APPC Subsystem on MPE/XL Node Manager's Guide (30294-90007)

Chapter 1 23

Introduction

The APPC Subsystem

The LUs on an HP 3000 node can be conﬁgured as dependent LUs or

independent LUs.

•Adependent LU can communicate only with dependent LUs on a

Type 5 (host) node. It functions as a secondary LU; that is, it cannot

issue a BIND to initiate an APPC session. When a dependent LU

wants an APPC session with the host, it must wait for the host to

send the BIND. It can send an INIT_SELF request to the host,

requesting that the host send a BIND, or it can be conﬁgured to

accept unsolicited BINDs. A dependent LU can carry on only one

session at a time.

•Anindependent LU can communicate directly with an

independent LU on a Type 2.1 (peer) node, like an IBM AS/400. The

APPC subsystem allows the HP 3000 to operate as a Type 2.1 node

in a peer-to-peer environment, where two Type 2.1 nodes can

establish APPC sessions between themselves without the

supervision of the SSCP on a host node.

An independent LU can function as either a primary or a secondary

LU; that is, it can initiate a session by sending a BIND to the remote

LU, or it can receive a BIND from the remote LU.

An independent LU on the HP 3000 can carry on multiple (parallel)

sessions with a remote independent LU. It can also carry on sessions

with several remote independent LUs at once; however, all the

remote LUs with which it communicates must be connected to the

HP 3000 through the same local SNA node (the same copy of

SNA/SDLC Link/XL).

Some remote systems, like the IBM AS/400, can perform

intermediate routing between nodes in an SNA network. An

independent LU connected to one of these systems can take

advantage of its routing capabilities to communicate with nodes that

are not directly connected to the HP 3000.

Figure 1-3 shows an HP 3000 directly connected to two IBM AS/400s

and to an IBM host. A separate copy of SNA/SDLC Link/XL is required

for each HP-to-IBM connection.

The dotted lines in Figure 1-3 represent APPC sessions.

Independent LU INDLUA on the HP 3000 is conducting a session with

independent LU AS400LU1 on IBM AS/400 #1. INDLUA cannot

communicate with either of the remote independent LUs AS400LU2 or

AS400LU3, because they are connected to the HP 3000 through a

different local SNA node (a different copy of SNA/SDLC Link/XL).

Independent LU INDLUB on the HP 3000 is conducting three parallel

sessions with independent LU AS400LU2 on IBM AS/400 #2. INDLUB is

also conducting a session with AS400LU3 on IBM AS/400 #3. INDLUB can