X.25 Handler Configuration

Introduction

This document describes the individual commands used in the configuration file for the X.25 handler on the FarSync intelligent X.25 cards. An overview of the file format and description of the configuration process is contained in the main X.25 Handler Configuration document.

Some example configurations are also available for comparison with the command descriptions.

X.25 Configuration

The commands here are divided into logical sections although ordering within the file is rarely important.

Throughout this document commands shown are in UPPER CASE, however lower case or even mixed case commands are permitted and equivalent.

Most of the system parameters have default values that will be used if no appropriate command is found in the setup file.

Advanced Commands

Many command configure advanced features or parameters that rarely need changing from the defaults. These commands can normally be ignored and omitted unless you have a specific need.

Advanced commands are highlighted in pink to indicate that they can normally be skipped.

File Commands

QUIT

Commands are read and processed in succession until the QUIT command is reached. Any text after this line is ignored.

Basic Line Definition Commands

Commands in this section define parameters relevant to the physical configuration of an individual X.25 line.

LINE NUMBER=

Each FarSync card has more than one X.25 line, and each line requires separate definitions. This command defines the line number to be used by any line specific commands that may follow it. Note that line numbers must be defined in ascending order starting with 0. There is no default for for this command – it must be entered explicitly.

The X.25 software supports V.24/RS232, V.35 and X.21 (V.11) interfaces. Valid protocol parameters for this command are: V24 (the default), V35 and X21.

This command may alter the default card channel (see below), and should therefore be entered before before the BOARD CHANNEL command.

The SPEED parameter defines the speed of the line and is used for performance optimisation, and when clocks are generated internally. The speed may be defined in terms of bits per second (bps) or kbps. For example:

LINE BAUD RATE= 19200 or LINE BAUD RATE= 19.2k
LINE BAUD RATE= 64000 or LINE BAUD RATE= 64k

BOARD CHANNEL=

The default depends on the line protocol being used – channel A for X.21 and V.35 and channel B for V.24.

The X.25 Handler requires that the RS232 Modem signals DCD & CTS be active for the line to be up. In order to be resilient to noise on these lines, a debouncing algorithm is implemented. When a change of state occurs, the signal must remain stable for the period defined by the TIME parameter for the change to be accepted. If further changes occur, the signal is assumed to be in the initial state until a period of stability is detected, when the final state is used to determine whether the line is up. If the signal remains unstable for a period greater than the LIMIT parameter, then the line is assumed to be down.

Both parameters are defined in clock TICs (20 tics per sec, or 1 tic = 50mS). The defaults are TIME=3, LIMIT=92.

DTR LOW

If this option is included, DTR will be held low by the X.25 Handler for leased line operation (i.e. not dialup).

ENABLE RESTART DELAY

If the X.25 line goes down, the X.25 Handler will attempt to restart it after a short delay to allow the modem signals to stabilise. If this command is used, the delay will be extended to 15 seconds.

GENERATE CLOCKS

This command will cause the card to use its own internal clock for operation at the speed defined by the LINE BAUD RATE command. An additional crossover cable will be required to use this option.

By default, clock generation is disabled.

IGNORE MODEM SIGNALS

If this option is selected, the X.25 Handler will ignore the state of the CTS and DCD signals for RS232 or the I (Indication) signal for X.24, and assume that the line is connected at the physical level.

TIMERS LINE STARTUP= <value in seconds>

The LINE STARTUP timer specifies the time the X.25 Handler waits for the line to become active at Level 1. (It is assumed active when both CTS and DCD are high, and flags are received). When this timer expires, the line is restarted by dropping RTS & DTR and then raising them again. The default value is 10 seconds; it is suggested that it should be set higher (e.g. 100s) if using manual dialup operation.

X.25 Link Configuration Commands

Commands in this section define parameters relevant to the operation of an individual X.25 link, and must follow the LINE NUMBER command. The commands are divided into 3 sub-sections: parameters describing the operation of the link at more than one level, parameters relevant to the level 2 only, and parameters relevant to level 3 only.

