HP 3000 Manuals

Configuring and Managing Host-Based X.25 Links

X.25 Network Connections 

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 16MXand the DTC 16RX. The DTC 72MX,
DTC 48 and the DTC 16 can support the DTC/X.25 Network Access cardsthat
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 72MXallows up to three connector cards, plus a LAN card.  Up to
three DTC/X.25 Network Access cards are supported.  The DTC 48can 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 16can contain up to two
asynchronous connector cards and, optionally, a DTC/X.25 Network Access
card as its third card.


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.


X.25 System-to-System Connections 

Host-based X.25 system-to-system connections are supported through the
DTC/ X.25 iX Network Link.  This NS3000/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 Accesssoftware on the system.

Device Connections Via PAD 

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 protocolrecommendations.

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 PADis a service provided by a Public Data Network (PDN), such as
TELENETor TRANSPAC. Public PADs can be used with either a dial-up or a
leased line.

A private PADis 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 controllersfor 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 (32022-61001) for a summary of these
differences.

Figure 1-1  shows both PAD and X.25 system-to-system connections for
HP 3000 Series 900 systems employing host-based network management.


          Figure 1-1.  X.25 Network Connections 

MPE/iX 5.0 Documentation