SNAP-IPDLC

Summary

SNAP-IPDLC is an implementation of the "Native IPDLC" protocols specified by APPN Option set 2009. This is a "light and fast" DLC layer that allows SNAP APPN to communicate with other SNA nodes over an IP network.

The key features supported by SNAP-IPDLC include:

  • Low-occupancy, high-performance DLC code written specifically for SNAP APPN.
  • Cleanly layered architecture, using tightly specified signal-passing interfaces.
  • Full support for APPN Option set 2006, LDLC.
  • Full support for the optional LDLC liveness protocols.
  • Support for the extensions to the LDLC liveness protocol, to allow "Short Hold Mode" operation.
  • Use of UDP port numbers and IP precedence bits to ensure routing by COS.
  • Configurable UDP port numbers and IP precedence settings.
  • Fully portable core code implementation using the N-BASE, independent of operating system or underlying IP stack.
  • Fault-tolerant implementation using N-BASE buffer management utilties to recover cleanly from critical congestion.
  • A sample multi-threading Sockets UDP stub for Windows NT.
  • Downward credit mechanism to regulate data sending, allowing the HPR ARB algorithms to achieve steady, high throughput.
  • Advanced diagnostics including error logs, extensive tracing, dump facilities, SNA MS-compliant alert generation.
  • Consistent, fully-commented, C coding throughout.
  • A complete set of component test scripts.

To make use of SNAP-IPDLC, SNAP APPN must be configured to support Control Flows over RTP Tower (APPN Option Set 1402) and Native IPDLC connection network support (APPN Option set 2010).


Portability

SNAP-IPDLC is fully portable and makes minimal assuptions about the underlying hardware, operating system, or IP stack. This portability is achieved using a lightweight mapping layer, called the N-BASE, to provide services such as scheduling and memory management. SNAP APPN, SNAP-IPDLC and the UDP stub communicate using N-BASE signals to pass control information and data. The interface to the IP stack is abstracted as the SNAPS UDP interface - the UDP stub handles all processing specific to the actual IP stack being used.

SNAP-IPDLC in context with SNAP-APPN and the UDP stub
SNAP-IPDLC in context with SNAP APPN


Frames Supported

IPDLCs are required to use a subset of the Logical Link Controller (LLC) protocols defined in the International Standard ISO 8802.2. The only frames sent and received are:

  • DISC/DM
  • TEST
  • XID
  • UI


SNAP-IPDLC Deliverables

SNAP-IPDLC is delivered as a set of C source modules. The delivered code is as follows:

  • SNAP-IPDLC product code (3,200 lines of code)
  • SNAP-LDLC product code (2,700 lines of code)
  • A sample Sockets UDP stub for Windows NT (850 lines of code)

This DLC code is written solely for the use of SNAP APPN in an N-BASE, which you must port to your environment. A set of test scripts is also provided, written to run in the N-BASE testbed.

The following documentation accompanies SNAP-IPDLC.

  • UDP Stub API Interface Specification
  • Problem Determination Guide
  • Architecture Guide

For more information about SNAP-IPDLC, contact .