Many of the communications services available for HP 3000
Series 900 systems are provided through the Datacommunications and
Terminal Controller (DTC). There are six types of DTCs currently
supported: DTC 72MX, DTC 48, DTC 16, DTC 16iX, DTC 16MX and the
DTC 16RX. The DTC 72MX, DTC 48 and the DTC 16 can support the DTC/X.25
Network Access cards that make communications over X.25
networks possible. The DTC 16iX, DTC 16MX and the DTC 16RX
do not support the DTC/X.25 Network Access cards.
The DTC 72MX allows up to three connector
cards, plus a LAN card. Up to three DTC/X.25 Network Access cards
are supported. The DTC 48 can contain up
to six connector cards, up to three of which may be DTC/X.25 Network
Access cards. Slot 0 must contain an asynchronous connector card,
but slots 1 through 5 can contain any combination of asynchronous
cards and DTC/X.25 Network Access cards. The DTC 16
can contain up to two asynchronous connector cards and, optionally,
a DTC/X.25 Network Access card as its third card.
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 | NOTE: Throughout this manual, all DTCs supporting X.25 connections
will be referred to generically, unless their type is significant
to the topic under discussion. |
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X.25 System-to-System Connections |
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Host-based X.25 system-to-system connections are supported
through the DTC/X.25 iX Network Link. This
NS 3000/iX link makes it possible for you to connect a
HP 3000 Series 900 system to a public or private X.25 packet switched
network (PSN).
The DTC/X.25 iX Network Link requires that you have at least
one DTC/X.25 Network Access card installed in a DTC. You must also
purchase and install the X.25 iX System Access
software on the system.
Device Connections Via PAD |
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PAD support makes it possible for asynchronous serial devices,
such as terminals and serial printers, to be connected to the system
through an X.25 network. Serial devices are connected to a PAD,
or Packet Assembler/Disassembler.
A PAD converts asynchronous
character streams into packets that can be transmitted over a packet
switched network. PAD packets follow the CCITT X.25 protocol recommendations.
The PAD support provided on MPE/iX systems conforms to the
1984 version of CCITT recommendations X.3 and X.29. Support is also
provided for the 1980 recommendation. Packet sizes of 128, 256,
and 512 bytes are supported. Access is provided for users of asynchronous
serial 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 several cluster
controllers for use as private PADs.
All devices connected via PAD must support XON/XOFF protocol
and must be configured to match the speed of the PAD and modem.
Only character mode and VPLUS applications are supported on
PAD-connected devices. There are also some aspects of the way transmission
occurs over PAD connections that cause differences in the way certain
device control operations take place. See the Asynchronous
Serial Communications Programmer's Reference Manual
for a summary of these differences.
Figure 1-1 “X.25 Network Connections” shows both PAD
and X.25 system-to-system connections for HP 3000 Series 900 systems
employing host-based network management.
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