OOBPLUS - CompuServe B protocol objects
                     Copyright (c) Steve Sneed 1991
                           All rights reserved


   The CompuServe Information Service (CIS) is the largest and most
popular system of its type in the world, with over 1,000,000 members
in the US and abroad.  CIS provides several "special" capabilities,
such as the ability to display graphics in real time and the ability
to encapsulate the entire online session within a protocol for
improved data integrity and management. Many of these special
capabilities are based on CompuServe's own transport protocol,
the "B" protocol.  Because of the size and number of users of CIS
today, any communications program should provide support for at least
the basic File Transfer Protocol (FTP) portions of the B protocol.
OOBPLUS makes providing that support simple.

   The OOBPLUS unit provides a set of objects for B protocol.
Derived from Async Professional's AbstractProtocol object, OOBPLUS
provides a "plug-in" interface for both the B series protocol's FTP
services, and the special version for use with CompuServe's GIF
graphics image display services.

   There are three distinct species of B protocol in use today:

"Classic" B: The original B protocol. This version defines a protocol
similar in some ways to the XMODEM protocol but with special
consideration for the packet-switcher network CIS uses to connect
users to their hosts.

"Quick" B: Quick B (QB) is a major enhancement over Classic B.
While maintaining backwards compatibility with Classic B it adds
"send-ahead" technology (the ability to send more than one packet
before receiving an acknowledgement), a larger 1K packet size for
better thruput with higher speed modems, and 16-bit CRC blockchecking.

"BPlus": BPlus (B+) is a superset of QB, or more correctly, QB is a
subset of B+.

   B+ is not a file transfer protocol in the typical sense.  It is a
"Transport Level" protocol, and as such can be used to provide protocol
error trapping and data management to an entire online session which may
include file transfer sub-sessions.  The full B+ specification defines
multiple "layers" of protocol support, the lowest being the "Transport
Layer".  The transport layer provides the basic data packetization, flow
control and error handling.

   HMI NOTE: This new version of OOBPLUS now specifically includes the
modifications nessessary to support the special HMI version of B+.  However,
because no documentation has been made publicly available by CompuServe on
the exact format or usage of HMI, what's here has been arrived at by
experimentation and may require modification as more information on HMI
becomes available.


   OOBPLUS implements the B protocols in a layered fashion, just as the CIS
hosts.  An abstract parent object handles the basic flow management and
packetization chores, while child objects implement the specific FTP and
GIF receive services.  A hierarchial diagram:

AbstractProtocol
  +-- (...other derived APRO protocols...)
  +-- BPProtocol             {abstract BPlus parent}
        +-- BPProtoFTP             {File Transfer services}
        +-- BPProtoGIF             {GIF receive/decode services}


OOBPLUS and GIF
---------------

   GIF data may come from a single file, the serial port, as a piece
of a file from database-type storage, etc., and may be sent to the
screen, a printer, or some other output device, so it makes sense to
isolate the process of getting the stream's raw data and outputting
the processed image data from the decoder's inner workings.
Doing so also makes implementing a GIF decoder thru a protocol much
easier.  The demo decoders' kernel (DEGIF.PAS) names two procedure
pointers, one to a function which returns the next byte of raw data
and one that does something with a processed raster line of display
data, and refers only to these proc pointers for source and
destination.  Various "shells" can then be wrapped around the decoder
to implement the routines for a particular decoder's needs.


   I can be contacted via CIS at User ID# 70007,3574. I frequent
several forums at least once a day, especially IBMCOM, PCVENB
(TurboPower's section 6), BPROGA and PICS.  The TurboPower folks
will be happy to help you as well, but to help keep their support
headaches in check I hope you'll contact me first; they may need
to forward questions to me anyway. 
US Mail will reach me at:

     Ozarks West Software
     14150 Gleneagle Dr.
     Colorado Springs, CO  80921