RFC 2166 (rfc2166) - Page 3 of 34

APPN Implementer's Workshop Closed Pages Document DLSw v2

Alternative Format: Original Text Document
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RFC 2166              APPN Implementer's Workshop             June 1997


   1. Introduction

   This document defines v2.0 of Data Link Switching (DLSw) in the form
   of a set of enhancements to RFC 1795. These enhancements are designed
   to be fully backward compatible with existing RFC 1795
   implementations. As a compatible set of enhancements to RFC 1795,
   this document does not replace or supersede RFC 1795.

   The bulk of these enhancements address scalability issues in DLSw
   v1.0.  Reason codes have also been added to the HALT_DL and
   HALT_DL_NOACK SSP messages in order to improve the diagnostic
   information available.

   Finally, the appendix to this document lists a number of
   clarifications to RFC 1795 where the implementation experience to-
   date has shown that the original RFC was ambiguous or unclear. These
   clarifications should be read alongside RFC 1795 to obtain a full
   specification of the base v1.0 DLSw standard.

2. HALT Reason codes

   RFC 1795 provides no mechanism for a DLSw to communicate to its peer
   the reason for dropping a circuit.  DLSw v2.0 adds reason code fields
   to the HALT_DL and HALT_DL_NOACK SSP messages to carry this
   information.

   The reason code is carried as 6 bytes of data after the existing SSP
   header.  The format of these bytes is as shown below.

   Byte       Description
   0-1        Generic HALT reason code in byte normal format

   2-5        Vendor-specific detailed reason code

   The generic HALT reason code takes one of the following decimal
   values (which are chosen to match the disconnect reason codes
   specified in the DLSw MIB).

   1 - Unknown error
   2 - Received DISC from end-station
   3 - Detected DLC error with end-station
   4 - Circuit-level protocol error (e.g., pacing)
   5 - Operator-initiated (mgt station or local console)

   The vendor-specific detailed reason code may take any value.






Bryant & Brittain            Informational
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