RFC 2166 (rfc2166) - Page 3 of 34
APPN Implementer's Workshop Closed Pages Document DLSw v2
Alternative Format: Original Text Document
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