Steps for diagnosing logon problems

Several steps must take place successfully to establish an X.25 virtual circuit for TCP/IP activity:

An X.25 call request is received by the X.25 NPSI server from the X.25 network (incoming call) or is sent by the X.25 NPSI server to establish a connection to a new destination (outgoing call).
An X.25 call accept confirms the X.25 call request. Call accept is sent by TCPIPX25 for an incoming call, or received from the X.25 network for an outgoing call.
NPSI initiates an SNA session with the X.25 NPSI server application by using a VTAM® LOGON.

Each of these steps is reported in the activity log, shown in the X.25 trace examples. Problems fall into two main areas: failure of the X.25 call itself, indicated by either a refusal or an immediate clear, or failure of the NPSI LOGON. Call failures are reported with X.25 cause and diagnostic codes. Standardized cause codes include:

Code: Meaning
00: DTE clearing. The remote system cleared the call.
01: Number busy. The called number cannot accept another call.
03: Invalid facility request. A facility that is requested by the caller is not subscribed or conflicts with a subscribed option.
05: Network congestion. Congestion conditions or some other problem within the network temporarily prevent the requested virtual circuit from being established.
09: Out of order. The called number is out of order.
0B: Access barred. The caller is not permitted to obtain a connection to the called number.
0D: Not obtainable. The called number is not assigned or is no longer assigned.
11: Remote procedure error. An X.25 protocol error at the remote equipment.
13: Local procedure error. An X.25 protocol error.

See X.25 NPSI Diagnosis, Customization, and Tuning for a list of diagnostic codes. X.25 networks can also have special diagnostic codes in the range 80–FF.

VC LOGON can fail for various reasons. Among the most common reasons are:

Incorrect VTAM switched circuit definitions. IDNUM entries are error prone; SSCPFM=USSNTO and DISCNT=(YES,F) are necessary.
A default VTAM USS table ISTINCDT that is modified to include text in the message 10 entry.
Coding LOGAPPL on the NPSI X25.VC definitions. Use LOGAPPL only on the X25.MCH and on the X25.VC with the Fast Connect feature.
Insufficient number of type 1 LUs configured on the NCP LUDRPOOL statement.

A VTAM buffer trace with ID=VTAM helps diagnose the first problem. Collect the following configuration documentation before you contact the IBM® Software Support Center. X.25 NPSI server configuration data set, VTAM APPL definition for the NPSI X.25 server, NPSI definitions, and VTAM SWNET definitions for NPSI.