X.25 Link Configuration – General

CCITT COMPLIANCE

This command prevents the use of non-CCITT compliant options; it should only be required if the software is being certified to NET2 standards or similar. This command will also prevent the use of extended diagnostic codes.

EXTENDED FUNCTIONS

This command enables the use of some extended functions, shown below, in the 1984 recommendation of X.25:-

Non-zero DTE clearing cause codes in the range of 128 to 255.
32 byte interrupt packets.
Transmission of Diagnostic packets (DCE Operation only).

It will also cause Packets on unassigned channels to be cleared instead of being ignored, unless CCITT COMPLIANCE is selected.

EXTENDED SEQUENCES

This command will cause the X.25 Handler to select Modulo 128 operation for both level 2 and level 3. The default is modulo 8 operation.

HOMOLOGATION

This command is useful if the software is to undergo homologation (i.e. certification testing) for e.g. NET2. It performs the same actions as the following commands:-

CCITT COMPLIANCE
DISABLE CLEAR ON RESET
DISABLE CONSTANT POLLING
DISABLE EXTRA DIAGNOSTICS
DISABLE RESTART ON STARTUP
PERMIT UNKNOWN CALLERS

LOGICAL DCE

If this command is included, the software will assume logical DCE operation, at both level 2 and level 3. Default is logical DTE operation. (Note that a Logical DTE must be connected to a Logical DCE at the other end of the X.25 link for communication to take place, so this command is required at one end if using two X.25 cards in a back to back configuration.)

X.25 Link Configuration – Level 2

DISABLE CONSTANT POLLING

The X.25 Handler normally polls the other station (transmits RR command frames) periodically if the line is idle. This command prevents it from doing so.

ENABLE SELECTIVE REJECTS

The X.25 Handler can make use of the HDLC Selective Reject (SREJ) frame at level 2, if this command is included.

Note that Selective Rejects are not part of X.25 or LAPB, so this command may only be used in special circumstances, e.g. connecting two X.25 cards back-to-back, without using an X.25 network.

It is recommended that this command be used in conjunction with extended level 2 sequence numbers.

EXTENDED FRMRS

The X.25 Handler can use some non-CCITT extensions of the FRMR diagnostic code (byte 3 of the information field) if this command is included.

EXTENDED LEVEL2 SEQUENCES

This command will cause the X.25 Handler to select Modulo 128 operation for level 2 only. The default is modulo 8.

LEVEL2 OPERATION <param>

Some networks require different operation at level 2, particularly for approval testing. This command selects different link level operation options. Valid parameters are:

DATEX-P
TYMNET
PASSIVE

The PASSIVE option may be combined with other options; it allows the software to respond to DCE initiated or DCE solicited startup. This command should normally be omitted.

The X.25 Link Level timers T1 and T3 can be set using this command. T3 is set indirectly by giving a value to the Maximum Repeat Count N2 (T3 = T1 x N2). The default values used by the software in the absence of this command are: T1 = 2 seconds (dependent on line speed) and N2 = 10 seconds.

The default value for T1 is dependent on the line speed (default 9600 bps); for faster lines T1 can be reduced, and should be increased for slower lines. T1 may be defined in terms of tics (20 tics per second, or 1 tic = 50mS) by specifying the TICS1 parameter.

WINDOW LEVEL2= <level 2 window size>

This command defines the level 2 window size variable k. This may be from 1 to 7 if using modulo 8 operation, and from 1 to 127 if using modulo 128 operation (extended sequence numbers). The default is 7.

X.25 Link Configuration – Level 3

where <chan> is from 1 to 4095 (in decimal).

These commands allows the user to define which logical channel numbers to use for incoming, outgoing or bothway virtual calls. These are normally determined by the network.

The CHANNEL is a combination of the Logical Channel Group Number together with the Logical Channel Number within the group: CHAN = (LCGN * 256) + LCN. E.g.:

Note that a network logical channel number can only be assigned once. The logical channel numbers given in this command must correspond with those allocated by the network.

Up to 254 LCNs per line may be defined.

This command must be entered explicitly – there is no default.

Example (typical PSS line with 10 Bothway channels):-

CHANNELS BOTHWAY= 1024 TO 1033

It is possible to specify only one LCN to be used, e.g.

