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Configuring and Managing Host-Based X.25 Links: HP 3000 MPE/iX Computer Systems > Chapter 1 Introduction
X.25 Network Connections |
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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.
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. 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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![[X.25 Network Connections]](img/gfx1.gif)