Technical data

Figure 2–1 Trace Records
Protocol header information
from protocol layers
Network protocol data
User data
Trace record data:
event code
size
time
tracepoint name
context data
2.1.1 Local and Remote Tracepoints
There are two types of tracepoint:
• Local tracepoints are those found within host-based VMS networking products
such as VAX P.S.I.
• Remote tracepoints are those found within server-based networking products
such as the DEC WANrouter 100/500.
Using CTF from a VMS system, you can trace:
• All local tracepoints
• All remote tracepoints on servers for which the VMS system is a load host
For security reasons, you cannot trace tracepoints on remote VMS systems.
2.2 How CTF Collects and Displays Trace Records
When networking software generates a trace record, it calls CTF to signal that a
trace record is available for collection.
If you have instructed CTF to collect trace records from this tracepoint, CTF
collects the trace record; otherwise, CTF ignores the trace record, which is
therefore lost.
Collecting a trace record involves:
1. Copying the trace record from the network software that generated it into an
internal CTF buffer.
2. Making the contents of the trace record available to the user. Since the trace
record is produced in machine-readable form, it must be analyzed (that is,
formatted into user-readable form) before it can be printed or displayed.
There are three ways in which CTF collects trace records and makes them
available to the user: detached tracing, live tracing, and snapshot tracing.
2–2 Technical Overview