULL bytes which separate these fields in the Win32 trace above).

Additional query words: prodsna
Keywords : kbnetwork ntprotocol snaappc snacpic snalua snaprog
Version : 2.0 2.1 2.11 3.0
Platform : WINDOWS

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Last reviewed: April 17, 1997
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