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PAD Access to MPE/iX Systems
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If you have X.25 cards, the programs you write may be used to control devices connected through a packet switched network (PSN) to a PAD device.

A PAD, or Packet Assembler/Disassembler, is a device that converts asynchronous character streams into packets that can be transmitted over a packet switching network. PAD packets follow the CCITT X.25 protocol recommendations.

This part includes discussions of the following:

  • The physical components of a network with PAD support.

  • Limits and restrictions that apply to PAD-connected devices.

  • Security for PAD access.

  • Considerations when using terminal control intrinsics with PAD devices.

PAD Access to MPE/iX Systems

The PAD support provided on MPE/iX systems conforms to the 1984 version of CCITT recommendations X.3 and X.29. Packet sizes of 128, 256, and 512 are supported. Access is provided for users of asynchronous devices connected to both public and private PADs.

A public PAD is a service provided by a Public Data Network (PDN), such as TELENET or TRANSPAC. Public PADs can be used with either a dial-up or a leased line.

A private PAD is one that is connected to a PDN as a host node having its own X.25 network address, but behaves as a PAD when connected to another node. Private PADs require leased lines to the network. Hewlett-Packard provides the HP2334A, HP2334A Plus, and HP2335A cluster controllers for use as private PADs.

Hardware Requirements

PAD access is provided to MPE/iX networks through a DTC/X.25 Network Access card mounted in the DTC. Three types of DTCs support X.25 connections—the DTC 16, DTC 48, and DTC 72MX. In the DTC 48 and DTC 72MX, each access card takes the place of a terminal connect card in one of the DTC slots, and each DTC may contain up to three network access cards. DTC 48s may not have the access card in slot 0. See the DTC Planning Guide for more information on the DTC hardware. In the DTC 16, there are three slots. The first two slots can contain direct connect or modem cards, and the third slot can contain only a network access card.

The DTC is connected to the LAN as usual, with the MPE/iX systems to which it has access also connected to the LAN.

Figure 7-1 "DTC/X.25 Network Access for PAD" depicts PAD access to HP 3000 Series 900 Systems via a DTC equipped with the DTC/X.25 Network Access card.

Figure 7-1 DTC/X.25 Network Access for PAD

[DTC/X.25 Network Access for PAD]

Network Configuration Requirements

The parameters for asynchronous devices that can use the PAD support facility provided by the DTC are configured through either the OpenView DTC Manager or through host-based configuration. PAD support information for each MPE/iX host system must be supplied via NMMGR configuration.

PAD Configuration Values

Most of the characteristics that define how asynchronous devices connected through a packet switched network will act are determined by the configuration of the PAD itself. See the documentation for the PAD for more information on how to define the characteristics of its devices.

PAD support for the network is configured, in part, through the OpenView DTC Manager or through host-based configuration. Configuration values are entered to define the types of devices that may access the network. Levels 1 through 3 of X.25 must also be configured.

PAD support parameters for each MPE/iX host system that will allow device connections via PAD must be defined in the NMMGR configuration, along with the device profiles to be associated with PAD devices. PAD devices requiring non-logon (programmatic) access must be configured as nailed PAD devices. Devices that require only logon access can be configured as non-nailed PAD terminals.

Security

Several levels of security are provided to assure that no unauthorized access can be obtained to the MPE/iX systems on your network.

See Using the OpenView DTC Manager for more information on configuring and using security for incoming PAD calls.

For host-based security information, see Configuring and Managing Host-Based X.25 Links.

PAD Device Access

All devices supported for asynchronous connection to the DTC can be connected via PAD. The devices must support the PAD and modem port configuration.

Hewlett-Packard provides a special terminal type file, terminal type 24, for support of terminals connected via PAD. PAD support is provided for serial printers with printer types 18 or 26.

Log On Access

If a terminal is properly configured for the PAD it is connected to, and PAD connections are allowed for the MPE/iX network you are accessing, you can establish a terminal session on a desired MPE/iX system.

You must first establish a connection from the PAD to the system you want to open the session on. You may choose to access a specific MPE/iX system directly by entering that system's X.25 address in the connection request. Alternatively, you may access the DTC Switching User Interface by entering the X.25 address of the DTC and connect to the system you want by using the connection request provided by the DTC Switching User Interface. (Regardless of how you choose to initiate your connection, you will be able to switch between host systems on the LAN once you terminate your session.)

NOTE: When connected via PAD, you must log-off with the MPE :BYE command to return to the PAD prompt. It is not possible to escape from data transfer with a session active.

Your virtual connection is not disconnected until you log out from the DTC switching user interface or until the inactivity timer configured via the OpenView DTC Manager expires.

Only character mode and VPLUS block mode applications may be run from PAD devices; no other types of block mode may be used.

