Browse Prior Art Database

Network Device Interface Specification Loopback Device Driver to Support SNA Over a PS/2 Channel

IP.com Disclosure Number: IPCOM000106096D
Original Publication Date: 1993-Sep-01
Included in the Prior Art Database: 2005-Mar-20
Document File: 4 page(s) / 138K

Publishing Venue

IBM

Related People

Baldiga, FP: AUTHOR

Abstract

A method to enable OS/2* Communications Manager (CM) applications (3270 Emulation, APPC) to communicate over a parallel channel interface to a S/370 or S/390 host via SNA protocols. A PS/2* personal computer utilizes the MICRO CHANNEL* bus to Mainframe Connection adapter (formerly PCA) to connect to the parallel channel. The programs are supported on OS/2 1.3 and OS/2 2.0. Existing applications such as APPC require no modifications.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 51% of the total text.

Network Device Interface Specification Loopback Device Driver to Support SNA Over a PS/2 Channel

      A method to enable OS/2* Communications Manager (CM)
applications (3270 Emulation, APPC) to communicate over a parallel
channel interface to a S/370 or S/390 host via SNA protocols.  A
PS/2* personal computer utilizes the MICRO CHANNEL* bus to Mainframe
Connection adapter (formerly PCA) to connect to the parallel channel.
The programs are supported on OS/2 1.3 and OS/2 2.0.  Existing
applications such as APPC require no modifications.

These features of LAN protocols are critical to the solution:

1.  A LAN adapter can be shared by multiple protocols such as 802.2
    or Netbios.  This allows multiple applications to communicate
    through the same adapter on a LAN.  One way sharing occurs is
    through the use of unique service access points (SAPs) on the
    adapter.  A SAP is a way of distinguishing between the different
    users of an adapter.  For example, an 802.2 application can open
    SAP 8 on a token-ring adapter.  Another 802.2 application could
    open SAP 4 on the same adapter and they could communicate to

    different remote computers.  If they opened different SAPs but
    specified the same source and destination address the two
    applications could communicate with each other on the same
    computer.

2.  The second feature is the support of Network Device Interface
    Specification (NDIS) in OS/2 Extended Services.  NDIS is an
    architected interface for LAN adapter device drivers and protocol
    drivers.  It allows upper-layer protocols to utilize an adapter
    by communicating to the device driver via the NDIS interface.
    Thus, a new adapter can be introduced and supported by the
    protocol driver without modification of the upper layers of
    software.  The adapter and device driver are only concerned with
    sending and receiving frames.  The protocol driver keeps track of
    the SAPs and applications using the SAPs.  They communicate with
    each other via the NDIS interface.

3.  A loopback feature typically exists in LAN adapters such as
    token-ring to wrap or loopback frames back to upper layer
    protocols.  The protocol driver passes a frame to the adapter
    driver to be sent on the LAN.  The adapter gets the frame from
    the adapter driver and immediately returns it as a received
    frame.  The loopback feature is often used to allow two
    applications to communicate to each other in the same computer.
    Each application would open a different SAP.  The source and
    destination LAN address would of course be the same.  Programmers
    often use loopback features to test out client/server or
    cooperative applications on the desktop before moving them to a
    LAN environment.  The disadvantage to using the loopback feature
    of an adapter, however, is...