SNAP-LLC2

Summary

SNAP-LLC2 is a full implementation of a Class II Logical Link Controller (LLC) based on International Standard ISO 8802-2. The key features supported by SNAP-LLC2 include:

  • Type I and Type II LLC communication
  • a DLC layer for SNA LAN communications (including XID and TEST retries)
  • a layered architecture allowing use of just the 'pure' LLC layer of a full DLC/LLC stack
  • two-way credit based flow control for I-frames between the application and SNAP-LLC2
  • provision of IBM's Dynamic Window Algorithm for controlled restart of I-FRAME traffic after LAN congestion
  • promiscuous access to the underlying LANs for router-type applications such as DLSw
  • Token Ring and Ethernet
    • Token Ring source routing
    • auto-sensing of 802.3/DIX2 Ethernet formats by Link Station
  • Frame Relay, RFC1490
  • flexible dynamic configuration capabilities
  • advanced diagnostics (error logs, tracing, dumps and SNA alert generation)
  • C coding throughout.

SNAP-LLC2 is fully portable and makes very few assumptions about the underlying hardware or operating system. This portability is achieved by using a mapping layer, called the N-BASE, that provides services such as scheduling and memory management.

Both SNAP-LLC2 and the N-BASE have been designed to perform well in both standard multi-threaded, single processor operating systems as well as more complex environments such as:

  • ultra high-performance single-threaded operating systems or sub-systems found at the heart of most router products
  • distributed environments with small high-speed data path processes and larger background management processes
  • symmetric or asymmetric multi-processor systems.


Compatibility

SNAP-LLC2 interoperates with SNAP APPN. Both products make use of the N-BASE operating environment. They communicate over the SNAPS DLC interface using N-BASE signals to pass information.

SNAP-LLC2 communicates with a MAC Stub over the MAC interface. The MAC Stub interacts closely with the MAC level device driver which interfaces to the LAN card.

SNAP-LLC2 in context with SNAP APPN

SNAP-LLC2 interoperates with SNAP-DLSw. They communicate over the Extended DLC interface using N-BASE signals to pass information.

SNAP-LLC2 communicates with a MAC Stub over the MAC interface. The MAC Stub interacts closely with the MAC level device driver which interfaces to the LAN card. When used by SNAP-DLSw the MAC Stubs must implement the promiscuous mode of operation.

SNAP-LLC2 in context with SNAP-DLSw


Frames Supported

For interworking with other LLC implementations, SNAP-LLC2 supports the Asynchronous Balanced Mode (ABM) commands as defined in the International Standard ISO 8802.2. These are

  • DISC/DM
  • I-FRAME
  • REJ
  • RNR
  • RR
  • SABME/UA
  • TEST
  • XID
  • FRMR
  • UI


Statistics

The statistics kept by SNAP-LLC2 include:

  • counts of each frame type
  • count of bytes sent in each frame type
  • error counts
  • Token Ring routing data.


SNAP-LLC2 Deliverables

SNAP-LLC2 is delivered as a set of C source modules. The delivered code is as follows:

  • SNAP-LLC2 product code (14,500 lines of code)
  • Sample MAC Stub (1000 lines of code)
  • SNAPS Product Support Library (4,500 lines of code)
  • Sample N-BASE (7,500 lines of code).

A set of test scripts is also provided. The scripts are written to run in the N-BASE testbed which you must also port to your environment. All of the tests run in the sample portable N-BASE, which contains a testbed.

The following documents accompany SNAP-LLC2 version 1.1.

  • LLC Interface Specification
  • MAC Interface Specification
  • Problem Determination Guide
  • Architecture Guide
  • Product Overview

For more information about SNAP-LLC2 contact .