CHANNELS BOTHWAY= 1024 ONLY

CHANNELS PVC= <low chan> TO <high chan> [PACKET= <packet size> WINDOW= <window size > ] [PASSIVE | IMMEDIATE]

where <chan> is from 1 to 4095 (in decimal). This command allows the user to define a range of Permanent Virtual Circuits. Optionally, the packet and window sizes may be defined if these are to be different to the Normal sizes for the link. In addition, the default connect action can also be defined using the PASSIVE or IMMEDIATE keywords; if neither is defined, the connect action will be ACTIVE.PVCs may be configured in addition to (or instead of) SVCs, but it is recommended that SVCs should be used wherever possible, assuming that both are available. PVCs may be configured in a number of ranges, each range having its own configuration parameters associated with them. The packet and window size for each PVC must be configured correctly (i.e. the same as the sizes at the other end of the PVC), otherwise problems will result. By default, they are the same as the normal (default) packet & window sizes for the link.

There are 3 different actions that may be taken when connecting to a PVC. The default Connect Action for the PVC is configurable, and may be overridden by the application at connect time. The actions are:

The different types of actions are defined for master/slave or peer-to-peer scenarios. In a back-to-back configuration, then either one side should be Active and the other Passive, or both Immediate.

DISABLE EXTRA DIAGNOSTICS

The X.25 Handler uses some non-CCITT diagnostics codes when clearing or resetting calls due to errors. These may be disabled by the use of this command.

DISABLE NEGOTIATION

This command disables the use of window and packet size negotiation. The sizes used will be determined by the value of the NORMAL parameters in the WINDOWS and PACKET commands below.

DISABLE RESTART ON STARTUP

This command prevents the X.25 Handler from issuing a Restart Request Packet when it starts up the line (DTE operation only; if LOGICAL DCE is selected, a Restart is always issued on line startup).

EXTENDED LEVEL3 SEQUENCES

This command will cause the X.25 Handler to select Modulo 128 operation for level 3 only. The default is modulo 8.

NEGOTIATE DOWNWARDS

Some networks always negotiate packet sizes downwards instead of towards 128 as defined by CCITT. Using this command allows the X.25 Handler to use downwards negotiation of packet sizes.

This command defines the packet size that will normally be used in calls and the maximum packet size that can be utilised. The frame level uses the maximum packet size to determine the maximum frame size (parameter N1). If the maximum is greater than the normal packet size then the X.25 handler will attempt to negotiate up to the maximum when possible. The normal packet size may range from 16 to 4096 bytes (in powers of 2) and the maximum from 128 to 4096 bytes.

The defaults if no packet size command is included are:-

Normal 128
Maximum 128

The Normal parameter MUST be the same as the network default packet size, otherwise problems may occur during data transfer giving rise to packet level resets or link level Frame Rejects (FRMR Y). The default value should work on most networks.

Note that the Maximum packet size parameter determines the size of internal buffers. Care should be taken when using a large packet size if a large quantity of logical channels and/or a large window size is also required, as there may be insufficient memory.

The X.25 Packet Level timers T20, T21, T22, T23 can be set using this command. The default values used by the software in the absence of this command are :-

T20 20
T21 200
T22 180
T23 180

T20 is the timeout for Restart Requests, T21 for Call Requests, T22 for Reset Requests and T23 for Clear Requests.

Window sizes may take any integral value from 1 to 7 (modulo 8) or from 1 to 127 (modulo 128). The normal and maximum window size parameters are used if window size negotiation is required. If the maximum window is greater than the normal window then the X.25 software will attempt to negotiate up to the maximum when possible. If no WINDOWS command is included, the defaults are :-

Normal 2
Maximum 2

The Normal parameter MUST be the same as the network default window size, otherwise problems may occur during data transfer giving rise to packet level resets. The default value should work on most networks.

Auto-Dial and X.32 Configuration Commands

This section describes the commands used to configure V.25 bis auto-dial and X.32 operation, and should be ignored if auto-dial is not to be used. Commands are relevant to a single line definition only except where stated in the text.

