X25AM Configuration and Management Manual

PTrace for the X25AM Subsystem
X25AM Configuration and Management Manual—523424-004
6-14
What to Look for in Level 3
What to Look for in Level 3
The following example PTrace command allows you to view only the level-3 packets:
? SELECT L3; FILTER NOSM; FILTER NOINTERNALS
After level 2 is synchronized, you should see one restart packet sent and confirmed in
the trace, with level 3 synchronized. The level 3 appearance differs depending on
whether it is a permanent virtual circuit (PVC) or a switched virtual circuit (SVC).
If your side is a PVC, you may see data packets sent whenever the file-system call
warrants it (that is, WRITE = 1 data packet out) and RR received after WINDOW SIZE
is reached at the remote.
If your side is an SVC, data cannot be sent until the logical circuit is established. You
should see the SVC sending call request packets, with the correct called (destination)
and calling (source) addresses included. There might also be some user data and
facility fields appended at the end of the call request packet. The remote side checks
the called DTE address field of the call request packet it receives, verifies it against its
own configured subdevice addresses, and then responds with either a call accept
packet (if OK) or a clear packet (if not). The clear packet should contain a clear
diagnostic byte explaining why the call was cleared. However, for network-generated
clear packets are often specific to the PDN. Consult the PDN specification for
clarification.
Most X25AM problems are caused by wrongly cleared calls. These problems can
usually be traced to incorrectly configured subdevices or lines being set for an incorrect
NETADDR. Check the subdevices’ NETADDR and PORT values to be sure that the
values match. In some cases calls are cleared because the network was configured
with an incorrect NETID. The NETIDs (DATANET, DATAPAC, DATEXP, DDN, DDXP,
PSS, TELENET, TRANSPAC, TWINET, TYMNET, X25, X25NP, X25SA, X25UD, and
X25XA) specify different methods of addressing that support a variety of PDNs. See
Appendix D, Using the NETID Modifier.
In some cases, calls are cleared because the DCE cannot accept the call negotiation
values in the facility fields.
Another item to note is the usual default value for the line attribute EXTENDED. If
EXTENDED is off, then level 3 automatically clears any incoming packets with
extended user data in call, clear, or interrupt packets. The default value for
EXTENDED is off, which causes problems with some PDNs that require the extra data.
Receive Ready* RRR0 0001
Receive Not Ready* RRR0 0101
Reject* RRR0 1001
Table 6-4. Packet Types (page 2 of 2)
* RRR = N(R) acknowledges all data packets received -1. SSS = N(S), number of data packets sent. M = More
bit (more data follows).