Introduction

The following sections describe parameters related to the ACC Mux Subsystem that may be modified to reflect system requirements. All of these kernel tunable parameters can be modified by inserting them into /stand/system file (in all lower case) and specifying a new value for them.

In addition, many of these parameters may be modified after the system has booted using the n2z_cntrl utility program. This utility is used to modify the current setting of the parameter. Note that the parameter value takes effect (is used) for an X.25 link when x25init is executed to configure (or reconfigure) that link. Modifying a tunable with this utility will not change the setting of the parameter on X.25 links that have already been configured (exceptions will be noted). Those parameters that can be modified with this utility are noted below.




	NOTE: Hewlett-Packard does not support any customer modifications to the files described in the following sections beyond what is described here unless specific support arrangements have been made.

n2z_max_zlu

The n2z_max_zlu parameter defines the maximum number that may be used for a Level 2 ZLU or Level 3 ZLU through the interfaces provided by the X.25/9000 product. Note that each X.25 link and each Virtual Circuit uses one ZLU. The PORTTEST and MONITOR ZLU definitions must also fall in this range.

The default n2z_max_zlu value is 16384 which should be adequate for almost all configurations. This value should be greater than or equal to the Terminal-ZLU parameter in the TTGEN configuration file. (Refer to Chapter 4 “ZCOM Mux Subsystem Configuration” for more information on the TTGEN file parameters.)

The n2z_max_zlu value is used to allocate table space internal to the ACC Mux Subsystem software. This means that increasing or reducing this value affects the amount of memory required to run the ACC Mux Subsystem. Each entry in the table takes 4-bytes, so with the default value the table size is 64K bytes.

If n2z_max_zlu is modified, the system must be re-built using mk_kernel, and rebooted for the change to take effect.

In the case of Z7300A, the 4-Channel ACC multiplexer interface, the n2z_max_zlu parameter should allow for expanded Terminal-ZLU parameter values, based on the maximum number of subchannels that will be used through the X.25/ACC subsystem.

n2z_max_cards

This parameter defines the maximum number of MUX cards that will ever be defined in a ttgen configuration file. The MUX number specified in an ACC X.25 device file must be less than this value. n2z_max_cards has a default value of 32. This value can be overridden by specifying a new value in /stand/system.

For example, if the largest expected ttgen configuration on a given system will define muxes 0 through 12, the n2z_max_cards parameter must be set to at least 13.

If n2z_max_cards is modified, the system must be re-built using mk_kernel, and rebooted for the change to take effect.

n2z_log_rst_clrs

This parameter controls whether every X.25 VC Clear Request/Indication and Reset Request/Indication should have information logged in the nettl logging file. If this parameter is set to one, messages are logged containing the X.25 Cause and Diagnostic codes present in the Clear/Request packet, the ZCOM level 2 and 3 ZLUs of the link and VC on which the Clear/Reset occurred, and the calling and called address information used in the original call request to setup the SVC. N2z_log_rst_clrs has a default value of 0. That is, no additional information is logged about VC Resets and Clears.

Note that you may also dynamically turn clear/reset logging on and off using the utility n2z_cntrl. To turn logging on use the following command“n2z_cntrl -l1”. To turn logging off use the command “n2z_cntrl -l0”. Modifying this parameter with n2z_cntrl immediately takes affect on all X.25 links.

n2z_max_ninb_pkts

The n2z_max_ninb_pkts parameter specifies how many inbound data packets should be buffered for a virtual circuit before instructing the ACC Mux card firmware to hold off further inbound data packets for that virtual circuit. Increasing this value will increase the amount of system memory that will be allocated to handle the inbound data packets.

N2z_max_ninb_pkts has a default value of 6 which is adequate for most situations.