AUTO DIAL BACK

This command declares that Auto Dial Back is to be used. This command is only meaningful in conjunction with the DIALUP command. Note that it will also be necessary to define an XID send string.Auto Dial Back operates as follows :- the X.25 Handler makes the dialup connection, and exchanges identification strings. Once the XID exchange is complete, it disconnects the dialup connection, and waits for the other end to call it back. Once the incoming telephone call has been received, the X.25 Handler starts up level 2 without any further XID exchange.

Note that an auto-answer modem is required for auto dial back operation.

DIALUP

This command configures a line for V.25 bis auto-dial operation. Note that any of the commands below that start with DIALUP will activate this command as well.

DIALUP CONNECT TIMEOUT= <time in seconds>

This command defines the timeout period on establishing a dialup connection. The default is 90 seconds.

DIALUP DTR HIGH

If this command is used, DTR will be held high by the X.25 Handler. This allows incoming telephone calls to be accepted, but is incompatible with DUAL MODE operation.

DIALUP DUAL MODE

If this command is included, then it is assumed that there are 2 lines connected to the modem, a leased line for normal use (selected by holding DTR low), and a dialup line for backup use if the leased line fails (selected by raising DTR).

DIALUP NUMBER= <telephone number>

This command defines the default telephone number to be used for auto-dialing, if none is specified explicitly by an application. The number string may contain V.25 bis command characters as well as the telephone number digits (i.e. ‘<‘, ‘>’, ‘=’, ‘:’, and ‘;’).

DIALUP IDLE PERIOD= <time in seconds>

This command defines the period that a dialup line may be idle (i.e. the time after the last X.25 call on the line is cleared) before the dialup connection is dropped. The default is 60 seconds.

NUI='<NUI string>’

If this command is included, then the NUI facility will be included in each Call Request made by the X.25 Handler. The NUI string is defined within single quotation marks (‘), any Hex characters being prefixed by the # character and being terminated by non-hex characters, allowing the string to be defined as a mixture of Hex and ASCII. The NUI string may be up to 64 bytes in length.

This command should not be used if LOGICAL DCE operation is selected.

XID

This command declares that XID frames are to be used when the link starts up, if dialup operation has been selected. The contents of the XID frames, if any, are defined by the XID SEND and XID RECEIVE commands below.

Note that any of the commands below that start with XID will activate the command as well.

XID ALWAYS

This command declares that XID frames are used at link startup for leased line as well as dialup operation.

XID RECEIVE='<XID Receive string>’

This command defines the contents of the XID Information field, if any, that must be present in received XID frames. This allows the X.25 Handler to verify that the other link station is entitled to establish a link level connection.

The XID string is defined within single quotation marks (‘), any Hex strings being prefixed by the # character and being terminated by non-hex characters, allowing the string to be defined as a mixture of Hex and ASCII. The XID string may be up to 64 bytes in length.

XID SEND='<XID Send string>’

This command defines the contents of the XID Information field in transmitted XID frames.

The XID string is defined within single quotation marks (‘), any Hex strings being prefixed by the # character and being terminated by non-hex characters, allowing the string to be defined as a mixture of Hex and ASCII. The XID string may be up to 64 bytes in length.

XID send strings are normally required for auto-dial back, and when the network or remote DTE requires to verify that the X.25 Handler is entitled to make the connection.

Name, NUA and Security Configuration Commands

This section describes the commands that may be used for configuring names. Names are used by the X.25 Handler to refer to NUAs (Network User Addresses), and may also be used to refer to TSAPs.

Note that commands in this section are relevant to the operation of the X.25 Handler as a whole (i.e. apply to all lines).

ALLOW REVERSE CHARGING

Incoming calls that request reverse charging are normally not accepted by the X.25 Handler. If, however, this command is included in the setup file, the incoming call will be accepted.

DISABLE CALL NUA

This command prevents the caller’s NUA (and subaddress if specified) from being included in CALL REQUEST packets. Removal of the caller’s NUA is required on some X.25 networks.

DISABLE CASE SENSITIVITY

Names used by the X.25 Handler are normally case sensitive. If this command is used, the case of alphabetic characters in Names is ignored.

