BBC Wales problems

i remember several years ago when the feed from pebble mill went dead as bbc two midlands opted out for the midlands at westminster, sutton coldfield re-broadcast bbc two south's the south on sunday, which suggests RBS still works during opt outs.

i guess things may have changed, or with there being sports rights involved, a mechanism might be in place to protect for bbc two north?

5:25 - "Now on BBC 1 Wales, we join Diane-Louise Jordan; this really is, 'Songs of Praise'."

At least he realised his mistake. Still Network on Analogue, though... (and still is, as of 6:00)

EDIT: BBC 1 Wales appears to back on Analogue (according to Ceefax) as of 6:15 - just in time for the Welsh news!

RBS (Rebroadcast Standby) is a pretty simple but effective system to maintain transmission in the event of a transmitter losing its main feed. If this happens, the transmitter switches to rebraodcasting the signal it receives from the next nearest transmitter. In the scenario tvmercia mentions above, Sutton Coldfield rebroadcast the signal received from Beckley (Oxford, BBC South). If a regional opt occurs when another transmitter in in RBS mode, then the opt is carried on both transmitters. It's quite an elderly system but it works. I doubt when it was put in, sports rights were such an issue. Certainly I don't know of a system that prevents RBS from kicking in during certain opts, though there may be something in place in the North for the Superleague Show. I would have thought that some sort of 'force majeur' agreement would cover the 'accidental' transmission of SLS to a neighbouring region.

RBS is tested once in a while (often in January) and is usually accompanied by much activity on this forum as the Testcard makes it's appearance across the country. During this test, they pull the plugs out of the network feeds, leaving Crystal Palace as the only transmitter with a direct feed. All transmitters are forced to go into RBS mode and so the quality of the testcard can be seen to be deteriorating the further away you get. It's worth pointing out that RBS is an analogue only system. Presumably as regions are switched off, more and more holes will appear in the chain and so eventually it will become effectively obsolete.

surely there must be some sort of backup in place for digital?

The digital transmitters are fed in a much more complex manner - and the backups are different.

AIUI analogue transmitters only had a single network feed (some may have had additional oddball stuff when they were midpoints for others) - so the second feed for backup WAS usually RBS. This was because transmitters were fed by both microwave, cable and fibre feeds - and both digital and analogue technology was in use. (Five used fibre in London and satellite elsewhere - and the Beeb use Astra 2D off-air in the Channel Islands...)

For digital I believe the transmitters are universfed with two digital distribution feeds via different routes to provide redundancy in a different manner. Fibre is universally used to feed the digital transmitters - and there is quite a lot more processing at the transmitter compared to analogue.

AIUI most broadcasters have multiple playout and multiple encoding and multiplexing operations to generate their digital services as well.

The BBC have two main playout areas in two locations, two main coding and mux operations in two locations (though not the same two). They have two main internal vision network routing centres (they no longer route vision circuits through intermediate regions as they used to - so feeds from Glasgow don't go via Manchester and/or Birmingham as they used to) as well.

These days redundancy is engineered in a different manner.

Simply rebroadcasting an off-air digital mux may actually be problematic - as different transmitters have different IDs in their streams, so you'd have to demux and remux on-site if you did that?

The Muxing of Mux 1 ( DTT) in Wales has a number of differences from those in the rest of the country (BBC2W, Radio Wales and Radio Cymru) and as such any duplication would be needed pretty damn close to BH in Cardiff. It'll be interested to see what explanation is offered for the power cut and the failure of a backup supply.

Yep - same is true in NI and Scotland I believe - with similar radio and BBC Two differences to the generic BBC Mux 1 English operation (where BBC One is CBR to allow a local version to be permanently dropped in to replace it)



Yep - these days either the generators aren't checked (either run up routinely or their fuel supplies monitored), the power switching isn't properly engineered or the important kit fed by them doesn't have a UPS to clean up the power and sustain during the change-over without a reboot required...

Analogue kit would flash and bang briefly when hit by a power glitch - digital stuff often crashes, reboots, or worse, corrupts its settings... (That is one reason Omnibus kit was so popular - it ran on the Acorn Risc OS platform rather than Windows - and rebooted in a couple of seconds...)

That's true, but surely a system of dropping in a "sustaining" (for want of a better word" feed of Mux1 from London in the event that wherever the Wales version is encoded is out of action is preferable to blank screens?

There are VBI idents carried to prevent RBS being invoked during opts, and I think these also form some protection against a transmitter RBL'ing an 'unauthorised' transmission, i.e. a foreign or wrong channel during lift conditions, or a local pirate 'hijack'.

When there used to be a pan-regional Westminster programme carried on BBC West, South, and South West, the normal Net1 feed from London to Southampton used to be routed via BBC Bristol from 5 mins before broadcast, until 5 mins after. This was then fed through BBC So'ton the usual way, and on to Rowridge. However Hannington and Midhurst did not recognise the Bristol VBI ident that suddenly appeared on Rowridge, and assumed they were being hijacked. They switched to RBS Crystal Palace. I'm told that this was only discovered because Bruce Parker the BBC South presenter, lived in Winchester, and was served by Hannington. He phoned up the studio in So'ton complaining he could not see the programme. (Obviously the only viewer ! )

Some opt-outs are also remotely controlled by VBI in the incoming video - where the opt switch is at the transmitter rather than the studio centre. If the incoming video is non-sync, or corrupted, the VBI detector loses the "Opt Out" data and reverts to the incoming sustaining feed. (This used to happen at BBC Cambridge - where mid-opt Norwich would appear for a few seconds - before Cambridge re-appeared again)

All analogue only...

ISTR that the regional analogue VBI IDs were carried in 4 bits of data - limiting them to 16 regions?

Norwich
Cambridge
Leeds
Hull
Southampton
Oxford
Birmingham
Nottingham
Pymouth
Jersey
Tunbridge Wells
London
Bristol
Manchester
Newcastle

Which leaves 15 English regions/sub-regions on BBC One and 18 BBC One variations in total, so I guess the nations are handled differently, IDs are being shared, or there is no longer a 4 bit limit?

Cardiff
Belfast
Glasgow

Awww. I have a picture in my head of a certain lady looking out of her front door to see if the building is still standing, then throwing her coat on as she dashes down the road into BH to see what's happened

So much for the best laid contingency plans

The Isle of Man feeds are switched between RBL Caldbeck usually but switching to Winter Hill so it can take North West regional opts. Presumably Caldbeck provides a better signal but a degraded signal is acceptable during opt outs.