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System control

LIVE-NET is controlled by a computer which provides a booking system for the sessions and controls the video crosspoint switches and other equipment. Since the system had to have multi user access and be able to provide low level access to external devices it was decided to use a computer which ran the UNIX operating system.

In 1991 the original computer (a BT 68020 box) was damaged by a mains transient and proved to be impossible to repair. Since the system was UNIX based and written mainly in C it was possible to get the LIVE-NET programs up and running on the new computer (a SUN IPC) in under two days. Most of this time was spent tracing a bug in one of the programs which relied on a peculiarity of the hardware architecture of the 68020.

The original version of the LIVE-NET software was written by two postgraduate computer science students between 1987 and March 1989. Nine months later in November 1989 another programmer was employed to work on maintaining, debugging and enhancing the system.

Instead of using a single large monolithic program to control LIVE-NET, the system was split into three separate smaller programs each of which control their own part of the system [see figure 4]. The programs communicate with each other by passing messages between themselves. switch controls the video crosspoint switches and keeps track of the current configuration of the system. dbp looks after the bookings database and is responsible for scheduling sessions. When a session is due to start or finish dbp communicates with switch telling it what crosspoints to set on the video switches. livenet is a screen based interface to the other two programs which is used to insert or modify sessions or manually make network connections.

Rather than develop a new control system SuperJANET uses a modified version of the LIVE-NET interface, booking and switching programs.

The paradigm used when designing the LIVE-NET software was of a simply connected star network with video switches connected to the control computer either directly or via the fifth data channel. To the computer this would appear as a direct connection.

In early 1990 the data links were disconnected from the computer and used to provide the Livenet Data Network (LDN). This was the first network to provide IP connectivity within London University and acted as the basis for the Janet Internet Protocol Service (JIPS).

To provide control of the remote switches a Packet Assembler Dissembler (PAD) connected to the JANET X-25 network was wired to the serial lines of the control computer. Each of the remote video switches was connected locally to a PAD. Changes had to be made to the control program to make it call the remote PAD and set up a connection between the LIVE-NET computer and the remote switch.

LIVE-NET 2 is not connected to JANET and has to control CODECS, Ascends and the LVR as well as the video switches. Further modifications were made to the control program to allow it to access the network interface of the computer. This allows equipment connected to the Internet to be controlled. Equipment can either be connected to another computer (with a small control program running on that machine) or a terminal server.

Since the Internet is a global network there is no reason why LIVE-NET can not control equipment beyond the bounds of Greater London. Today London, tomorrow the world !!

Apart from the section of code which opens a connection to the equipment whether directly from a serial port, via an X-25 PAD or an Internet connection the changes were transparent to the rest of the program

As well as the three main control programs several other programs were written for use with LIVE-NET. These included programs to control the Laser Video Disc Recorder (LVR), report generation programs to produce statistics of system usage and list the sessions for given dates and programs to provide low level control of other parts of the LIVE-NET control system.

The main report generation program produces a schedule of the sessions for a given time period (Appendix B). This program translates the location names given in the booking form to a more useful form. The printed output is sent to the site representatives as a record of the sessions for their site and also serves as a central reference. In practice it is far quicker to look up a session in a printed listing than to retrieve it from the computer.

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