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Q215473: XFOR: Understanding How SNADS Connector Uses LU 6.2

Article: Q215473
Product(s): Microsoft Exchange
Version(s): winnt:5.5
Operating System(s): 
Keyword(s): 
Last Modified: 22-APR-1999

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The information in this article applies to:

- Microsoft Exchange Server, version 5.5 
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SUMMARY
=======

This article provides a brief overview of SNADS, LU6.2, and APPC, and how the
SNADS Connector uses LU 6.2.

MORE INFORMATION
================

SNADS (Systems Network Architecture Distribution Services) is a network of
Distribution Service Units (DSU) that are responsible for transporting
distributions (messages) from one end-user to another end-user. SNADS (or
specifically, each DSU) uses LU 6.2 as a transport to send a distribution from
one DSU to another DSU.

LU 6.2 is a resource on an SNA node that can establish communications with
another LU 6.2 on another SNA node to pass data. LU 6.2 also exposes a
programming interface to allow a Transaction Program (TP) to request a
conversation to another TP through an LU 6.2 - LU 6.2 session.

In analogy to TCP/IP, the LU 6.2 - LU 6.2 session could be compared with a
three-way TCP/IP handshake, and the TP could be compared with the application
that is using the TCP/IP session. A DSU can act as multiple TPs just like any
application can handle multiple incoming TCP/IP ports, or have multiple outgoing
TCP/IP sessions. A DSU can be analogous to an SMTP mail server.

The TP uses APPC commands to interface with the LU 6.2 to request a conversation,
send data, and end a conversation with a partner TP on another LU 6.2.

For example, a TP would use the ALLOCATE command to request the LU 6.2 to
initiate a conversation with a named partner TP at a named partner LU 6.2.

SNADS uses specific TP names to represent the functions of sending and receiving
SNADS distributions (mail).

  TP name for sending SNADS FS1 distributions: X'21'001
  TP name for receiving SNADS FS1 distributions: X'21'002

The notation above for the TP names indicates that the TP name begins with the
(non-printable) character with hexadecimal code 21, and ends with the printable
characters 001 or 002.

The SNADS connector emulates a DSU in that it implements the X'21'001 and
X'21'002 Transaction Programs.

The SNADS connector will use the TP_STARTED, ALLOCATE, SEND_DATA, CONFIRM,
DEALLOCATE, and TP_ENDED commands during the process of starting up, sending a
message to the Host (or AS/400) system, and shutting down.

The SNADS connector will use the RECEIVE_ALLOCATE, RECEIVE_AND_WAIT, CONFIRMED,
TP_ENDED commands during the process of starting up, receiving a message from
the Host (or AS/400) system, and shutting down.

Additional query words:

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Keywords          :  
Technology        : kbExchangeSearch kbExchange550 kbZNotKeyword2
Version           : winnt:5.5
Issue type        : kbinfo

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