Linux at the BBC - page 2
DHCP and DNS
The BBC uses Linux to provide almost all the internal DNS and DHCP services. In fact, if a few stopped, there would be serious trouble. I believe we have about 30,000 machines dependent on Linux-run DHCP/BOOTP for IP addressing and maybe even a few more dependent on Linux-run DNS for address resolution. We use BMC's Software Patrol to monitor the Linux operating system and have written bespoke modules to monitor DNS/DHCP.
Digital Text Service
Ceefax, I should explain to readers outside the UK, is a system which encodes services in plain text for viewing alongside TV. However, rather than being addressed to a particular recipient and sent over the Internet, it is broadcast along with the TV signals from the BBC and other UK broadcasters in the UK and some European countries. Suitably equipped TVs can decode it and get access to several hundreds of pages of text, typically from the BBC's news service (news/tv-listings/weather). It is quite an old system; the graphics capabilities are limited to a text-only screen, roughly 40x25 charactors in size. The newer Digital text server should be faster with more interactivity and features, such as hyperlinks, real TV-quality image stills, proportional anti-aliased fonts and quarter-screen actual TV image while browsing.
The channel and signals for this service, known as an MHEG stream, are melded into the end broadcast stream before actual transmission by expensive dedicated hardware. With the MPEG video data which provides the TV pictures, the digital text services are transmitted into millions of homes in the UK.
The stream of digital text data that is pumped in to this hardware in TV Centre in London is transmitted over TCP/IP on a lowly 10base2 (thinnet) cable from Linux. It is a dual-redundancy system with a complete double-up of every element.
The Linux boxes are low-cost PCs running a slim Slackware setup, with nothing apart from basic network utils and a single ELF binary called 'spam' (Spoolfile Playout And Management system) that takes parameters and talks over TCP/IP to the dedicated hardware. The main idea is that, if one dies, we can cheaply and quickly get a replacement box installed and running. We can, of course, immediately switch to the fail-over system, as there is full redundancy--but would only be running on one leg until we got the replacement in place. So far the biggest problem has been network cards failing or losing IRQ/IO settings.
If the daemons on both Linux PCs stopped or both boxes went down, it would immediately halt the digital text service. In the Ceefax (Teletext) world this is equivalent to the text completely freezing, the clock not ticking on, the numbers not cycling through any more, etc... This is very serious.
Their daemons take a file called a "spoolfile carousel", which they constantly cycle through, playing out the contents. This file is updated via FTP from an E250 UltraSPARC Sun running Solaris2.6. A number of tcl scripts and C binaries which accept data from various sources in the BBC, mainly (at the moment) from Ceefax/News, convert this into the compiled MHEG spoolfiles before uploading. Our data is always up-to-date, with the latest weather/news/tv schedules, and it is this right-on-time delivery that puts the BBC, as a corporation, ahead of the opposition.
So in this case it is easy to see how the Linux machines are pivotal to the Corporation's core business of providing news...in a highly visible position, too.
Rapidly needed webservers
In a few instances a PC has been quickly converted into a Linux webserver for the development or demoing of a website,where a local drive wouldn't work--for example where SSI (Server Side Includes) or CGIs were used. BBC Online used to do most of the development on a few basic Linux PCs, though we're moving them to Solaris so that the development environment matches what we use on the Internet. The BBC TV show 'Tomorrow's World', which I should explain for non-UK readers is a well-established TV programme about new technology and scientific advances, hosted the Turing Test where three studio guests were shown using a web interface one-to-one chat system. They had to chat for 5 minutes and determine if they were talking to a computer or a human.
The same system had run for a week before the show on the BBC Web site. There was one human and 2 computer programs; the programs were from outside sources, and I wrote the CGI wrapper interface for the public to chat to them or the human. For the show, which went out live, we had a Linux box with apache and the same setup as the BBC servers for the CGI interface. It performed flawlessly on the night, as you'd expect. I'd tried to get Linux on the desktop machines, which would help show that Tomorrows World was a cutting-edge show, but there were complications and not enough time, so in the end it had to be Windows clients.
We also use Linux for lots of other little things almost too trival to mention. For instance:
the webcam we have looking towards the Millennium dome;
http://news.bbc.co.uk/hi/english/static/domecam/default.htm also has a Linux box below it running the realencoding software recently released by www.real.com;
the award-winning Osprey cam site from http://www.bbc.co.uk/animalzone/, sadly now no longer in use, used a 4-year-old Linux box and gfx capture card. The linux box would dial up to a local ISP to save money, then ftp the images at regular intervals up to the webserver. A phone line was put in especially for this, as it is in an incredibly remote moor in Scotland--about 3 hours drive from any large city! This ran fine for months and allowed us to diagnose and fix any faults with ease, as we could connect in and have the same control as if it were right next to us.
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