XFOR: Understanding How SNADS Connector Uses LU 6.2

ID: Q215473

The information in this article applies to:

Microsoft Exchange Server, version 5.5

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:

Keywords :
Version : winnt:5.5
Platform : winnt
Issue type : kbinfo