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digital TV - what the blazes?

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Telly people - what is this all about? Our TV isn't connected to anything for transmitting signals, it can only receive them. Where is it searching? Will it ever download anything, and if so, how? (no upstream means no error-checking, no requests to re-start transfer or re-transmit that missed packet, etc.)

Seriously, what the hell?
2nd Sep 2008, 19:08  

It downloads the latest version of the software which is broadcast as part of the digital service. When it is downloaded it checks it against the SW in the box and if it is different it then tells you it is upgrading..

2nd Sep 2008, 20:02

tullis says:

It's done over the Engineering Channel, which is broadcast on the BBC multiplex.

This is to achieve the greatest coverage, for upgrading the largest amount of tellies possible.

2nd Sep 2008, 20:43

Salome says:

how funny.

2nd Sep 2008, 22:10

michaelpj says:

Digital TV is forward error corrected, which means that extra error-correction information is sent as part of the data stream. Your digital TV can use this extra information to recover the original data even in the presence of transmission errors. If the error rate become too high, this mechanism fails, leading to errors in the picture.

File-based data, like software upgrades, interactive applications and Digital Text are sent out on a carousel mechanism, where the files are transmitted one after another, over and over again. Checksums are used to ensure that a file is received correctly - if it's wholly or partially corrupt, the receiver waits for it to come around again on the carousel. Analogue teletext works the same way.

This mechanism is a bit cumbersome, but it avoids the need for a return path from your TV to the broadcasters.

3rd Sep 2008, 09:04

mat says:

Thanks, telly people. :D

Thelly people.

3rd Sep 2008, 13:01