If n2z_max_ninb_pkts is modified, the system must be re-built using mk_kernel, and rebooted for the change to take effect.

n2z_low_bnd_npkts

The n2z_low_bnd_npkts parameter specifies the point at which the ACC Mux Subsystem should instruct the ACC Mux card firmware to begin sending up inbound data packets again for a virtual circuit. This value should always be less than the value of n2z_max_ninb_pkts.

N2z_low_bound_npkts has a default value of 3 which is adequate for most situations.

If n2z_low_bnd_npkts is modified, the system must be re-built using mk_kernel, and rebooted for the change to take effect.

n2z_ignore_cts_cd

This parameter defines the ACC behavior for the Carrier Detect (CD) and Clear To Send (CTS) modem lines. By default, when CD or CTS drops, the X.25 link is brought down by the ACC. This may not be desirable in some cases because certain brands of modems do not provide stable CD and CTS signals. You may set this parameter to one to cause the ACC to ignore the state of the CD and CTS modem lines. This means that an X.25 link failure will only be detected through the Level 2 protocol which could take well over 3 minutes.

n2z_ignore_cts_cd has a default value of 0. That is, CTS and CD are monitored and will bring the X.25 link down. Note that the program n2z_cntrl can be used after the system is up to change the value of this parameter for a specific X.25 line. The procedure to change this parameter for a specific link(s) is to first run n2z_cntrl to change the parameter value, then run x25init on each X.25 link that requires this behavior. Finally, re-run n2z_cntrl to set the parameter back to its default value to prevent other X.25 links from using this setting. If you run this program with no parameters, it will display a usage string.

If n2z_ignore_cts_cd is modified in /stand/system, the system must be re-built using mk_kernel, and rebooted for the change to take effect.

n2z_end_to_end_acks

This parameter defines the ACC behavior for D-bit acknowledgments. By default, D-bit acknowledgments are handled automatically by the firmware. When a request is made to transmit a data message with the D-bit set, the driver will acknowledge the D-bit request immediately after the data message has been acknowledge by the level 2 protocol. When a data message arrives with the D-bit set, the X.25 firmware does not wait for the application to read the data before sending the D-bit acknowledgment (RR).

N2z_end_to_end_acks has a default value of 0. That is, application end-to-end acknowledgments for D-bit data packets are disabled. Setting this parameter to one (1) enables end-to-end acknowledgments. In this case, D-bit message handling behaves as documented in the X.25/9000 Programmer's Guide. Note that the program n2z_cntrl can be used after the system is up to change the value of this parameter for a specific X.25 line. The procedure to change this parameter for a specific link(s) is to first run n2z_cntrl to change the parameter value, then run x25init on each X.25 link that requires this behavior. Finally, re-run n2z_cntrl to set the parameter back to its default value to prevent other X.25 links from using this setting. If you run this program with no parameters, it will display a usage string.

If n2z_end_to_end_acks is modified in /stand/system, the system must be re-built using mk_kernel, and rebooted for the change to take effect.

n2z_t25_disable

This is used to enable or disable the use of the X.25 T25 timer. This parameter controls whether the X.25 firmware will time out unacknowledged level 3 data packets. If the value is 0, this timer is enabled. If the value is 1, the timer is disabled. The default is “enabled”.

N2z_t25_disable has a default value of “enabled”. Note that the program n2z_cntrl can be used after a system is up to change the value of this parameter for a specific X.25 line. The procedure to change this parameter for a specific link(s) is to first run n2z_cntrl to change the parameter value, then run x25init on each X.25 link that requires this behavior. Finally, re-run n2z_cntrl to set the parameter back to its default value to prevent other X.25 links from using this setting. If you run this program with no parameters, it will display a usage string.

If n2z_t25_disable is modified in /stand/system, the system must be re-built using mk_kernel, and rebooted for the change to take effect.

n2z_hold_acks

This is used to enable or disable the use of the Hold Acknowledgments option. When this parameter is set to 1, all level-3 acknowledgments (RRs) for received packets are suppressed until the receive window is full. In addition, the level-3 acknowledgments are also suppressed when the T2 timer expires. When this parameter is "disabled" (0), level-3 RRs are handled normally.