Programmatic Access

Terminals and serial printers can be accessed programmatically if they are connected to a private PAD and configured as nailed devices on the MPE/iX host on which the application is running. To open a device programmatically you use the FOPEN or HPFOPEN intrinsic with the device option specifying the ldev number or device class that was associated with the remote device through the NMMGR configuration.

General PAD Restrictions

Some basic limitations apply to the way transmission occurs and to the operations that are supported over PAD connections:

  • It is necessary to press [Return] to forward data from the PAD across the network to the DTC even if the byte count specified in the read is reached.

  • Some special character sequences, such as subsystem break ([CTRL]Y by default), must also be forwarded with a [Return].

  • You cannot use a PAD terminal as a console.

  • Use of customized terminal and printer types files is not supported over PAD.

  • You cannot use the :STARTSESS command with ldevs that allow PAD device connections.

  • Typeahead mode is not supported over PAD on versions prior to release 4.5, C.45.00.

  • Binary mode transfers are not supported between a PAD terminal and a MPE/iX or HP-UX host on versions prior to release 4.5, C.45.00.

  • User Block Mode and HP Block Mode applications are not supported on PAD devices.

  • Parity generation and checking is not supported programmatically over PAD.

  • The line deletion response ([CTRL]X echo characters, !!! by default) cannot be enabled or disabled programmatically over PAD (though some PADs allow you to define line deletion characters locally).

  • PAD printers cannot be shared by more than one host.

PAD Programming Considerations

Most file system intrinsics can be used to control devices connected to PADs as if the devices were locally connected. Both the FCONTROL and FDEVICECONTROL intrinsics are supported for PAD device control. In most cases the device control calls work as normal.

There are, however, a number of differences in the way device control functions operate over PAD connections. The individual differences in the operation of each FCONTROL and FDEVICECONTROL call are documented in the Intrinsics Reference chapter of this manual. The following summary is provided here for your convenience.

FCONTROL

Some FCONTROLs are ignored by PAD. These are calls that attempt to control some function that is not supported over PAD, such as changing terminal speed or setting parity. These calls will return a CCE condition code, but no device control action will take place. Any values returned in these calls may not be a true reflection of device control settings. These FCONTROLs include:

  • FCONTROL(10), set line speed.

  • FCONTROL(11), set line speed

  • FCONTROL(23), disable parity checking.

  • FCONTROL(24), enable parity checking.

  • FCONTROL(34), allow printing of [CTRL]X echo.

  • FCONTROL(35), disable printing of [CTRL]X echo.

  • FCONTROL(36), define parity setting.

  • FCONTROL(40), determine current speed.

Reads following a call to FCONTROL(27), which enables binary mode, return a CCL condition code with the file system error FSERR20 (INVALID OPERATION), until binary mode is disabled (FCONTROL(26) ), if you are using a version prior to release 4.5.

Calls to FCONTROL(37), to set both terminal type and speed, will change the terminal type setting, but will have no impact on how the device actually operates. A CCE condition code will be returned. (Note that this is a difference from how PAD devices behave on MPE V systems.)

Some caution should be taken when using FCONTROL(4), which sets a timeout interval for a read. Keep in mind that some delays may be caused by the network over which the PAD is transmitting. In such cases you may want to add some time to the timeout value you would normally specify for the call.

FDEVICECONTROL

The FDEVICECONTROL intrinsic is also supported on MPE/iX systems with PAD connections. However, there are also several limitations on the device control operations they perform. The following FDEVICECONTROL parm1 values, with 192 specified as the controlcode, will return a CCE condition code but have no effect on the operation of the device or the transmission of data:

parm1

Action

1

Specify terminal type or printer type file

3

Set line speed

9, 11

Enable/disable parity checking

10, 12

Set parity type

14

Set line deletion response

26

Enable/disable XON/XOFF flow control

27

Set XOFF timer value

29

Define block mode alert character

30

Define block mode trigger character

51

Set typeahead mode

55

Select backspace response action

56

Specify data bits per character

60

Flush typeahead buffer

61

Bypass typeahead buffer

62

Set quiesce I/O

63

Set single echo typeahead mode

64

Ignore parity error on input mode

65

Set inter-byte timer

66

Define multiple type 2 EOR characters (AEOR)

67

Delete (DEL) to backspace (BS) mapping

68

Enable/disable escape sequence read termination

69

Enable/disable suppress echo of read termination characters

73

Set FCLOSE timeout value

FDEVICECONTROL also verifies that a terminal is configured as a PAD device. A parm1 value of 28 (controlcode 192) returns a value corresponding to the type of block mode supported by the driver. A value of 15 is returned by this call when the device is a PAD terminal supporting (VPLUS) page block mode.



Chapter 7 Programming for PAD, DTC Telnet, Telnet/iX Server, and VT Devices

DTC Telnet Access to MPE/iX Systems