An NCP line trace, CSS line trace, or NTRI line trace records activity on a designated line attached to the communication controller. If you run a line trace on an inactive line attached to the communication controller, the line trace does not collect any data.

The NCP line trace information in this topic is NCP version and release sensitive.

NCP V5R3 and later

NCP has a transmit and receive correlator in the status entries of the line trace data to show the order in which the transmits and receives occurred. ACF/TAP sorts the trace records by the correlator and formats them on the line trace summary report in the order of occurrence. NCP does not unblock blocked PIUs in the line trace data.

NCP V6R1 and later

You can use the NCP line trace to trace the interface between NCP and an Ethernet-type subsystem (ESS) adapter or to trace frame-relay lines on a TSS or high-performance transmission subsystem (HPTSS) adapter.

The amount of data to be traced for frame-relay lines on HPTSS adapters is limited to a maximum of 58 bytes (before V7R5).

Except for CSS lines, NCP collects all duplex trace data in two different chains of buffers before sending the trace data to the host. One chain contains a trace of activity over the transmit leg of duplex lines; the other chain traces the activity on the receive leg. When the host receives a record trace data (RECTRD) request/response unit (RU), the data is either all from a transmit leg or all from a receive leg.

Restriction: Only one NTRI line trace (physical or logical) can be active at a time.

NCP V6R2 and later

Use the CSS line trace to trace the interface between NCP and resources attached to the 3746 Model 900.

NCP does not support the NCP line trace for communication lines driven by user-written line control code, unless the user's adapter control blocks (UACBs) are compatible with the NCP's adapter control blocks (ACB). The request to start or stop the line trace is passed to the user-written I/O code. At that point, the user-written code must support the trace. NCP handles line trace requests for user-written line control if it is compatible and if you code COMPACB=YES on the GROUP definition statement. For more information about the UACB, see the NCP and SSP Customization Guide, LY43-0031 and NCP and SSP Customization Reference, LY43-0032.

For the NCP line trace, HPTSS, Ethernet-type LAN, and CSS lines are to be considered high-speed lines.

NCP V6R3 and later

Synchronous data link control (SDLC) lines attached to the 3746 Model 900 with SPEED=1000000 or greater on the LINE definition statement are also considered as high speed.

Restrictions: (before V7R5)

• Only one high speed line can be traced at one time.
• The amount of data to be traced for high speed SDLC lines is limited to a maximum of 40 bytes.

NCP V7R5 and later

When you start a line trace you have the option to specify the number of bytes of data to trace. Starting with V7R5, the number of bytes of data that NCP can trace has been expanded. Table 1 lists the maximum number of bytes that NCP traces for a specific line type.

Starting with V7R5, you can activate more than one line trace even when a line trace is active for a high-speed line. The number of line traces that can be active at one time is limited by the LTRACE keyword on the BUILD statement, which has a maximum value of eight. For restrictions on NTRI line traces, see NTRI line trace and NTRI IOH trace.

NCP V7R7 and later

You can activate a line trace for frame-relay logical lines on a transmission subsystem (TSS) or HPTSS adapter. Table 1 shows byte trace limitation values.

Table 1. Byte trace limitations

Line type	Maximum number of bytes
NTRI physical	200
NTRI logical	Unlimited
SDLC (TSS or HPTSS)	Unlimited
FR physical (TSS or HPTSS)	200
FR logical (TSS or HPTSS)	Unlimited
ESS	Unlimited
CSS	Unlimited