Meaning of "DLCST UPSN" in a SNA Server Data Link Control Trace (139594)

SUMMARY

A special mechanism is used to track SDLC statistics in the SDLC link service. The generation of statistics is controlled by byte dataru[s+27] in the Open(LINK) request messages. An Open (LINK) request message flows between the SNA Server service and each link service whenever the SNA Server service initializes. Its basic purpose it to set the link characteristics. The dataru[s+27] byte is defined by the SNA Device Interface Specification (SNADIS) as "reserved", and causes the Microsoft written SDLC link services to generate statistic messages when set to x01. Link services written by IHVs will ignore this byte, and therefor, not log these link statistics in a trace.

The following trace excerpt may appear in an SNA Server Data Link Control trace. This trace represents messages that flow between the SNA Server service and the underlying link services:

   ...
   DLC    04161000->01110101 DLCST UPSN
   DLC                       UPTYPE:3 UPCNTR:7 COUNT:0
   ...
				

The definitions of the UPTYPE and UPCNTR fields are as follows. The COUNT field is not used.

UPTYPE              UPCNTR
==========================

Type 1
             1 Number of Test cmds rcvd
                  2 Number of Test rsps sent

Type 3
                  1 Non productive receive timeout
                  2 Idle Timeout
                  3 Write retry
                  4 Receiver character overrun
                  5 Transmitter underrun
                  6 Connection problem
                  7 FCS error
                  8 Primary station abort received
                  9 SDLC Command reject
                 10 DCE error
                 11 Write timeout
                 12 Not used
                 13 I-frame received out of sequence
                 14 I-frame discarded (primary)
                 15 No response timeout (primary)
                 16 Remote busy timeout (primary)
				

Because the trace excerpt has UPTYPE = 3 and UPCNTR = 7, the observer of the trace could conclude that this is an FCS (Frame Check Sequence) error detected by the link service.

For SNA Server 4.0 this information is located in the SDK documentation. The SDK documentation is a component that you can install with the SNA Server Setup program. By default, this documentation is installed in the Online Books for Host Integration Server 2000. To find the Open(Link) Request format, do the following:

1. On the Start menu, run the SDK Documentation for SNA or the Online Books for Host Integration Server 2000.
2. Expand SNA Device Interface Specification. (For Host Integration Server 2000, you must expand Developer's Guide before you see this.)
3. Expand Reference.
4. Expand Message Formats.
5. Expand Open(LINK), and then click Open(LINK) Request.