Sky TV - the technology

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Andehh

Original Poster:

7,107 posts

205 months

Wednesday 17th December 2014
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Just noticed that one of my recorded programmes is 3gb, for an hour long episode. With sky TV getting me these programmes via the satellite are they really beaming me 3gb/hour based on my HD choice? So watching a few hours an evening very quickly adds up, throw in a few million other people makes that an insane amount of data, all from a few satellites.

What am I missing here? Codecs or encoding that reduces the "beamed" size?

Jonny_

4,108 posts

206 months

Wednesday 17th December 2014
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Not quite. Satellite telly is a broadcast rather than a 2-way data connection. Each channel is a specific frequency or band of frequencies, transmitted constantly and received by all users simultaneously. So although you've received 3gb of video, so has every other of the thousands/millions of people who watched it.

Edited by Jonny_ on Wednesday 17th December 20:53

Andehh

Original Poster:

7,107 posts

205 months

Wednesday 17th December 2014
quotequote all
Thanks, im intrigued now. So the hour long programme recorded was 3gb, so is that satellite broadcasting each channel (HD for example...) at a rate of 3ish gb an hour? Multiplied by 150(ish) channels?

Ynox

1,702 posts

178 months

Wednesday 17th December 2014
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Trying to put this in simple speak...spent a few years working in this industry and have a deep personal interest so it might be a little too technical though!

There's a few satellites at the orbital position(s) that Sky use. These are 28.2 degrees east and 28.5 degrees east.

Each satellite has multiple transponders, each of these (depending on bit rate of the stream - i.e. is it a 'premium' channel like Sky Movies / Sports / BBC1, or a crappy music channel) can broadcast multiple channels. This could be anything from 4 channels (if HD) to 15 channels (if crap bitrate SD).

At 28.2 there's around 40 or so transponders (http://www.lyngsat.com/Eutelsat-28A-and-Astra-2A-2E-2F.html), all of these are broadcasting all the time, to everyone. You just tune your box into the right frequency. Off the top of my head a transponder runs at about 40MBit/sec, so this would work out to around 18 gigabytes an hour (if I've not screwed up my maths). This means there's around 720 gigabytes / hour being broadcast by these satellites. But because you just tune to it, you only have to broadcast this - regardless how many subscribers you have.

As such, satellite is a very, very good way of broadcasting a lot of data to a lot of people at once (with the exception of latency and not taking into account the cost of launching the things!).

Ynox

1,702 posts

178 months

Wednesday 17th December 2014
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Andehh said:
Thanks, im intrigued now. So the hour long programme recorded was 3gb, so is that satellite broadcasting each channel (HD for example...) at a rate of 3ish gb an hour? Multiplied by 150(ish) channels?
Pretty much. My answer above covers this a bit more. Depends on the bit rate of the channel.

Andehh

Original Poster:

7,107 posts

205 months

Thursday 18th December 2014
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Many thanks Yonox, very interesting (I'm an engineer, so I'm sad like that!) & just the right level of detail! smile

Magic919

14,126 posts

200 months

Friday 19th December 2014
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How did you calculate the 3GB bit?

megaphone

10,694 posts

250 months

Friday 19th December 2014
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I give Sky satellite broadcasts a decade max, by that time everything will be streamed over the internet.

Ynox

1,702 posts

178 months

Friday 19th December 2014
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Still loads of places with crap net connections - satellite is still the winner really for broadcasting large amounts of video.

As for 3gb/hour - could guesstimate it based on capacity of hard disk on Sky box (i.e. 500gb) and percentage used by recording.

Andehh

Original Poster:

7,107 posts

205 months

Friday 19th December 2014
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Magic919 said:
How did you calculate the 3GB bit?
It came up in the menu when I was selecting stuff to watch, cant remember off the top of my head which one but I think It was in a folder of the series & when highlighting each episode it appeared below the image in top right hand corner? Something like that.

Magic919

14,126 posts

200 months

Friday 19th December 2014
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Ok. Sounds like some of the downloaded on demand content, rather than linear programmes.

AB

16,969 posts

194 months

Friday 19th December 2014
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Magic919 said:
Ok. Sounds like some of the downloaded on demand content, rather than linear programmes.
It's the space the recording takes up on the HDD... ?

Magic919

14,126 posts

200 months

Friday 19th December 2014
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AB said:
It's the space the recording takes up on the HDD... ?
Is that some kind of question?

AB

16,969 posts

194 months

Friday 19th December 2014
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Magic919 said:
AB said:
It's the space the recording takes up on the HDD... ?
Is that some kind of question?
I suppose the question is; what makes you think it is more likely downloaded on demand content, rather than linear programmes?

It's a programme taking up 3GB of space on his Sky HDD.

Magic919

14,126 posts

200 months

Friday 19th December 2014
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The fact that he was able to directly read the size of the asset amongst the programme metadata. My Sky box only does that for the on demand content. For linear recordings it gives a percentage, not size on disk.

pozi

1,723 posts

186 months

Saturday 20th December 2014
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megaphone said:
I give Sky satellite broadcasts a decade max, by that time everything will be streamed over the internet.
Unlikely, our existing archaic phone cabling simply won't be replaced quick enough to support the multicast technology needed to do IPTV properly.

I mean some homes are still struggling to even get decent ADSL connections frown