N2z_hold_acks has a default value of "disabled" (0). Note that the program n2z_cntrl can be used after a system is up to change the value of this parameter for a specific X.25 line. The procedure to change this parameter for a specific link(s) is to first run n2z_cntrl to change the parameter value, then run x25init on each X.25 link that requires this behavior. Finally, re-run n2z_cntrl to set the parameter back to its default value to prevent other X.25 links from using this setting. If you run this program with no parameters, it will display a usage string.

If n2z_hold_acks is modified in /stand/system, the system must be re-built using mk_kernel, and rebooted for the change to take effect.

n2z_rr_policy

The n2z_rr_policy parameter is used to select the method that will be used to acknowledge (level 3 RR packet) inbound data packets. If this parameter is set to zero, the ACC Mux card will send a level 3 RR (acknowledgment) for every data packet received. If n2z_rr_policy is set to one, then the MUX firmware adopts a policy that attempts to minimize the number level 3 RRs sent.

N2z_rr_policy has a default value of 0. Note that the program n2z_cntrl can be used after a system is up to change the value of this parameter for a specific X.25 line. The procedure to change this parameter for a specific link(s) is to first run n2z_cntrl to change the parameter value, then run x25init on each X.25 link that requires this behavior. Finally, re-run n2z_cntrl to set the parameter back to its default value to prevent other X.25 links from using this setting. If you run this program with no parameters, it will display a usage string.

If n2z_rr_policy is modified in /stand/system, the system must be re-built using mk_kernel, and rebooted for the change to take effect.

n2z_link_timeout

The n2z_link_timeout parameter specifies the length of time in seconds that the ACC Mux Subsystem will wait for the X.25 line to shutdown before exiting with an error. Note that the shutdown process continues in the background when a timeout occurs.

N2z_link_timeout has a default value of 90 seconds which is adequate for most situations.

If n2z_link_timeout is modified, the system must be re-built using mk_kernel, and rebooted for the change to take effect.

zcom_mem_size

The ACC Mux Subsystem reserves a contiguous block of kernel memory for tables for its use. This block of memory is used for table space and for buffering internal to the ACC Mux Subsystem product.

The maximum size of the memory block is set by the value of parameter zcom_mem_size. This is specified in the system file used to build your kernel. The default value (4 MBytes) should be adequate for most configurations. The zcom_mem_size value can be sized to reflect what is actually required for a given system configuration.

In the case that zcom_mem_size is not set to a large enough value for the given X.25 configuration, the program ZMON will not be able to be scheduled. It will report that it does not have enough memory to start up. If zcom_mem_size is large enough to hold the internal tables, but is not large enough to handle the buffering between the ACC Mux card and the ACC Mux Subsystem drivers, the subsystem will still function, but the performance will be degraded.

If zcom_mem_size is not large enough, it is suggested that the X.25 configuration be reviewed to make sure that all of the configured X.25 Level 2 connections, and all of the configured virtual circuits are expected to be used. If possible, the configuration should be reduced to reflect what is actually required. (Note that the configuration file that determines the necessary zcom_mem_size value is the /opt/acc/cfg/x25.answ file. This file is directly affected by what is given in the x25init configuration file.)

zcom_mem_size should never be set less than the “Total Size” value which is reported when TTGEN is run with the -s option. The algorithm below can be used to estimate a reasonable value for zcom_mem_size.

If zcom_mem_size is modified, the system must be re-built using mk_kernel, and rebooted for the change to take effect.

zcom_mem_size = <card> * <rate> * <time> * (<length> + 200) * 1.5

where:

<card>: number of mux cards on the system
<rate>: maximum number of messages per second per mux card calculated as follows:

<rate> = (<bps_rate> * <num_ports> * <duplex>) / <msg_len>