INSERT MAIN ADDRESS

This command causes the LINE ADDRESS or MAIN ADDRESS (if configured) to be inserted before the calling NUA in CALL REQUEST packets, provided that there is space to do so.

Note: the LINE ADDRESS (if defined) is used in preference to the MAIN ADDRESS.

LINE ADDRESS= <nua>

This command defines the main portion of the Network User Address without the subaddress. This allows incoming calls that just contain the called subaddress to be accepted. An example of a network where this command would be useful is TRANSPAC in France.

Note: unlike MAIN ADDRESS, this command is specific to the current line definition.

Local names are used by application programs to identify themselves to the X.25 Handler. Normally applications will define their own names, but if using the X.25 Handler as a NetBIOS emulator, then Local names with their corresponding NUAs must be defined in the setup file by using this command.

The local name command allows a Name/NUA pair to be defined for local use; all such local names operate in STDMODE, unless the TRANSPORT parameter is included, in which case the name operates in TNBMODE. The NUA may be any length from 1 to 15 digits, and so may include a subaddress. NUAs must be unique if they are to be used for incoming calls, except Transport NUAs (the NUA parameter must be preceded by the TRANSPORT parameter), and transport and non-transport names may not share the same NUA.

The optional SOCKET number defines the last byte of the name in decimal format; this overrides the last character defined in the Name string. Note that if defining two or more names that are the same except that some have a socket numbers and one does not, the name without the socket number must be defined last.

The number of Local names that may be defined is dependent on the size of the name table; this may be modified by using the MAXIMUM NAMES command.

MAIN ADDRESS= <nua>

This command defines the main portion of the Network User Address without the subaddress. This allows incoming calls that just contain the called subaddress to be accepted. An example of a network where this command would be useful is TRANSPAC in France.

Note: unlike LINE ADDRESS, this command is not line-specific.

The size of the name tables is configurable, in order to make the best use of the available memory. There are 4 name tables, containing Local names, Remote Names, TSAP-ids and XNAD-ids. The latter two are only required if using the Transport module. Note that Local names are considered to be a subset of Remote names.

This command may be used to extend or reduce the name table sizes. The default and maximum allowed are as follows :-

PERMIT UNKNOWN CALLERS

The X.25 Handler contains an access security feature whereby the Calling NUA of an Incoming Call is checked against a list of NUAs (the names in the Remote Name table) to make sure that only calls from known originating NUAs are accepted. Note that for this purpose, Local Names are considered to be a subset of Remote Names.

This security feature can be disabled by including this command in the setup file.

Note that when this command is included, a remote name will be assigned to unknown calling NUAs; this name will be the calling NUA, prefixed by the character ‘N’, and space filled. The name may be added to the remote name table in some circumstances, depending on the nature of the program using the X.25 Handler interface, in which case the call will be cleared if the remote name table is full.

PREVENT REVERSE CHARGING

This command is the opposite of the ALLOW REVERSE CHARGING command.

PREVENT UNKNOWN CALLERS

This command is the opposite of the PERMIT UNKNOWN CALLERS command.

The REMOTE NAME command allows a remote destination to be ‘named’ together with its NUA. The NUA may be any length from 1 to 15 digits, and so may or may not include a subaddress.

Remote names may be used by users of the PAD interface or by other applications when specifying the destination when making a call. They may also be used to define calling NUAs to be allowed to connect, if using the Access Security feature (see PERMIT UNKNOWN CALLERS). The number of Remote Names that may be defined is dependent on the MAXIMUM NAMES command.

The optional socket number defines the last byte of the name in decimal format; this overrides the last character defined in the Name string. Note that if defining a name with a socket number that is otherwise the same as one without, the name with the socket number must be defined first.

If the OUTGOING parameter is included, the name may only be used for outgoing calls.

Note: Incoming calls from remote names not defined are added automatically if the PERMIT UNKNOWN CALLERS command is specified. These are given a name based on the calling NUA, prefixed by N; e.g. a call from NUA 234273400156 will cause the name N234273400156 to be added automatically.

If PERMIT UNKNOWN CALLERS is not included in the setup file, the remote name and NUA of any callers must be defined using this command, and the OUTGOING parameter must not be used. Any other callers will be refused access.

