Asynchronous Serial Communications Programmer's Reference Manual (32022-90052)

132 Chapter7
Programming for PAD, DTC Telnet, Telnet/iX Server, and VT Devices
PAD Access to MPE/iX Systems
PAD Access to MPE/iX Systems
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.