HP OpenVMS Systems

• X.25 Server/Client (X.25 over DECnet)
• LLC2 (X.25 over LAN)
• XOT (X.25 over TCP/IP)

The above methods require an external machine to act as a gateway or relay to the X.25 connection or PSDN. The X.25 for OpenVMS Integrity server provides the interface for the actual synchronous line and may be implemented using an OpenVMS Alpha system with a PBXDP or PBXDD synchronous communication controller, or a third party dedicated router.

Note:X.25 native communication using synchronous communication controllers on OpenVMS Integrity servers will not be supported.

In this configuration, Systems A, B and C could communicate with System D. System C could be implemented as an Alpha system with a synchronous communication controller PBXDP or PBXDD, or as a third party router that supports X.25 Server (X.25 over DECnet) and synchronous communications.

Advantages of this configuration are that since DECnet is a routable protocol, the systems may be interconnected over wide area network. In addition, the actual networking backbone could be provided by TCP/IP and then use DECnet-over-TCP/IP for the X.25 client/server connection. One disadvantage for this configuration is that DECnet and X.25 Server/Client are implemented with proprietary protocols.

• Pure LLC2
• LLC2 used in conjunction with a relay system which allows X.25 traffic to be "relayed" from the LLC2 link to some other linkage such as a sync card.

Both configurations are outlined in the following diagram:

In the configuration shown, System A can communicate with System B using X.25 over LLC2. Both System A and B could also communicate with System C, and if System C was configured with X.25 Relay, Systems A and B would also be able to communicate with System D.

System C could be implemented as an Alpha system with a synchronous communication controller PBXDP or PBXDD, or as a third party router that supports LLC2 and synchronous communications.

The Relay system can be configured with different types of connections such as the synchronous line shown, or by running X.25 over TCP/IP. Many different types of third party router hardware exists that can provide the functionality of System C. LLC2 is not a routable protocol and so is limited to use on a LAN or Extended LAN.

In this configuration System A can communicate via X.25 with System B; either A or B can communicate with System C which in turn could be configured with X.25 Relay allowing A & B to communicate with system D.

System C could be implemented as an Alpha system with a synchronous communication controller PBXDP or PBXDD, or as a third party router that supports X.25 over TCP/IP and synchronous communications.

Advantages of this configuration are that since TCP/IP is a routable protocol, the systems may be interconnected over wide area network. As with LLC2, there are many vendors that provide XOT functionality in dedicated routers. The connectivity between System C and System D could be via a synchronous line/PSDN; a point to point connection (leased line) or even an ISDN connection (using a dedicated device to connect from the sync line to an ISDN interface.

In this configuration the Windows XP Pro system would establish a PPTP connection to the Windows 2003 Server (or even another XP Pro system). Once the VPN connection was established (and assuming that the Windows systems were configured for internet connection sharing), the two X.25 systems running XOT could communicate.

The major advantage of this configuration is that it completely eliminates the need for a synchronous communication adapter. This configuration is also secure, since the PPTP connection can have 128 bit encryption. The existing X.25 legacy application to continue functioning with no noticeable change (from the application perspective) to the network environment.