See the X.25 Handler Programmers Guide and Technical Reference Manual for more information on remote names.

REMOVE CALLING MAIN ADDRESS

When making call requests, the main address is subtracted from the calling NUA, leaving just the subaddress, if this command is included.

REMOVE CALLING NUA ENTIRELY

This command is the same as DISABLE CALL NUA, removing the calling NUA when call requests packets are sent.

Miscellaneous Configuration Commands

This section contains commands relevant to the general operation of the X.25 Handler.

Note that commands in this section are relevant to the operation of the X.25 Handler as a whole (i.e. apply to all lines).

DISABLE CLEAR ON RESET

This command allows calls to continue should a level 3 reset occur on the channel.

Note that application programs may control this parameter explicitly themselves.

DISABLE IMPLICIT

This command prevents dialup connections from being established without an explicit dialup request. Refer to the X.25 Handler Programmers Guide and Technical Reference Manual for details of explicit and implicit auto-dial requests. This command is not specific to an individual line, but is relevant to all.

DISABLE STATISTICS

This command will disable the gathering of statistics. This has the effect of saving card CPU cycles, improving performance.

ENABLE APPLICATION DIAGNOSTICS

This command enables the use of application specified cause and diagnostic codes when clearing X.25 calls. Note that the X.25 Handler may change the non-zero cause codes, depending on whether the line being used is configured for 1984 functionality.

MAXIMUM CONNECTIONS= <number of user sessions>

This command defines the upper limit on the number of concurrent user sessions supported by the X.25 Handler. The number of sessions are calculated based on the number of X.25 channels, and the configuration of the SNA, DSP and Transport modules, and then the upper limit is applied. The default for this command is 254 .

Line Monitor Configuration Commands

The FarSync cards contain a facility to capture and buffer data for user display via a controlling application (fsx25mon). The combination forms an effective line monitor.

Enables the monitor and sets the initial level of monitoring. QUIET indicates that the monitor is available although no data is being gathered. FRAME collects frame level data and likewise PACKET packet level information. DATA collects the packet level data only and CONTROL the calls and clears only. The default is for monitoring to be disabled. If QUIET is selected, the fsx25mon application will set a new level when started.

MONITOR BLOCKS= <number of blocks to reserve>

Defines the number of blocks to reserve for monitoring in a circular buffer; each block is 1kbyte in size. The monitoring application must drain the buffer before this limit is exceeded or the monitor will lose data. (On the other hand, allocating too much memory for the monitor will reduce the amount available for the buffers needed by the X.25 software.)

MONITOR CELL SIZE= <size of data capture>

Defines the amount of data to capture for each event. It is not normally necessary or efficient to capture all the data, but better just to capture the headers and some initial data.

Transport Configuration Commands

This section contains transport configuration options. None of these commands is required in order to use ISO Transport; they just alter the default configuration options.

The CLASS and ALTERNATIVE parameters define the default preferred and alternative classes respectively. Valid classes are 0, 1, 2 and 3. If the ALTERNATIVE parameter is to be included it must be preceded by the CLASS parameter. The defaults are class=3, alternative=2.

The NO FLOW CONTROL parameter defines that non-use of explicit flow control is to be selected with Class 2 connections.

Note that applications will normally select these parameters explicitly in their connection requests, so they will not normally be required.

TRANSPORT IPA3

If the IPA3 parameter is included, then each X.25 Call Request made by the transport module will have 4 bytes of call user data: C4000000 in hex. Transport T-CONNECT user data will not be sent. This parameter should be included if calls to ICL hosts are to be made and the application is not able to specify the network call user data itself. Note that not all ICL Hosts require Call User Data.

TRANSPORT MAX CIRCUITS= <number of circuits per X.25 lcn>

The MAX CIRCUITS parameter defines the maximum number of transport connections per X.25 channel. The default is 5.

TRANSPORT QUALIFIED

This command enables the use of qualified data transfer; this is a non-ISO extension to transport, and should only normally be required when using certain other FarSite programs.

The TTR timer defines the time, in seconds, to reassign an outgoing transport connection to a network connection for Class 1 and Class 3 connections. The TWR timer defines the time to wait for for the reassignment of an incoming transport connection. The default for the TTR timer is 30 seconds and the default for the TWR timer is 120 seconds.

The TS1 timer defines the timeout period on responses to CR TPDUs, and the TS2 timer defines the timeout period on responses to DR TPDUs. The defaults for both timers are 60 seconds.

The NETWORK IDLE PERIOD timer is the time a multiplexed network connection may be idle (i.e. have no transport connections assigned to it) before being cleared. The default time is 50 seconds.

TRANSPORT TPDU SIZE= <size in bytes>

The TPDU SIZE parameter defines the default preferred maximum TPDU size. Valid values are 128, 256, 512, 1024, 2048, 4096 and 8192. If none is specified, the default is calculated based on the X.25 packet and window size.

TRANSPORT USER DATA ROUTING

This command should be used if transport names are to share the same NUA as an X.25 name. It causes the X.25 Handler to examine the call user data in incoming X.25 calls, to determine whether the call should be routed to the transport entity. If the call user data is 4 or more bytes long, starting 03010100 in hex, then the call is assumed to be for the transport entity.

TRANSPORT USER DATA ABSENT

This command should be used in conjunction with the TRANSPORT USER DATA ROUTING command above to route incoming X.25 calls with zero length call user data to the transport entity. It also causes the X.25 Handler to omit the default call user data when making X.25 call requests for use by transport connections.

TRANSPORT ZERO DIAGS

If this command is used, then X.25 virtual circuits used for transport connections will be cleared with cause 0, diagnostic 0, otherwise non-zero diagnostics will be used instead.

PAD Configuration Commands

This section describes the commands that may be used to configure the Triple-X PAD module in the X.25 Handler.

PAD PROFILE DEFAULT= <n:v, n:v, ….>

This command allows the user to alter the default PAD profile. The parameters are defined as parameter number followed by parameter value; the comma separator characters are optional, as long as there are spaces between the PAD parameter values. Illegal values are ignored.

The FarSync PAD parameters are specified as parameters T1, T2, T3 and T4. E.g.

PAD PROFILE DEFAULT=3:2, 10:0, 19:1, T4:1

PAD PROFILE ID= <profile id> PAR= <n:v, n:v, ….>

This command allows the user to define alternative PAD parameter profiles. The profile ID is a string of up to 8 characters. When the profile is defined, the parameter values are pre-set to those of the default profile, so the user need only defined those parameters that are different to the default profile.

If this command does not fit on a single line in the setup file, then remaining parameter values may be defined on the next line by repeating the command but with the remaining parameter settings. E.g.

PAD PROFILE ID=prof1 PAR=1:1, 2:0, 3:2, 4:0, 5:0, 6:1
PAD PROFILE ID=prof1 PAR=10:0, 13:0, 15:0

This command allows the user to customise the PAD prompts. The prompts are 20 bytes strings defined within single quotes. Control and special character sequences may be defined in hexadecimal by preceding the hex sequence by the hash # character, a non hex character terminating the hex sequence (NB this character is not treated as part of the string).

The PAD FREE PROMPT is displayed when no call is in progress; the PAD ENGAGED PROMPT is displayed when a call is in progress and the user has escaped to PAD command level, and the PAD DATA PROMPT is displayed when the PAD changes from command level to data transfer level.

The defaults are :-

FREE ‘> ‘
ENGAGED ‘* ‘
DATA ”

PAD WELCOME MESSAGE= <multi-line 500 character string>

This command allows the user to customise the welcome message displayed when a user connects to the PAD. The string may be up to 500 characters and occupy several lines in the setup file. The first character is treated as the message delimiter; all characters until the next delimiter character are included in the welcome message.

The default welcome message is
“<CR><LF>Welcome to the PAD Service<CR><LF>”

where <CR> is the carriage return character (0x0D) and <LF> is the line feed character (0x0A)

IGNORE NATIONAL OPTIONS

If this command is included then any X.29 parameters in a SET or SET AND READ command following the national options marker are ignored, otherwise an error indication message is transmitted.